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Several genes involved in cytochrome P450, phase I, and glucuronosyltransferases conjugation catalysis in phase II are regulated by phenobarbital(PB) as well the transport mediated pathways of drug elimination. Induction of PB in xenobiotic-metabolizes of cytochromes CYP2b undergoes a transcriptional process, thus raising mRNA levels. Expression of the CAR summarized in a UniGene database, mainly in the kidney, liver, sometimes in the heart, GI tissues, and the human brain tissues. PB in the past ten years has been shown as an enhancer that is responsive to human(PBREM), rat(CYP2B), and the mouse; Constitutive Activated Receptor(CAR) identified was depicted to bind DR-4 motifs. The circulating thyroid hormone levels can be regulated by CAR. TH pathways of conjugation can be induced in PB treatment in a way that can lead to reductions that are fast-induced in T4 levels and serum triiodothyronine and finished serum thyroxine(T4).
Phase II and I enzymes PXR carries out induction. Expression of PXR is mainly evident in the liver, testis, human embryonic tissues, GI tract, and liver of the mouse. Research carried out on macrolide antibiotics, and glucocorticoids induction of CYP3A were perceived to utilize glucocorticoid receptor. This was explained by the induction of the CYP3A relationships obtained from the steroid structure-activity evaluation results. Research conducted in 1998 said that PXR was responsible for the induction of CYP3A and differences in the species in the induction of CYP3A by RIF and PCN. Based on this and other investigations, PXR has been perceived as a xenobiotic regulation mediator of CYP3A.
CAR has been depicted to be linked with a cofactor transcriptional induced by homeostasis energy regulation and fasting. Hemostasis of BA also aids in keeping the correct cholesterol levels. CAR can also impact gluconeogenesis regulation mediated by a transcription factor; the transcription factor binding can be regulated to Insulin Response Sequence(IRS). PXR protects the body from bile acid toxicity. Regarding the cholesterol levels regulation by CAR, PXR-null mice pretreatment using TCPOBOP does not reduce danger to cholesterol; therefore, toxicity from cholesterol can be controlled using PXR. | 1 | Biochemistry |
* Inoue Prize (2000)
* Chirality Medal (2005)
* Honorary member of the Italian National Academy of Sciences (2006)
* Science and Technology Prize from MEXT, the Japanese Ministry of Education, Culture, Sports, Science and Technology (2007)
* Chemical Society of Japan Award (2010)
* Japanese Purple Ribbon Medal (2012)
* Doctor Honoris Causa, University of Pannonia, Hungary, 2015 | 4 | Stereochemistry |
Lost-wax castingalso called investment casting, precision casting, or cire perdue (; borrowed from French)is the process by which a duplicate sculpture (often a metal, such as silver, gold, brass, or bronze) is cast from an original sculpture. Intricate works can be achieved by this method.
The oldest known examples of this technique are approximately 6,500-year-old (4550–4450 BC) and attributed to gold artefacts found at Bulgaria's Varna Necropolis. A copper amulet from Mehrgarh, Indus Valley civilization, in Pakistan, is dated to circa 4,000 BC. Cast copper objects, found in the Nahal Mishmar hoard in southern Israel, which belong to the Chalcolithic period (4500–3500 BC), are estimated, from carbon-14 dating, to date to circa 3500 BC. Other examples from somewhat later periods are from Mesopotamia in the third millennium BC. Lost-wax casting was widespread in Europe until the 18th century, when a piece-moulding process came to predominate.
The steps used in casting small bronze sculptures are fairly standardized, though the process today varies from foundry to foundry (in modern industrial use, the process is called investment casting). Variations of the process include: "lost mould", which recognizes that materials other than wax can be used (such as tallow, resin, tar, and textile); and "waste wax process" (or "waste mould casting"), because the mould is destroyed to remove the cast item. | 8 | Metallurgy |
In 2001, a cow named Bessie gave birth to a cloned Asian gaur, an endangered species, but the calf died after two days. In 2003, a banteng was successfully cloned, followed by three African wildcats from a thawed frozen embryo. These successes provided hope that similar techniques (using surrogate mothers of another species) might be used to clone extinct species. Anticipating this possibility, tissue samples from the last bucardo (Pyrenean ibex) were frozen in liquid nitrogen immediately after it died in 2000. Researchers are also considering cloning endangered species such as the Giant panda and Cheetah.
In 2002, geneticists at the Australian Museum announced that they had replicated DNA of the thylacine (Tasmanian tiger), at the time extinct for about 65 years, using polymerase chain reaction. However, on 15 February 2005 the museum announced that it was stopping the project after tests showed the specimens' DNA had been too badly degraded by the (ethanol) preservative. On 15 May 2005 it was announced that the thylacine project would be revived, with new participation from researchers in New South Wales and Victoria.
In 2003, for the first time, an extinct animal, the Pyrenean ibex mentioned above was cloned, at the Centre of Food Technology and Research of Aragon, using the preserved frozen cell nucleus of the skin samples from 2001 and domestic goat egg-cells. The ibex died shortly after birth due to physical defects in its lungs. | 1 | Biochemistry |
Chiral auxiliaries are generally reliable and versatile, enabling the synthesis of a large number of enantiomerically pure compounds in a time-efficient manner. Consequently, chiral auxiliaries are often the method of choice in the early phases of drug development. | 4 | Stereochemistry |
A compressor map is a chart which shows the performance of a turbomachinery compressor. This type of compressor is used in gas turbine engines, for supercharging reciprocating engines and for industrial processes, where it is known as a dynamic compressor. A map is created from compressor rig test results or predicted by a special computer program. Alternatively the map of a similar compressor can be suitably scaled. This article is an overview of compressor maps and their different applications and also has detailed explanations of maps for a fan and intermediate and high-pressure compressors from a three-shaft aero-engine as specific examples.
Compressor maps are an integral part of predicting the performance of gas turbine and turbocharged engines, both at design and off-design conditions. They also serve a critical purpose in selecting the correct compressors for industrial processes.
Fans and turbines also have operating maps, although the latter are significantly different in appearance to that of compressors. | 7 | Physical Chemistry |
(AD 450(?)–1500)
Utilitarian and ceremonial objects; objects of personal adornment
#Chipal, Guatemala
#Chutixtiox, Guatemala
#Copán, Honduras
#Kaminaljuyú, Guatemala
#Motagua River valley, Guatemala
#Los Naranjos, Honduras
#Nebaj, Guatemala
#Quemistlá "Bell Caves", Honduras
#Quiriguá, Guatemala
#San Augustín Acasaguastlán, Guatemala
#Tajumulco, Guatemala
#Tazumal, El Salvador
#Zacualpa, Guatemala
#Zaculeu, Guatemala | 8 | Metallurgy |
In atomic physics, a ridged mirror (or ridged atomic mirror, or Fresnel diffraction mirror) is a kind of atomic mirror, designed for the specular reflection of neutral particles (atoms) coming at a grazing incidence angle. In order to reduce the mean attraction of particles to the surface and increase the reflectivity, this surface has narrow ridges. | 7 | Physical Chemistry |
Microarray-based methods are a logical extension of the technologies available to analyze bisulfite-treated DNA to allow for genome-wide analysis of methylation. Oligonucleotide microarrays are designed using pairs of oligonucleotide hybridization probes targeting CpG sites of interest. One is complementary to the unaltered methylated sequence, and the other is complementary to the C-to-U-converted unmethylated sequence. The probes are also bisulfite-specific to prevent binding to DNA incompletely converted by bisulfite. The Illumina Methylation Assay is one such assay that applies the bisulfite sequencing technology on a microarray level to generate genome-wide methylation data. | 1 | Biochemistry |
The nitrogen-vacancy center is a point defect in the diamond lattice. It consists of a nearest-neighbor pair of a nitrogen atom, which substitutes for a carbon atom, and a lattice vacancy.
Two charge states of this defect, neutral NV and negative NV, are known from spectroscopic studies using optical absorption, photoluminescence (PL), electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR), which can be viewed as a hybrid of PL and EPR; most details of the structure originate from EPR. The nitrogen atom on one hand has five valence electrons. Three of them are covalently bonded to the carbon atoms, while the other two remain non-bonded and are called a lone pair. The vacancy on the other hand has three unpaired electrons. Two of them form a quasi covalent bond and one remains unpaired. The overall symmetry, however, is axial (trigonal C); one can visualize this by imagining the three unpaired vacancy electrons continuously exchanging their roles.
The NV thus has one unpaired electron and is paramagnetic. However, despite extensive efforts, electron paramagnetic resonance signals from NV avoided detection for decades until 2008. Optical excitation is required to bring the NV defect into the EPR-detectable excited state; the signals from the ground state are presumably too broad for EPR detection.
The NV centers can be converted into NV by changing the Fermi level position. This can be achieved by applying external voltage to a p-n junction made from doped diamond, e.g., in a Schottky diode.
In the negative charge state NV, an extra electron is located at the vacancy site forming a spin S=1 pair with one of the vacancy electrons. As in NV, the vacancy electrons are "exchanging roles" preserving the overall trigonal symmetry. This NV state is what is commonly, and somewhat incorrectly, called "the nitrogen-vacancy center". The neutral state is not generally used for quantum technology.
The NV centers are randomly oriented within a diamond crystal. Ion implantation techniques can enable their artificial creation in predetermined positions. | 7 | Physical Chemistry |
Conventionally, they are displayed as isosurfaces with positive density—electron density where theres nothing in the model, usually corresponding to some constituent of the crystal that hasnt been modelled, for example a ligand or a crystallisation adjutant -- in green, and negative density—parts of the model not backed up by electron density, indicating either that an atom has been disordered by radiation damage or that it is modelled in the wrong place—in red. The typical contouring (display threshold) is set at 3σ. | 3 | Analytical Chemistry |
* 1802 – Joseph Louis Gay-Lussac publishes Charless law, discovered (but unpublished) by Jacques Charles around 1787; this shows the dependency between temperature and volume. Gay-Lussac also formulates the law relating temperature with pressure (the pressure law, or Gay-Lussacs law)
* 1804 – Sir John Leslie observes that a matte black surface radiates heat more effectively than a polished surface, suggesting the importance of black-body radiation
* 1805 – William Hyde Wollaston defends the conservation of energy in On the Force of Percussion
* 1808 – John Dalton defends caloric theory in A New System of Chemistry and describes how it combines with matter, especially gases; he proposes that the heat capacity of gases varies inversely with atomic weight
* 1810 – Sir John Leslie freezes water to ice artificially
* 1813 – Peter Ewart supports the idea of the conservation of energy in his paper On the measure of moving force; the paper strongly influences Dalton and his pupil, James Joule
* 1819 – Pierre Louis Dulong and Alexis Thérèse Petit give the Dulong-Petit law for the specific heat capacity of a crystal
* 1820 – John Herapath develops some ideas in the kinetic theory of gases but mistakenly associates temperature with molecular momentum rather than kinetic energy; his work receives little attention other than from Joule
* 1822 – Joseph Fourier formally introduces the use of dimensions for physical quantities in his Théorie Analytique de la Chaleur
* 1822 – Marc Seguin writes to John Herschel supporting the conservation of energy and kinetic theory
* 1824 – Sadi Carnot analyzes the efficiency of steam engines using caloric theory; he develops the notion of a reversible process and, in postulating that no such thing exists in nature, lays the foundation for the second law of thermodynamics, and initiating the science of thermodynamics
* 1827 – Robert Brown discovers the Brownian motion of pollen and dye particles in water
* 1831 – Macedonio Melloni demonstrates that black-body radiation can be reflected, refracted, and polarised in the same way as light
* 1834 – Émile Clapeyron popularises Carnots work through a graphical and analytic formulation. He also combined Boyles Law, Charless Law, and Gay-Lussacs Law to produce a Combined Gas Law. PV/T = k
* 1841 – Julius Robert von Mayer, an amateur scientist, writes a paper on the conservation of energy, but his lack of academic training leads to its rejection
* 1842 – Mayer makes a connection between work, heat, and the human metabolism based on his observations of blood made while a ship's surgeon; he calculates the mechanical equivalent of heat
* 1842 – William Robert Grove demonstrates the thermal dissociation of molecules into their constituent atoms, by showing that steam can be disassociated into oxygen and hydrogen, and the process reversed
* 1843 – John James Waterston fully expounds the kinetic theory of gases, but according to D Levermore "there is no evidence that any physical scientist read the book; perhaps it was overlooked because of its misleading title, Thoughts on the Mental Functions."
* 1843 – James Joule experimentally finds the mechanical equivalent of heat
* 1845 – Henri Victor Regnault added Avogadro's Law to the Combined Gas Law to produce the Ideal Gas Law. PV = nRT
* 1846 – Grove publishes an account of the general theory of the conservation of energy in On The Correlation of Physical Forces
* 1847 – Hermann von Helmholtz publishes a definitive statement of the conservation of energy, the first law of thermodynamics | 7 | Physical Chemistry |
Current optical data storage media, such as the CD and DVD store data as a series of reflective marks on an internal surface of a disc. In order to increase storage capacity, it is possible for discs to hold two or even more of these data layers, but their number is severely limited since the addressing laser interacts with every layer that it passes through on the way to and from the addressed layer. These interactions cause noise that limits the technology to approximately 10layers. 3D optical data storage methods circumvent this issue by using addressing methods where only the specifically addressed voxel (volumetric pixel) interacts substantially with the addressing light. This necessarily involves nonlinear data reading and writing methods, in particular nonlinear optics.
3D optical data storage is related to (and competes with) holographic data storage. Traditional examples of holographic storage do not address in the third dimension, and are therefore not strictly "3D", but more recently 3D holographic storage has been realized by the use of microholograms. Layer-selection multilayer technology (where a multilayer disc has layers that can be individually activated e.g. electrically) is also closely related.
As an example, a prototypical 3D optical data storage system may use a disc that looks much like a transparent DVD. The disc contains many layers of information, each at a different depth in the media and each consisting of a DVD-like spiral track. In order to record information on the disc a laser is brought to a focus at a particular depth in the media that corresponds to a particular information layer. When the laser is turned on it causes a photochemical change in the media. As the disc spins and the read/write head moves along a radius, the layer is written just as a DVD-R is written. The depth of the focus may then be changed and another entirely different layer of information written. The distance between layers may be 5 to 100 micrometers, allowing >100 layers of information to be stored on a single disc.
In order to read the data back (in this example), a similar procedure is used except this time instead of causing a photochemical change in the media the laser causes fluorescence. This is achieved e.g. by using a lower laser power or a different laser wavelength. The intensity or wavelength of the fluorescence is different depending on whether the media has been written at that point, and so by measuring the emitted light the data is read.
The size of individual chromophore molecules or photoactive color centers is much smaller than the size of the laser focus (which is determined by the diffraction limit). The light, therefore, addresses a large number (possibly even 10) of molecules at any one time, so the medium acts as a homogeneous mass rather than a matrix structured by the positions of chromophores. | 5 | Photochemistry |
FSL constructs, when in solution (saline) and in contact, will spontaneously incorporate into cell membranes. The methodology involves simply preparing a solution of FSL constructs in the range of 1–1000 μg/mL, with the concentration used determining the amount of antigen present on the kodecyte. The ability to control antigen levels on the outside of a kodecyte has allowed for manufacture of quality control sensitivity systems and serologic teaching kits incorporating the entire range of serologic agglutination reactions. The actual concentration will depend on the construct and the quantity of construct required in the membrane. One part of FSL solution is added to one part of cells (up to 100% suspension) and they are incubated at a set temperature within the range of 4–37 °C (39–99 °F) depending on temperature compatibility of the cells being modified. The higher the temperature, the faster the rate of FSL insertion into the membrane. For red blood cells incubation for 2 hours at 37 °C achieves >95% FSL insertion with at least 50% insertion being achieved within 20 minutes. In general, for carbohydrate based FSLs insertion into red blood cells, incubation for 4 hours at room temperature or 20 hours at 4 °C are similar to one hour at 37 °C . The resultant kodecytes do not required to be washed, however this option should be considered if an excess of FSL construct is used in the "koding process".
Kodecytes can also be created in vivo by injection of constructs directly into the circulation. However this process will modify all cells in contact with the constructs and usually require significantly more construct than in vitro preparation, as FSL constructs will preferentially associate with free lipids.
The in vivo creation of kodecytes is untargeted and FSL constructs will insert into all cells non-specifically, but may show a preference for some cell types.
Diagnostic serological analyses including flow cytometry and scanning electron microscopy usually can't see a difference between "kodecytes" and unmodified cells. However, when compared with natural cells there does appear to be a difference between IgM and IgG antibody reactivities when the functional group (F) is a monomeric peptide antigen. IgM antibodies appear to react poorly with kodecytes made with FSL peptides. Furthermore, FSL constructs may have a restricted antigen/epitope and may not react with a monoclonal antibody unless the FSL construct and monoclonal antibody are complementary.
Kodecytes can be studied using standard histological techniques. Kodecytes can be fixed after "koding" subject to the functional moiety (F) of the FSL construct being compatible with the fixative. However, freeze cut or formalin-fixed freeze cut tissues are required because the lipid based FSL constructs (and other glycolipids) will be leached from the "kodecytes" in paraffin imbedded samples during the deparaffination steps. | 1 | Biochemistry |
MS-SnuPE employs the primer extension method initially designed for analyzing single-nucleotide polymorphisms. DNA is bisulfite-converted, and bisulfite-specific primers are annealed to the sequence up to the base pair immediately before the CpG of interest. The primer is allowed to extend one base pair into the C (or T) using DNA polymerase terminating dideoxynucleotides, and the ratio of C to T is determined quantitatively.
A number of methods can be used to determine this C:T ratio. At the beginning, MS-SnuPE relied on radioactive ddNTPs as the reporter of the primer extension. Fluorescence-based methods or Pyrosequencing can also be used. However, matrix-assisted laser desorption ionization/time-of-flight (MALDI-TOF) mass spectrometry analysis to differentiate between the two polymorphic primer extension products can be used, in essence, based on the GOOD assay designed for SNP genotyping. Ion pair reverse-phase high-performance liquid chromatography (IP-RP-HPLC) has also been used to distinguish primer extension products. | 1 | Biochemistry |
These compounds form during the catabolism of carbohydrates and lipids in condensation reactions, and in some other metabolic reactions of the amino acids. Oxygen is produced by plants and some bacteria in photosynthesis, while CO is a waste product of all animals and plants. Nitrogen gases are produced by denitrifying bacteria and as a waste product, and bacteria for decaying yield ammonia, as do most invertebrates and vertebrates. Water is the only liquid waste from animals and photosynthesizing plants. | 1 | Biochemistry |
α-Keggin anions have been used as catalyst in the following reactions: hydration, polymerization and oxidation reaction as catalysts. Japanese chemical companies have commercialized the use of the compounds in hydration of propene, oxidation of methacrolein, hydration of isobutene and n-butene, and polymerization of THF. | 7 | Physical Chemistry |
Another class of plant disease resistance genes opens a “trap door” that quickly kills invaded cells, stopping pathogen proliferation. Xanthomonas and Ralstonia transcription activator–like (TAL) effectors are DNA-binding proteins that activate host gene expression to enhance pathogen virulence. Both the rice and pepper lineages independently evolved TAL-effector binding sites that instead act as an executioner that induces hypersensitive host cell death when up-regulated. Xa27 from rice and Bs3 and Bs4c from pepper, are such “executor” (or "executioner") genes that encode non-homologous plant proteins of unknown function. Executor genes are expressed only in the presence of a specific TAL effector.
Engineered executor genes were demonstrated by successfully redesigning the pepper Bs3 promoter to contain two additional binding sites for TAL effectors from disparate pathogen strains. Subsequently, an engineered executor gene was deployed in rice by adding five TAL effector binding sites to the Xa27 promoter. The synthetic Xa27 construct conferred resistance against Xanthomonas bacterial blight and bacterial leaf streak species. | 1 | Biochemistry |
Calcium carbide reacts with nitrogen at high temperature to form calcium cyanamide:
:CaC + N → CaCN + C
Commonly known as nitrolime, calcium cyanamide is used as fertilizer. It is hydrolysed to cyanamide, HNCN. | 8 | Metallurgy |
This form of photophosphorylation occurs on the stroma lamella, or fret channels. In cyclic photophosphorylation, the high-energy electron released from P700, a pigment in a complex called photosystem I, flows in a cyclic pathway. The electron starts in photosystem I, passes from the primary electron acceptor to ferredoxin and then to plastoquinone, next to cytochrome bf (a similar complex to that found in mitochondria), and finally to plastocyanin before returning to photosystem I. This transport chain produces a proton-motive force, pumping H ions across the membrane and producing a concentration gradient that can be used to power ATP synthase during chemiosmosis. This pathway is known as cyclic photophosphorylation, and it produces neither O nor NADPH. Unlike non-cyclic photophosphorylation, NADP does not accept the electrons; they are instead sent back to the cytochrome bf complex.
In bacterial photosynthesis, a single photosystem is used, and therefore is involved in cyclic photophosphorylation.
It is favored in anaerobic conditions and conditions of high irradiance and CO compensation points. | 5 | Photochemistry |
Microarray image processing must correctly identify the regular grid of features within an image and independently quantify the fluorescence intensity for each feature. Image artefacts must be additionally identified and removed from the overall analysis. Fluorescence intensities directly indicate the abundance of each sequence, since the sequence of each probe on the array is already known.
The first steps of RNA-seq also include similar image processing; however, conversion of images to sequence data is typically handled automatically by the instrument software. The Illumina sequencing-by-synthesis method results in an array of clusters distributed over the surface of a flow cell. The flow cell is imaged up to four times during each sequencing cycle, with tens to hundreds of cycles in total. Flow cell clusters are analogous to microarray spots and must be correctly identified during the early stages of the sequencing process. In Roche’s pyrosequencing method, the intensity of emitted light determines the number of consecutive nucleotides in a homopolymer repeat. There are many variants on these methods, each with a different error profile for the resulting data. | 1 | Biochemistry |
Paired box protein Pax-6 in humans is a transcription factor, which is a main regulatory gene of eye and brain development. Ectopic expression of Drosophila homolog eyeless (ey) has been used to identify roles of Pax-6 in humans. Using tissue specific UAS-Gal4 system, ey can be induced on the legs, wings, halters and antennae of the transgenic flies to demonstrate that functions of ey. | 1 | Biochemistry |
Trichloroacetonitrile is an organic compound with the formula CClCN. It is a colourless liquid, although commercial samples often are brownish. It is used commercially as a precursor to the fungicide etridiazole. It is prepared by dehydration of trichloroacetamide. As a bifunctional compound, trichloroacetonitrile can react at both the trichloromethyl and the nitrile group. The electron-withdrawing effect of the trichloromethyl group activates the nitrile group for nucleophilic additions. The high reactivity makes trichloroacetonitrile a versatile reagent, but also causes its susceptibility towards hydrolysis. | 0 | Organic Chemistry |
Amoxicillin is relatively inexpensive. In 2022, a survey of eight generic antibiotics commonly prescribed in the United States found their average cost to be about $42.67, while amoxicillin was sold for $12.14 on average. | 4 | Stereochemistry |
Dry nylon-6 has a glass transition temperature of . Nylon-6,6 in the dry state has a glass transition temperature of about . Whereas polyethene has a glass transition range of
The above are only mean values, as the glass transition temperature depends on the cooling rate and molecular weight distribution and could be influenced by additives. For a semi-crystalline material, such as polyethene that is 60–80% crystalline at room temperature, the quoted glass transition refers to what happens to the amorphous part of the material upon cooling. | 7 | Physical Chemistry |
Electroporation allows cellular introduction of large highly charged molecules such as DNA which would never passively diffuse across the hydrophobic bilayer core. This phenomenon indicates that the mechanism is the creation of nm-scale water-filled holes in the membrane. Electropores were optically imaged in lipid bilayer models like droplet interface bilayers and giant unilamellar vesicles, while addition of cytoskeletal proteins such as actin networks to the giant unilamellar vesicles seem to prevent the formation of visible electropores. Experimental evidences for actin networks in regulating the cell membrane permeability has also emerged. Although electroporation and dielectric breakdown both result from application of an electric field, the mechanisms involved are fundamentally different. In dielectric breakdown the barrier material is ionized, creating a conductive pathway. The material alteration is thus chemical in nature. In contrast, during electroporation the lipid molecules are not chemically altered but simply shift position, opening up a pore which acts as the conductive pathway through the bilayer as it is filled with water.
Electroporation is a dynamic phenomenon that depends on the local transmembrane voltage at each point on the cell membrane. It is generally accepted that for a given pulse duration and shape, a specific transmembrane voltage threshold exists for the manifestation of the electroporation phenomenon (from 0.5 V to 1 V). This leads to the definition of an electric field magnitude threshold for electroporation (E). That is, only the cells within areas where E≧E are electroporated. If a second threshold (E) is reached or surpassed, electroporation will compromise the viability of the cells, i.e., irreversible electroporation (IRE).
Electroporation is a multi-step process with several distinct phases. First, a short electrical pulse must be applied. Typical parameters would be 300–400 mV for < 1 ms across the membrane (note- the voltages used in cell experiments are typically much larger because they are being applied across large distances to the bulk solution so the resulting field across the actual membrane is only a small fraction of the applied bias). Upon application of this potential the membrane charges like a capacitor through the migration of ions from the surrounding solution. Once the critical field is achieved there is a rapid localized rearrangement in lipid morphology. The resulting structure is believed to be a "pre-pore" since it is not electrically conductive but leads rapidly to the creation of a conductive pore. Evidence for the existence of such pre-pores comes mostly from the "flickering" of pores, which suggests a transition between conductive and insulating states. It has been suggested that these pre-pores are small (~3 Å) hydrophobic defects. If this theory is correct, then the transition to a conductive state could be explained by a rearrangement at the pore edge, in which the lipid heads fold over to create a hydrophilic interface. Finally, these conductive pores can either heal, resealing the bilayer or expand, eventually rupturing it. The resultant fate depends on whether the critical defect size was exceeded which in turn depends on the applied field, local mechanical stress and bilayer edge energy. | 1 | Biochemistry |
Photochromism was discovered in the late 1880s, including work by Markwald, who studied the reversible change of color of 2,3,4,4-tetrachloronaphthalen-1(4H)-one in the solid state. He labeled this phenomenon "phototropy", and this name was used until the 1950s when Yehuda Hirshberg, of the Weizmann Institute of Science in Israel proposed the term "photochromism". Photochromism can take place in both organic and inorganic compounds, and also has its place in biological systems (for example retinal in the vision process). | 5 | Photochemistry |
Hydrogel fiber can be produced by electrospinning with solidification done by the evaporation of the solvent. The fibrous state is created by the combination of electrostatic repulsion and the surface tension of the solution. But subsequent crosslinking is usually needed to form a crosslinked network. One advantage of electrospun hydrogel fiber is that it has a diameter in range in the order between nm to μm, which is desirable for fast matter exchange. However, utilization of single fiber can be hard to achieve due to the weak mechanical strength of the microscopic fiber and its entanglements after production.
An example of this method would be the production of polyacrylamide (PAAM) semi-interpretation network developed by Tahchi et al. Where the first linear PAAM (provide solidification) was mixed with AAM monomer (form subsequent network) and crosslinker N,N′-methylenebisacrylamide (MBA). During the electrospinning process, the linear PAAM provided the required physical properties to achieve electrospinning, while the AAM monomer and MBA crosslinker were used to form a second crosslinked network inside the PAAM fiber. Although no crosslinking was formed between the first and second networks, the physical entanglement will prevent linear PAAM from leaking. | 7 | Physical Chemistry |
Quorum sensing can be a useful tool for improving the function of self-organizing networks such as the SECOAS (Self-Organizing Collegiate Sensor) environmental monitoring system. In this system, individual nodes sense that there is a population of other nodes with similar data to report. The population then nominates just one node to report the data, resulting in power savings. Ad hoc wireless networks can also benefit from quorum sensing, by allowing the system to detect and respond to network conditions.
Quorum sensing can also be used to coordinate the behavior of autonomous robot swarms. Using a process similar to that used by Temnothorax ants, robots can make rapid group decisions without the direction of a controller. | 1 | Biochemistry |
Quality scores are normally stored together with the nucleotide sequence in the widely accepted FASTQ format. They account for about half of the required disk space in the FASTQ format (before compression), and therefore the compression of the quality values can significantly reduce storage requirements and speed up analysis and transmission of sequencing data. Both lossless and lossy compression are recently being considered in the literature. For example, the algorithm QualComp performs lossy compression with a rate (number of bits per quality value) specified by the user. Based on rate-distortion theory results, it allocates the number of bits so as to minimize the MSE (mean squared error) between the original (uncompressed) and the reconstructed (after compression) quality values. Other algorithms for compression of quality values include SCALCE, Fastqz and more recently QVZ, AQUa and the MPEG-G standard, that is currently under development by the MPEG standardisation working group. Both are lossless compression algorithms that provide an optional controlled lossy transformation approach. For example, SCALCE reduces the alphabet size based on the observation that “neighboring” quality values are similar in general. | 1 | Biochemistry |
The electronic transitions of molecules in solution can depend strongly on the type of solvent with additional bathochromic shifts or hypsochromic shifts. | 7 | Physical Chemistry |
The murexide test is an analytical technique to identify the presence of caffeine and other purine derivatives in a sample. These compounds do not respond to the common alkaloid identification tests such as Dragendorff's reagent. In this test, crude drugs (to be identified) are mixed with a tiny amount of potassium chlorate and a drop of hydrochloric acid. The sample is then evaporated to dryness and the resulting residue is exposed to ammonia vapour. Purine alkaloids produce a pinkish-purple color in this test due to formation of murexide (ammonium purpurate; appears purple in pure state), which the test is named after.
In pure form, murexide appears purple, but when it is produced by reaction of acidified solutions of purines and ammonia, various shades of purple and pink are produced. | 3 | Analytical Chemistry |
N-Iodosuccinimide (NIS) is a reagent used in organic chemistry for the iodination of alkenes and as a mild oxidant.
NIS is the iodine analog of N-chlorosuccinimide (NCS) and N-bromosuccinimide (NBS) which are used for similar applications. | 0 | Organic Chemistry |
The transcription, a complete set of general transcription factors and RNA polymerase need to be assembled at the core promoter to form the ~2.5 million Dalton preinitiation complex. For example, for promoters that contain a TATA box near the TSS, the recognition of TATA box by the TBP subunit of TFIID initiates the assembly of a transcription complex. The next proteins to enter are TFIIA and TFIIB, which stabilize the DNA-TFIID complex and recruit Pol II in association with TFIIF and additional transcription factors. TFIIB serves as the bridge between the TATA-bound TBP and the RNA polymerase. It also helps to place the active centre of the polymerase in the correct position to initiate transcription. One of the last transcription factors to be recruited to the preinitiation complex is TFIIH, which plays an important role in promoter melting and escape. | 1 | Biochemistry |
In polymer chemistry, a random coil is a conformation of polymers where the monomer subunits are oriented randomly while still being bonded to adjacent units. It is not one specific shape, but a statistical distribution of shapes for all the chains in a population of macromolecules. The conformation's name is derived from the idea that, in the absence of specific, stabilizing interactions, a polymer backbone will "sample" all possible conformations randomly. Many unbranched, linear homopolymers — in solution, or above their melting temperatures — assume (approximate) random coils. | 7 | Physical Chemistry |
Most antibodies have the similar structure except the hypervariable region which is called the antigen binding site. This region is constituted by the combination of various amino acids. When the antigen is a kind of carbohydrate (Polysaccharide), the binding could be regarded as a protein-carbohydrate interaction. | 0 | Organic Chemistry |
Since thienamycin decomposes in the presence of water, it is impractical for the clinical treatment of bacterial infections, so stable derivatives were created for medicinal consumption. One such derivative, imipenem, was formulated in 1985. Imipenem, an N-formimidoyl derivative of thienamycin, is rapidly metabolized by a renal dipeptidase enzyme found in the human body. To prevent its rapid degradation, imipenem is normally coadministered with cilastatin, an inhibitor of this enzyme. | 0 | Organic Chemistry |
In humans, ERVs have been proposed to be involved in multiple sclerosis (MS). A specific association between MS and the ERVWE1, or "syncytin", gene, which is derived from an ERV insertion, has been reported, along with the presence of an "MS-associated retrovirus" (MSRV), in patients with the disease. Human ERVs (HERVs) have also been implicated in ALS and addiction.
In 2004 it was reported that antibodies to HERVs were found in greater frequency in the sera of people with schizophrenia. Additionally, the cerebrospinal fluid of people with recent onset schizophrenia contained levels of a retroviral marker, reverse transcriptase, four times higher than control subjects. Researchers continue to look at a possible link between HERVs and schizophrenia, with the additional possibility of a triggering infection inducing schizophrenia. | 1 | Biochemistry |
About 70% of a humans total energy expenditure is due to the basal life processes taking place in the organs of the body (see table). About 20% of ones energy expenditure comes from physical activity and another 10% from thermogenesis, or digestion of food (postprandial thermogenesis). All of these processes require an intake of oxygen along with coenzymes to provide energy for survival (usually from macronutrients like carbohydrates, fats, and proteins) and expel carbon dioxide, due to processing by the Krebs cycle.
For the BMR, most of the energy is consumed in maintaining fluid levels in tissues through osmoregulation, and only about one-tenth is consumed for mechanical work, such as digestion, heartbeat, and breathing.
What enables the Krebs cycle to perform metabolic changes to fats, carbohydrates, and proteins is energy, which can be defined as the ability or capacity to do work. The breakdown of large molecules into smaller molecules—associated with release of energy—is catabolism. The building up process is termed anabolism. The breakdown of proteins into amino acids is an example of catabolism, while the formation of proteins from amino acids is an anabolic process.
Exergonic reactions are energy-releasing reactions and are generally catabolic. Endergonic reactions require energy and include anabolic reactions and the contraction of muscle. Metabolism is the total of all catabolic, exergonic, anabolic, endergonic reactions.
Adenosine triphosphate (ATP) is the intermediate molecule that drives the exergonic transfer of energy to switch to endergonic anabolic reactions used in muscle contraction. This is what causes muscles to work which can require a breakdown, and also to build in the rest period, which occurs during the strengthening phase associated with muscular contraction. ATP is composed of adenine, a nitrogen containing base, ribose, a five carbon sugar (collectively called adenosine), and three phosphate groups. ATP is a high energy molecule because it stores large amounts of energy in the chemical bonds of the two terminal phosphate groups. The breaking of these chemical bonds in the Krebs Cycle provides the energy needed for muscular contraction. | 1 | Biochemistry |
For MLL, two isomers are possible - a facial isomer (fac) in which each set of three identical ligands occupies one face of the octahedron surrounding the metal atom, so that any two of these three ligands are mutually cis, and a meridional isomer (mer) in which each set of three identical ligands occupies a plane passing through the metal atom. | 4 | Stereochemistry |
Salt metathesis reaction of salts such as KCo(CO) with [Ru(CO)Cl] leads selectively to mixed-metal carbonyls such as RuCo(CO).
:4 KCo(CO) + [Ru(CO)Cl] → 2 RuCo(CO) + 4 KCl + 11 CO | 0 | Organic Chemistry |
The Maximum entropy method is an analysis method that has great developmental potential. The method is also used for the quantification of sedimentation velocity data from analytical ultracentrifugation. The maximum entropy method involves several iterative steps to minimize the deviation of the fitted data from the experimental data and subsequently reduce the χ of the fitted data. | 7 | Physical Chemistry |
The first known use of silver was in the Near East in Anatolia and Mesopotamia during the 4th and 3rd millennium BC, the Early Bronze Age. Archaeological findings of silver and lead objects together with litharge pieces and slag have been studied in a variety of sites. Although this has been interpreted as silver being extracted from lead ores, it has been also suggested that lead was added to collect silver from visible silver minerals embedded in host rock. In both cases silver would be retrieved from lead metal by cupellation.
During the following Iron Age, cupellation was done by fusing the base metals with a surplus of lead. The bullion or product of this fusion was then heated in a cupellation furnace to separate the noble metals. Mines such as Rio Tinto, near Huelva in Spain, became an important political and economic site around the Mediterranean Sea, as well as Laurion in Greece. Around 500 BC control over the Laurion mines gave Athens political advantage and power in the Mediterranean so that they were able to defeat the Persians.
During the Roman times, the empire needed large quantities of lead to support the Roman civilization over a great territory; they searched for open lead-silver mines in areas they conquered. Silver coinage became the normalised medium of exchange, hence silver production and mine control gave economic and political power. In Roman times it was worth mining lead ores if their content of silver was 0.01% or more.
The origin of the use of cupellation for analysis is not known. One of the earliest written references to cupels is Theophilus Divers Ars in the 12th century AD. The process changed little until the 16th century.
Small-scale cupellation may be considered the most important fire assay developed in history, and perhaps the origin of chemical analysis. Most of the written evidence comes from the Renaissance in the 16th century. Vannoccio Biringuccio, Georg Agricola and Lazarus Ercker, among others, wrote about the art of mining and testing the ores, as well as detailed descriptions of cupellation. Their descriptions and assumptions have been identified in diverse archaeological findings through Medieval and Renaissance Europe. By these times the amount of fire assays increased considerably, mainly because of testing ores in the mines to identify the availability of its exploitation. A primary use of cupellation was related to minting activities, and it was also used in testing jewelry. Since the Renaissance, cupellation became a standardised method of analysis that has changed little, demonstrating its efficiency. Its development touched the spheres of economy, politics, warfare and power in ancient times. | 8 | Metallurgy |
A microbial desalination cell (MDC) is a biological electrochemical system that implements the use of electro-active bacteria to power desalination of water in situ, resourcing the natural anode and cathode gradient of the electro-active bacteria and thus creating an internal supercapacitor. Available water supply has become a worldwide endemic as only .3% of the Earth's water supply is usable for human consumption, while over 99% is sequestered by oceans, glaciers, brackish waters, and biomass. Current applications in electrocoagulation, such as microbial desalination cells, are able to desalinate and sterilize formerly unavailable water to render it suitable for safe water supply. Microbial desalination cells stem from microbial fuel cells, deviating by no longer requiring the use of a mediator and instead relying on the charged components of the internal sludge to power the desalination process. Microbial desalination cells therefore do not require additional bacteria to mediate the catabolism of the substrate during biofilm oxidation on the anodic side of the capacitor. MDCs and other bio-electrical systems are favored over reverse osmosis, nanofiltration and other desalination systems due to lower costs, energy and environmental impacts associated with bio-electrical systems. | 7 | Physical Chemistry |
Electrocatalysis for CO reduction is not practiced commercially but remains a topic of research. The reduction of CO into useable products is a potential way to combat climate change. Electrocatalysts can promote the reduction of carbon dioxide into methanol and other useful fuel and stock chemicals. The most valuable reduction products of CO are those that have a higher energy content, meaning that they can be reused as fuels. Thus, catalyst development focuses on the production of products such as methane and methanol. Homogeneous catalysts, such as enzymes and synthetic coordination complexes have been employed for this purpose. A variety of nanomaterials have also been studied for CO reduction, including carbon-based materials and framework materials. | 7 | Physical Chemistry |
F number is a correlation number used in the analysis of polycyclic aromatic hydrocarbons (PAHs) as a descriptor of their hydrophobicity and molecular size. It was proposed by Robert Hurtubise and co-workers in 1977. | 3 | Analytical Chemistry |
A core set of energy-producing catabolic pathways occur within all living organisms in some form. These pathways transfer the energy released by breakdown of nutrients into ATP and other small molecules used for energy (e.g. GTP, NADPH, FADH). All cells can perform anaerobic respiration by glycolysis. Additionally, most organisms can perform more efficient aerobic respiration through the citric acid cycle and oxidative phosphorylation. Additionally plants, algae and cyanobacteria are able to use sunlight to anabolically synthesize compounds from non-living matter by photosynthesis. | 1 | Biochemistry |
The PI3K/AKT pathway has a natural inhibitor called Phosphatase and tensin homolog (PTEN) whose function is to limit proliferation in cells, helping to prevent cancer. Knocking out PTEN has been shown to increase the mass of the brain because of the unregulated proliferation that occurs.
PTEN works by dephosphorylating PIP3 to PIP2 which limits AKTs ability to bind to the membrane, decreasing its activity. PTEN deficiencies can be compensated downstream to rescue differentiation or quiescence. Knocking out PTEN is not as serious as knocking out FOXO for this reason. | 1 | Biochemistry |
The retinoblastoma protein (protein name abbreviated Rb; gene name abbreviated Rb, RB or RB1) is a tumor suppressor protein that is dysfunctional in several major cancers. One function of pRb is to prevent excessive cell growth by inhibiting cell cycle progression until a cell is ready to divide. When the cell is ready to divide, pRb is phosphorylated, inactivating it, and the cell cycle is allowed to progress. It is also a recruiter of several chromatin remodeling enzymes such as methylases and acetylases.
pRb belongs to the pocket protein family, whose members have a pocket for the functional binding of other proteins. Should an oncogenic protein, such as those produced by cells infected by high-risk types of human papillomavirus, bind and inactivate pRb, this can lead to cancer. The RB gene may have been responsible for the evolution of multicellularity in several lineages of life including animals. | 1 | Biochemistry |
Certified reference materials (CRMs) are controls or standards used to check the quality and metrological traceability of products, to validate analytical measurement methods, or for the calibration of instruments. A certified reference material is a particular form of measurement standard.
Reference materials are particularly important for analytical chemistry and clinical analysis. Since most analytical instrumentation is comparative, it requires a sample of known composition (reference material) for accurate calibration. These reference materials are produced under stringent manufacturing procedures and differ from laboratory reagents in their certification and the traceability of the data provided.
Quality management systems involving laboratory accreditation under national and international accreditation/certification standards such as ISO/IEC 17025 require metrological traceability to Certified Reference Materials (where possible) when using reference materials for calibration.
Whilst Certified Reference Materials are preferred where available, their availability is limited. Reference Materials that do not meet all the criteria for certified reference materials are more widely available: the principal difference is the additional evidence of metrological traceability and statement of measurement uncertainty provided on the certificate for certified reference materials. | 3 | Analytical Chemistry |
The Eagle effect, Eagle phenomenon, or paradoxical zone phenomenon, named after Harry Eagle who first described it, originally referred to the paradoxically reduced antibacterial effect of penicillin at high doses, though recent usage generally refers to the relative lack of efficacy of beta lactam antibacterial drugs on infections having large numbers of bacteria. The former effect is paradoxical because the effectiveness of an antibiotic generally rises with increasing drug concentration.
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The Arc system connects the electron transport chain to regulation of certain genes, allowing aerobic respiration to occur in the presence of oxygen and fermentation to take place when no oxygen is present. This is done through the connection of ArcB with quinones from the electron transport chain. Oxidized quionones, from the electron transport chain, act to inhibit autophosphorylation of ArcB during aerobic respiration. This in turn prevents the phosphorylation of ArcA, turning off the activated operons.
It has been determined that the Arc system regulates as many as 30 genes, with repression of the following examples: cytochrome o oxidase, cytochrome d oxidase, and various gluconeogenic enzymes, such as for the glyoxylate cycle, and fatty acid oxidation. It also induces the expression of Pyruvate formate lyase.
One of the major genes controlled is the sdh-lacZ operon. This, in part, codes for the synthesis of succinate dehydrogenase, a key element in the TCA cycle. ArcA turns expression of the sdh-lacZ operon off in the presence of oxygen, stopping procession of the TCA cycle. It also activates lctD and pyruvate formate lyase. These genes are critical in the lactic acid fermentation process. They are activated in anoxic conditions to allow the cell to continue producing ATP and growing even in less favorable conditions. ArcA represses many of the other enzymes involved in the TCA cycle as well including flavoprotein dehydrogenases, and ubiquinones oxidases. It also represses enzymes involved in synthesizing glyoxylate, some dehydrognases used in aerobic growth, and enzymes involved in fatty acid oxidation. Activated operons include genes for the pyruvate formate-lyase pathway and enzymes involved in synthesizing cobalamin.
Another of the genes effected codes for the production of certain cytochromes. ArcA respresses cytochrome bo oxidase and activates cytochrome bd oxidase. Cytochromes are classified based on the hemes they possess, in this case cytochrome bo possesses a heme c while cytochorme bd oxidase psoseses a heme d. Cytochormes bo oxidase is one of the main electron transporters during the elctron transport chain of aerobic respiration. It has the ability to reduce most organic compounds found in cellular metabolism. Cytochrome bd oxidase is activated in anaerobic conditions. It has a higher affinity for oxygen than cytochrome bo oxidase which may be useful to cells in anoxic conditions. | 1 | Biochemistry |
Tertiary (3°) phosphines, with the formula RP, are traditionally prepared by alkylation of phosphorus trichloride using Grignard reagents or related organolithium compounds:
:3RMgX + PCl → PR + 3MgX
In the case of trimethylphosphine, triphenyl phosphite is used in place of the highly electrophilic PCl:
: 3 CHMgBr + P(OCH) → P(CH) + 3 CHOMgBr
Slightly more elaborate methods are employed for the preparation of unsymmetrical tertiary phosphines, with the formula RR'P. The use of organophosphorus-based nucleophiles is typical. For example, lithium diphenylphosphide is readily methylated with methyl iodide to give methyldiphenylphosphine:
:LiiP(CH) + CHI → CHP(CH) + LiI
Phosphine is a precursor to some tertiary phosphines by hydrophosphination of alkenes. For example, in the presence of basic catalysts PH adds of Michael acceptors such as acrylonitrile:
:PH + 3 CH=CHZ → P(CHCHZ) (Z = NO, CN, C(O)NH)
Tertiary phosphines of the type PRR′R″ are "P-chiral" and optically stable.
From the commercial perspective, the most important phosphine is triphenylphosphine, several million kilograms being produced annually. It is prepared from the reaction of chlorobenzene, PCl, and sodium. Phosphines of a more specialized nature are usually prepared by other routes. | 0 | Organic Chemistry |
One of the most well known epigenetic mechanisms that proline isomerization plays a role in is the modification of histone tails, specifically those of histone H3. Fpr4 is a PPIase, in the FK507BP group, that exhibits catalytic activity at the proline positions 16, 30, and 38 (also written P16, P30, and P38 respectively) on the N-terminal region of histone H3 in Saccharomyces cerevisiae. Fpr4s binding affinity is strongest at the P38 site, followed by P30 and then P16. However the catalytic efficiency, or the increase in isomerization rates, is highest at P16 and P30 equally, followed by P38 which exhibits a very small change in isomerization rates with the binding of Fpr4. Histone H3 has an important lysine residue at the 36 position (also written K36) on the N-terminal tail which can be methylated by Set2, a methyltransferase. Methylation of K36 is key to normal transcription elongation. Due to P38s proximity to K36, cross-talk between P38 isomerization and K36 methylation can occur. This means that isomer changes at the P38 position can affect methylation at the K36 position. In the cis position, P38 shifts the histone tail closer to the DNA, crowding the area around the tail. This can cause a decrease the ability of proteins to bind to the DNA and to the histone tail, including preventing Set2 from methylating K36. Also, this tail movement can increase the number interactions between the histone tail and the DNA, increasing likelihood of nucleosome formation and potentially leading to the creation of higher-order chromatin structure. In trans, P38 leads to the opposite effects: allowing for Set2 to methylate K36. Set2 is only affected by isomerization of P38 when creating a trimethylated K36 (commonly written as K36me3), however, and not K36me2. Fpr4 also binds to P32 in H4, though its effects are minimal.
In mammalian cells, the isomerization of H3P30 interacts with the phosphorylation of H3S28 (serine in the 28 position of histone H3) and the methylation of H3K27. hFKBP25 is a PPIase that is a homolog for Fpr4 in mammalian cells and is found to commonly be associated with the presence of HDACs. Cyp33 is a cyclophilin that has the ability to isomerize H3 proline residues at P16 and P30 positions. Histones H2A and H2B also have multiple proline residues near amino acids that when modified affect the activity surrounding the histone. | 4 | Stereochemistry |
Mice can distinguish close relatives from more distantly related individuals on the basis of scent signals, which enables them to avoid mating with close relatives and minimizes deleterious inbreeding.
In addition to mice, two species of bumblebee, in particular Bombus bifarius and Bombus frigidus, have been observed to use pheromones as a means of kin recognition to avoid inbreeding. For example, B. bifarius males display "patrolling" behavior in which they mark specific paths outside their nests with pheromones and subsequently "patrol" these paths. Unrelated reproductive females are attracted to the pheromones deposited by males on these paths, and males that encounter these females while patrolling can mate with them. Other bees of the Bombus species are found to emit pheromones as precopulatory signals, such as Bombus lapidarius. | 1 | Biochemistry |
The term spiral separator can refer to either a device for separating slurry components by density (wet spiral separators), or for a device for sorting particles by shape (dry spiral separators). | 3 | Analytical Chemistry |
Survivin is a member of the IAP family of antiapoptotic proteins. It is shown to be conserved in function across evolution as homologues of the protein are found both in vertebrates and invertebrates. The first members of the IAPs identified were from the baculovirus IAPs, Cp-IAP and Op-IAP, which bind to and inhibit caspases as a mechanism that contributes to its efficient infection and replication cycle in the host. Later, five more human IAPs that included XIAP, c-IAPl, C-IAP2, NAIP, and survivin were discovered. Survivin, like the others, was discovered by its structural homology to IAP family of proteins in human B-cell lymphoma. The human IAPs, XIAP, c-IAPl, C-IAP2 have been shown to bind to caspase-3 and -7, which are the effector caspases in the signaling pathway of apoptosis. It is not known with absolute certainty though, how the IAPs inhibit apoptosis mechanistically at the molecular level.
A common feature that is present in all IAPs in the presence of a BIR (Baculovirus IAP Repeat, a ~70 amino acid motif) in one to three copies. It was shown by Tamm et al. that knocking out BIR2 from XIAP was enough to cause a loss of function in terms of XIAPs ability to inhibit caspases. This gives the implication that it is within these BIR motifs that contains the anti-apoptotic function of these IAPs. Survivins one BIR domain shows a similar sequence compared to that of XIAPs BIR domains. | 1 | Biochemistry |
In quantum mechanics, a triplet state, or spin triplet, is the quantum state of an object such as an electron, atom, or molecule, having a quantum spin S = 1. It has three allowed values of the spins projection along a given axis m' = −1, 0, or +1, giving the name "triplet".
Spin, in the context of quantum mechanics, is not a mechanical rotation but a more abstract concept that characterizes a particle's intrinsic angular momentum. It is particularly important for systems at atomic length scales, such as individual atoms, protons, or electrons.
A triplet state occurs in cases where the spins of two unpaired electrons, each having spin s = 1/2, align to give S = 1, in contrast to the more common case of two electrons aligning oppositely to give S = 0, a spin singlet. Most molecules encountered in daily life exist in a singlet state because all of their electrons are paired, but molecular oxygen is an exception. At room temperature, O exists in a triplet state, which can only undergo a chemical reaction by making the forbidden transition into a singlet state. This makes it kinetically nonreactive despite being thermodynamically one of the strongest oxidants. Photochemical or thermal activation can bring it into the singlet state, which makes it kinetically as well as thermodynamically a very strong oxidant.
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The Lely method, also known as the Lely process or Lely technique, is a crystal growth technology used for producing silicon carbide crystals for the semiconductor industry. The patent for this method was filed in the Netherlands in 1954 and in the United States in 1955 by Jan Anthony Lely of Philips Electronics. The patent was subsequently granted on 30 September 1958, then was refined by D. R. Hamilton et al. in 1960, and by V. P. Novikov and V. I. Ionov in 1968. | 3 | Analytical Chemistry |
The temperature-entropy conjugate pair is concerned with the transfer of energy, especially for a closed system.
* An isothermal process occurs at a constant temperature. An example would be a closed system immersed in and thermally connected with a large constant-temperature bath. Energy gained by the system, through work done on it, is lost to the bath, so that its temperature remains constant.
* An adiabatic process is a process in which there is no matter or heat transfer, because a thermally insulating wall separates the system from its surroundings. For the process to be natural, either (a) work must be done on the system at a finite rate, so that the internal energy of the system increases; the entropy of the system increases even though it is thermally insulated; or (b) the system must do work on the surroundings, which then suffer increase of entropy, as well as gaining energy from the system.
* An isentropic process is customarily defined as an idealized quasi-static reversible adiabatic process, of transfer of energy as work. Otherwise, for a constant-entropy process, if work is done irreversibly, heat transfer is necessary, so that the process is not adiabatic, and an accurate artificial control mechanism is necessary; such is therefore not an ordinary natural thermodynamic process. | 7 | Physical Chemistry |
TCE is also used in the manufacture of a range of fluorocarbon refrigerants such as 1,1,1,2-tetrafluoroethane more commonly known as HFC 134a. TCE was also used in industrial refrigeration applications due to its high heat transfer capabilities and its low-temperature specification. | 2 | Environmental Chemistry |
Goss completed her undergraduate studies in Chemistry at the University of Durham in 1997. Under the supervision of Prof. David O'Hagan, Goss completed her Ph.D. studying the biosynthesis of various natural products including the stereochemistry of enzymatic fluorination in fluoroacetate biosynthesis. | 0 | Organic Chemistry |
Capnellene-8β,10α-diol and its acylated derivatives exhibit significant cytotoxicity in vitro against cervical epitheloid carcinoma (HeLa, oral epidermoid (KB), medulloblastoma (Daoy) and colon adenocarcinoma (WiDr) human tumor cell lines. The diol was also effective against human leukemia, renal leiomyoblastoma, colon and breast cancer cell lines. In the same study, capnellene-8β-ol demonstrated selective toxicity for the renal leiomyoblastoma and ovarian cancer cell lines, while 3β-acetoxycapnellene-8β,10α,14β-triol was active against leukemia cell lines. The antitumor properties of capnellene derivatives have yet to be explored in vivo. | 0 | Organic Chemistry |
One feature of enzymes is their high specificity. They are specific on a singular substrate, reaction or both together, that means, that the enzymes can catalyze all reactions wherein the substrate can experience.
The enzyme cholesterol 7 alpha hydroxylase catalyzes the reaction that converts cholesterol into cholesterol 7 alpha hydroxylase reducing and oxidizing that molecule. | 1 | Biochemistry |
The preparation of ceramic specimens for microstructural analysis consists of five broad steps: sawing, embedding, grinding, polishing and etching. The tools and consumables for ceramographic preparation are available worldwide from metallography equipment vendors and laboratory supply companies. | 8 | Metallurgy |
Polymerase chain reaction itself is the process used to amplify DNA samples, via a temperature-mediated DNA polymerase. The products can be used for sequencing or analysis, and this process is a key part of many genetics research laboratories, along with uses in DNA fingerprinting for forensics and other human genetic cases. Conventional PCR requires primers complementary to the termini of the target DNA. The amount of product from the PCR increases with the number of temperature cycles that the reaction is subjected to. A commonly occurring problem is primers binding to incorrect regions of the DNA, giving unexpected products. This problem becomes more likely with an increased number of cycles of PCR. | 1 | Biochemistry |
*Group 2 elements calcium, strontium, and barium can all form octacarbonyl complexes M(CO) (M = Ca, Sr, Ba). The compounds were characterized in cryogenic matrices by vibrational spectroscopy and in gas phase by mass spectrometry.
*Group 4 elements with 4 valence electrons are expected to form heptacarbonyls; while these are extremely rare, substituted derivatives of Ti(CO) are known.
*Group 5 elements with 5 valence electrons, again are subject to steric effects that prevent the formation of M–M bonded species such as V(CO), which is unknown. The 17-VE V(CO) is however well known.
*Group 6 elements with 6 valence electrons form hexacarbonyls Cr(CO), Mo(CO), W(CO), and Sg(CO). Group 6 elements (as well as group 7) are also well known for exhibiting the cis effect (the labilization of CO in the cis position) in organometallic synthesis.
*Group 7 elements with 7 valence electrons form pentacarbonyl dimers Mn(CO), Tc(CO), and Re(CO).
*Group 8 elements with 8 valence electrons form pentacarbonyls Fe(CO), Ru(CO) and Os(CO). The heavier two members are unstable, tending to decarbonylate to give Ru(CO), and Os(CO). The two other principal iron carbonyls are Fe(CO) and Fe(CO).
*Group 9 elements with 9 valence electrons and are expected to form tetracarbonyl dimers M(CO). In fact the cobalt derivative of this octacarbonyl is the only stable member, but all three tetramers are well known: Co(CO), Rh(CO), Rh(CO), and Ir(CO). Co(CO) unlike the majority of the other 18 VE transition metal carbonyls is sensitive to oxygen.
*Group 10 elements with 10 valence electrons form tetracarbonyls such as Ni(CO). Curiously Pd(CO) and Pt(CO) are not stable. | 0 | Organic Chemistry |
There are a number of distinct methods of holding the precursors together prior to the ultimate ring-closing reaction in a template-directed catenane synthesis. Each noncovalent approach to catenane formation results in what can be considered different families of catenanes.
Another family of catenanes are called pretzelanes or bridged [2]catenanes after their likeness to pretzels with a spacer linking the two macrocycles. In one such system one macrocycle is an electron deficient oligo Bis-bipyridinium ring and the other cycle is crown ether cyclophane based on para phenylene or naphthalene. X-ray diffraction shows that due to pi-pi interactions the aromatic group of the cyclophane is held firmly inside the pyridinium ring. A limited number of (rapidly interchanging) conformers exist for this type of compound.
In handcuff-shaped catenanes, two connected rings are threaded through the same ring. The bis-macrocycle (red) contains two phenanthroline units in a crown ether chain. The interlocking ring is self-assembled when two more phenanthroline units with alkene arms coordinate through a copper(I) complex followed by a metathesis ring closing step. | 6 | Supramolecular Chemistry |
Methods for predicting liquid properties can be organized by their "scale" of description, that is, the length scales and time scales over which they apply.
*Macroscopic methods use equations that directly model the large-scale behavior of liquids, such as their thermodynamic properties and flow behavior.
*Microscopic methods use equations that model the dynamics of individual molecules.
*Mesoscopic methods fall in between, combining elements of both continuum and particle-based models. | 7 | Physical Chemistry |
Darwins Black Box: The Biochemical Challenge to Evolution (1996; second edition 2006) is a book by Michael J. Behe, a professor of biochemistry at Lehigh University in Pennsylvania and a senior fellow of the Discovery Institutes Center for Science and Culture. In the book Behe presents his notion of irreducible complexity and argues that its presence in many biochemical systems therefore indicates that they must be the result of intelligent design rather than evolutionary processes. In 1993, Behe had written a chapter on blood clotting in Of Pandas and People, presenting essentially the same arguments but without the name "irreducible complexity," which he later presented in very similar terms in a chapter in Darwins Black Box. Behe later agreed that he had written both and agreed to the similarities when he defended intelligent design at the Kitzmiller v. Dover Area School District' trial.
The book has received highly critical reviews by many scientists, arguing that the assertions made by Behe fail with logical scrutiny and amount to pseudoscience. For example, in a review for Nature, Jerry Coyne panned the book for what he saw as usage of quote mining and spurious ad hominem attacks. The New York Times also, in a critique written by Richard Dawkins, condemned the book for having promoted discredited arguments. Despite this, the book has become a commercial success, and, as a bestseller, it received a mostly supportive review from Publishers Weekly, which described it as having a "spirited, witty critique of neo-Darwinian thinking" that may "spark interest." The politically conservative magazine National Review also voted Darwins Black Box' one of their top 100 non-fiction books of the century, using a panel that included Discovery Institute member George Gilder. | 1 | Biochemistry |
In chemistry, the molar absorption coefficient or molar attenuation coefficient () is a measurement of how strongly a chemical species absorbs, and thereby attenuates, light at a given wavelength. It is an intrinsic property of the species. The SI unit of molar absorption coefficient is the square metre per mole (), but in practice, quantities are usually expressed in terms of ⋅cm or L⋅mol⋅cm (the latter two units are both equal to ). In older literature, the cm/mol is sometimes used; 1 M⋅cm equals 1000 cm/mol. The molar absorption coefficient is also known as the molar extinction coefficient and molar absorptivity, but the use of these alternative terms has been discouraged by the IUPAC. | 3 | Analytical Chemistry |
A separating funnel takes the shape of a cone with a hemispherical end. It has a stopper at the top and stopcock (tap), at the bottom. Separating funnels used in laboratories are typically made from borosilicate glass and their taps are made from glass or PTFE. Typical sizes are between 30 mL and 3 L. In industrial chemistry they can be much larger and for much larger volumes centrifuges are used. The sloping sides are designed to facilitate the identification of the layers. The tap-controlled outlet is designed to drain the liquid out of the funnel. On top of the funnel there is a standard taper joint which fits with a ground glass or Teflon stopper.
To use a separating funnel, the two phases and the mixture to be separated in solution are added through the top with the stopcock at the bottom closed. The funnel is then closed and shaken gently by inverting the funnel multiple times; if the two solutions are mixed together too vigorously emulsions will form. The funnel is then inverted and the stopcock carefully opened to release excess vapor pressure. The separating funnel is set aside to allow for the complete separation of the phases. The top and the bottom stopcock are then opened and the lower phase is released by gravitation. The top must be opened while releasing the lower phase to allow pressure equalization between the inside of the funnel and the atmosphere. When the bottom layer has been removed, the stopcock is closed and the upper layer is poured out through the top into another container. | 3 | Analytical Chemistry |
The Dortmund Data Bank was founded in the 1970s at the University of Dortmund in Germany. The original reason for starting a vapor–liquid phase equilibria data collection was the development of the group contribution method UNIFAC which allows to estimate vapor pressures of mixtures.
The DDB has since been extended to many other properties and has increased dramatically in size also because of intensive (German) government aid. The funding has ended and the further development and maintenance is performed by DDBST GmbH, a company founded by members of the industrial chemistry chair of the Carl von Ossietzky University of Oldenburg, Germany.
Additional contributors are the DECHEMA, the FIZ CHEMIE (Berlin), the Technical University in Tallinn, and others. | 7 | Physical Chemistry |
Mollapour is married to Dimitra Bourboulia, PhD, Associate Professor, Assistant Dean for Undergraduate and Graduate Medical Education Research, and Director for the Office of Research for Medical Students, at SUNY Upstate Medical University. | 1 | Biochemistry |
CoQ is a component of the mitochondrial electron transport chain (ETC), where it plays a role in oxidative phosphorylation, a process required for the biosynthesis of adenosine triphosphate, the primary energy source of cells.
CoQ is a lipophilic molecule that is located in all biological membranes of human body and serves as a component for the synthesis of ATP and is a life-sustaining cofactor for the three complexes (complex I, complex II, and complex III) of the ETC in the mitochondria. CoQ has a role in the transport of protons across lysosomal membranes to regulate pH in lysosome functions.
The mitochondrial oxidative phosphorylation process takes place in the inner mitochondrial membrane of eukaryotic cells. This membrane is highly folded into structures called cristae, which increase the surface area available for oxidative phosphorylation. CoQ plays a role in this process as an essential cofactor of the ETC located in the inner mitochondrial membrane and serves the following functions:
* electron transport in the mitochondrial ETC, by shuttling electrons from mitochondrial complexes like nicotinamide adenine dinucleotide (NADH), ubiquinone reductase (complex I), and succinate ubiquinone reductase (complex II), the fatty acids and branched-chain amino acids oxidation (through flavin-linked dehydrogenases) to ubiquinol–cytochrome-c reductase (complex III) of the ETC: CoQ participates in fatty acid and glucose metabolism by transferring electrons generated from the reduction of fatty acids and glucose to electron acceptors;
* antioxidant activity as a lipid-soluble antioxidant together with vitamin E, scavenging reactive oxygen species and protecting cells against oxidative stress, inhibiting the oxidation of proteins, DNA, and use of vitamin E.
CoQ also may influence immune response by modulating the expression of genes involved in inflammation. | 1 | Biochemistry |
The fundamental resolution equation is used in chromatography to help relate adjustable chromatographic parameters to resolution, and is as follows:
R = [N/4][(α-1)/α][k/(1+k)], where
N = Number of theoretical plates
α = Selectivity Term = k/k
The [N/4] term is the column factor, the [(α-1)/α] term is the thermodynamic factor, and the [k/(1+k)] term is the retention factor. The 3 factors are not completely independent, but they are very close, and can be treated as such.
So what does this mean? It means that to increase resolution of two peaks on a chromatogram, one of the three terms of the equation need to be modified.
1) N can be increased by lengthening the column (least effective, as doubling the column will get a 2 or 1.44x increase in resolution).
2) Increasing k' also helps. This can be done by lowering the column temperature in G.C., or by choosing a weaker mobile phase in L.C. (moderately effective)
3) Changing α is the most effective way of increasing resolution. This can be done by choosing a stationary phase that has a greater difference between k and k. It can also be done in L.C. by using pH to invoke secondary equilibria (if applicable).
The fundamental resolution equation is derived as follows:
For two closely spaced peaks, ω = ω, and σ = σ
so R = (t - t)/ω = (t - t)/4σ
Where t and t are the retention times of two separate peaks.
Since N = [(t)/σ], then σ = t/ N
Using substitution, R = N[(t - t)/4t] = (N/4)(1 - t/t)
Now using the following equations and solving for t and t
k = (t - t)/t ; t = t(k + 1)
k = (t - t)/t ; t = t(k + 1)
Substituting again and you get:
R = [N/4][1 - (k + 1)/(k + 1] = [N/4][(k - k)/(1 + k')]
And finally substituting once more α = k/k and you get the Fundamental Resolution Equation:
R = [N/4][(α-1)/α][k/(1+k)] | 3 | Analytical Chemistry |
Reversed-phase liquid chromatography (RP-LC) is a mode of liquid chromatography in which non-polar stationary phase and polar mobile phases are used for the separation of organic compounds. The vast majority of separations and analyses using high-performance liquid chromatography (HPLC) in recent years are done using the reversed phase mode. In the reversed phase mode, the sample components are retained in the system the more hydrophobic they are.
The factors affecting the retention and separation of solutes in the reversed phase chromatographic system are as follows:
a. The chemical nature of the stationary phase, i.e., the ligands bonded on its surface, as well as their bonding density, namely the extent of their coverage.
b. The composition of the mobile phase. Type of the bulk solvents whose mixtures affect the polarity of the mobile phase, hence the name modifier for a solvent added to affect the polarity of the mobile phase.
C. Additives, such as buffers, affect the pH of the mobile phase, which affect the ionization state of the solutes and their polarity.
In order to retain the organic components in mixtures, the stationary phases, packed within columns, consist of a hydrophobic substrates, bonded to the surface of porous silica-gel particles in various geometries (spheric, irregular), at different diameters (sub-2, 3, 5, 7, 10 um), with varying pore diameters (60, 100, 150, 300, A). The particle's surface is covered by chemically bonded hydrocarbons, such as C3, C4, C8, C18 and more. The longer the hydrocarbon associated with the stationary phase, the longer the sample components will be retained. Some stationary phases are also made of hydrophobic polymeric particles, or hybridized silica-organic groups particles, for method in which mobile phases at extreme pH are used. Most current methods of separation of biomedical materials use C-18 columns, sometimes called by trade names, such as ODS (octadecylsilane) or RP-18.
The mobile phases are mixtures of water and polar organic solvents, the vast majority of which are methanol and acetonitrile. These mixtures usually contain various additives such as buffers (acetate, phosphate, citrate), surfactants (alkyl amines or alkyl sulfonates) and special additives (EDTA). The goal of using supplements of one kind or another is to increase efficiency, selectivity, and control solute retention. | 3 | Analytical Chemistry |
Branched chain fatty acids are usually saturated and are found in two distinct families: the iso-series and anteiso-series. It has been found that Actinomycetales contain unique branch-chain fatty acid synthesis mechanisms, including that which forms tuberculosteric acid. | 1 | Biochemistry |
Historically, displacement chromatography was applied to preparative separations of amino acids and rare earth elements and has also been investigated for isotope separation. | 3 | Analytical Chemistry |
Silicification of woods usually occur in terrestrial conditions, but sometimes it could be done in aquatic environments. Surface water silicification can be done through the precipitation of silica in silica-enriched hot springs. On the northern coast of central Japan, the Tateyama hot spring has a high silica content that contributes to the silicification of nearby fallen woods and organic materials. Silica precipitates rapidly out of the fluids and opal is the main form of silica. With a temperature of around 70°C and a pH value of around 3, the opal deposited is composed of silica spheres of different sizes arranged randomly. | 9 | Geochemistry |
Leaving alone remote antiquity and starting with Imperial Rome, the working of bronze, inspired probably by conquered Greece, is clearly seen. There are ancient bronze doors in the Temple of Romulus in the Roman Forum; others from the baths of Caracalla are in the Lateran Basilica, which also contains four fine gilt bronze fluted columns of the Corinthian order. The Naples Museum contains a large collection of domestic utensils of bronze, recovered from the buried towns of Pompeii and Herculaneum, which show a high degree of perfection in the working of the metal, as well as a wide application of its use. A number of moorings in the form of finely modelled animal heads, made in the 1st century AD, and recovered from Lake Nemi in the Alban hills some years ago, show a further acquaintance with the skilful working of this metal. The throne of Dagobert in the Bibliothèque Nationale, Paris, appears to be a Roman bronze curule chair, with back and part of the arms added by the Abbot Suger in the 12th century.
Byzantium, from the time when Constantine made it the seat of empire, in the early part of the 4th century, was for 1,000 years renowned for its works in metal. Its position as a trade centre between East and West attracted all the finest work provided by the artistic skills of craftsmen from Syria, Egypt, Persia, Asia Minor and the northern shores of the Black Sea, and for 400 years, until the beginning of the Iconoclastic period in the first half of the 8th century, its output was enormous. Several Italian churches still retain bronze doors cast in Constantinople in the later days of the Eastern Empire, such as those presented by the members of the Pantaleone family, in the latter half of the 11th century, to the churches at Amalfi, Monte Cassino, Atrani and Monte Gargano. Similar doors are at Salerno; and St Mark's, Venice, also has doors of Greek origin. | 8 | Metallurgy |
In geometry, a Euclidean plane isometry is an isometry of the Euclidean plane, or more informally, a way of transforming the plane that preserves geometrical properties such as length. There are four types: translations, rotations, reflections, and glide reflections (see below ).
The set of Euclidean plane isometries forms a group under composition: the Euclidean group in two dimensions. It is generated by reflections in lines, and every element of the Euclidean group is the composite of at most three distinct reflections. | 3 | Analytical Chemistry |
Humic substances in soils and sediments can be divided into three main fractions: humic acids, fulvic acids, and humin.
Humic and fulvic acids are extracted from soil and other solid phase sources into a strongly basic aqueous solution of sodium hydroxide or potassium hydroxide.
*Humic acids are precipitated from this solution by adjusting the pH to 1 with hydrochloric acid.
*The alcohol-soluble portion of humic fraction is, in general, named ulmic acid.
** So-called "gray humic acids" (GHA) are soluble in low-ionic-strength alkaline media.
** "Brown humic acids" (BHA) are soluble in alkaline conditions independent of ionic strength
* Fulvic acids is left in solution at pH 1. They remain soluble independent of pH and ionic strength.
* Humin is insoluble in dilute alkali.
The International Humic Substances Society (IHSS) advocates the use of standard laboratory methods for preparation of humic and fulvic acids. Humic substances are extracted from soil and other solid sources using NaOH, the humic acids are then precipitated at pH 1, and the soluble fraction is treated on a resin column to separate fulvic acid components from other acid soluble compounds. Humic acid plus fulvic acid are extracted from natural waters using a resin column after microfiltration and acidification to pH 2. The humic materials are eluted from the column with NaOH and humic acid is precipitated at pH 1. After adjusting the pH to 2 the fulvic acid is separated from other acid soluble compounds using a resin column as with solid phase sources. An analytical method for quantifying humic acid and fulvic acid in commercial ores and products, has been developed based on the IHSS humic acid and fulvic acid preparation methods,
Extracted humic acid not a single acid; rather, it is a complex mixture of many different acids containing carboxyl and phenolate groups so that the mixture behaves functionally as a dibasic acid or, occasionally, as a tribasic acid. Commercial humic acid used to amend soil is manufactured using these same well established procedures. Humic acids can form complexes with ions that are commonly found in the environment creating humic colloids.
As a nutrition supplement, fulvic acid can be found in a liquid form as a component of mineral colloids. Fulvic acids are poly-electrolytes and are unique colloids that diffuse easily through membranes, whereas all other colloids do not.
A sequential chemical fractionation called Humeomics can be used to isolate more homogeneous humic fractions and determine their molecular structures by advanced spectroscopic and chromatographic methods. Substances identified in humic extracts and directly in soil include mono-, di-, and tri-hydroxycarboxylic acids, fatty acids, dicarboxylic acids, linear alcohols, phenolic acids, terpenoids, carbohydrates, and amino acids. | 9 | Geochemistry |
Cobalt extraction refers to the techniques used to extract cobalt from its ores and other compound ores. Several methods exist for the separation of cobalt from copper and nickel. They depend on the concentration of cobalt and the exact composition of the ore used. | 8 | Metallurgy |
Two-metal dual activation represents the combination of the enolate activation mode and the alkyne activation mode into a single reaction system. Generally, a hard, oxophilic metal (K, Na, Ag) activates the enolate oxygen, while a soft, carbophilic metal (Pd, Cu, Mo) coordinates with the alkyne. In some instances, however, the precise role of each metal is unclear. For example, in a 2005 study Toste et al. found that treatment of an alkynyl-tethered β-ketoester with a Pd(II) phosphine complex and Yb(OTf) effected asymmetric cyclization to the corresponding cyclopentane. It is proposed that a Pd-enolate adds into a Yb-activated alkyne, though there is also precedent for Pd activation of alkynes. | 0 | Organic Chemistry |
Much like β-oxidation, straight-chain fatty acid synthesis occurs via the six recurring reactions shown below, until the 16-carbon palmitic acid is produced.
The diagrams presented show how fatty acids are synthesized in microorganisms and list the enzymes found in Escherichia coli. These reactions are performed by fatty acid synthase II (FASII), which in general contain multiple enzymes that act as one complex. FASII is present in prokaryotes, plants, fungi, and parasites, as well as in mitochondria.
In animals, as well as some fungi such as yeast, these same reactions occur on fatty acid synthase I (FASI), a large dimeric protein that has all of the enzymatic activities required to create a fatty acid. FASII is less efficient than FASI; however, it allows for the formation of more molecules, including "medium-chain" fatty acids via early chain termination.
Once a 16:0 carbon fatty acid has been formed, it can undergo a number of modifications, resulting in desaturation and/or elongation. Elongation, starting with stearate (18:0), is performed mainly in the ER by several membrane-bound enzymes. The enzymatic steps involved in the elongation process are principally the same as those carried out by FAS, but the four principal successive steps of the elongation are performed by individual proteins, which may be physically associated.
Note that during fatty synthesis the reducing agent is NADPH, whereas NAD is the oxidizing agent in beta-oxidation (the breakdown of fatty acids to acetyl-CoA). This difference exemplifies a general principle that NADPH is consumed during biosynthetic reactions, whereas NADH is generated in energy-yielding reactions. (Thus NADPH is also required for the synthesis of cholesterol from acetyl-CoA; while NADH is generated during glycolysis.) The source of the NADPH is two-fold. When malate is oxidatively decarboxylated by "NADP-linked malic enzyme" to form pyruvate, and NADPH are formed. NADPH is also formed by the pentose phosphate pathway which converts glucose into ribose, which can be used in synthesis of nucleotides and nucleic acids, or it can be catabolized to pyruvate. | 1 | Biochemistry |
In the lin⊥lin configuration cooling is achieved via a Sisyphus effect. Consider two counterpropagating electromagnetic waves with equal amplitude and orthogonal linear polarizations and , where k is the wavenumber . The superposition of and is given as:
Introducing a new pair of coordinates and the field can be written as:
The polarization of the total field changes with z. For example: we see that at the field is linearly polarized along , at the field has left circular polarization, at the field is linearly polarized along , at the field has right circular polarization, and at the field is again linearly polarized along .
Consider an atom interacting with the field detuned below the transition from atomic states and (). The variation of the polarization along z results in a variation in the light shifts of the atomic Zeeman sublevels with z. The Clebsch-Gordan coefficient connecting the state to the state is 3 times larger than connecting the state to the state. Thus for polarization the light shift is three times larger for the state than for the state. The situation is reversed for polarization, with the light shift being three times larger for the state than the state. When the polarization is linear, there is no difference in the light shifts between the two states. Thus the energies of the states will oscillate in z with period .
As an atom moves along z, it will be optically pumped to the state with the largest negative light shift. However, the optical pumping process takes some finite time . For field wavenumber k and atomic velocity v such that , the atom will travel mostly uphill as it moves along z before being pumped back down to the lowest state. In this velocity range, the atom travels more uphill than downhill and gradually loses kinetic energy, lowering its temperature. This is called the Sisyphus effect after the mythological Greek character. Note that this initial condition for velocity requires the atom to be cooled already, for example through Doppler cooling. | 7 | Physical Chemistry |
A fire test can be conducted to determine the degree of flammability. Test standards used to make this determination but are not limited to the following:
* Underwriters Laboratories [http://ulstandards.ul.com/standard/?id=94&edition=6&doctype=ulstd UL 94 Flammability Testing]
* International Electrotechnical Commission IEC 60707, 60695-11-10 and 60695-11-20
* International Organization for Standardization ISO 9772 and 9773.
* National Fire Protection Association [http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=287 NFPA 287 Standard Test Methods for Measurement of Flammability of Materials in Cleanrooms Using a Fire Propagation Apparatus (FPA)]
* [http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=701 NFPA 701: Standard Methods of Fire Tests for Flame Propagation of Textiles and Films]
* [http://www.nfpa.org/aboutthecodes/AboutTheCodes.asp?DocNum=850 NFPA 850: Recommended Practice for Fire Protection for Electric Generating Plants and High Voltage Direct Current Converter Stations] | 7 | Physical Chemistry |
Light scattering spectroscopy (LSS) is a spectroscopic technique typically used to evaluate morphological changes in epithelial cells in order to study mucosal tissue and detect early cancer and precancer.
Light scattering spectroscopy relies upon elastic scattering of photons reflected from the epithelium. Most of the signal is generated by light scattering from small intracellular structures, but larger intracellular structures, such as nuclei, also scatter light, with their relative contribution increasing in the backscatter direction. As changes in the morphology of epithelial cells are hallmarks of pre-cancer and early cancer, LSS can be used for early cancer diagnosis.
In addition to photons backscattering from epithelial cells, a major portion of photons penetrates the epithelium, reaching optically turbid connective tissue where they are scattered multiple times and partially absorbed by hemoglobin. As a result, it is not possible to measure single backscattering events directly in human tissue, with polarization gating and spatial gating well-suited for endoscopy applications. | 7 | Physical Chemistry |
Due to their high reactivity, most metals were not discovered until the 19th century. A method for extracting aluminium from bauxite was proposed by Humphry Davy in 1807, using an electric arc. Although his attempts were unsuccessful, by 1855 the first sales of pure aluminium reached the market. However, as extractive metallurgy was still in its infancy, most aluminium extraction-processes produced unintended alloys contaminated with other elements found in the ore; the most abundant of which was copper. These aluminium-copper alloys (at the time termed "aluminum bronze") preceded pure aluminium, offering greater strength and hardness over the soft, pure metal, and to a slight degree were found to be heat treatable. However, due to their softness and limited hardenability these alloys found little practical use, and were more of a novelty, until the Wright brothers used an aluminium alloy to construct the first airplane engine in 1903. During the time between 1865 and 1910, processes for extracting many other metals were discovered, such as chromium, vanadium, tungsten, iridium, cobalt, and molybdenum, and various alloys were developed.
Prior to 1910, research mainly consisted of private individuals tinkering in their own laboratories. However, as the aircraft and automotive industries began growing, research into alloys became an industrial effort in the years following 1910, as new magnesium alloys were developed for pistons and wheels in cars, and pot metal for levers and knobs, and aluminium alloys developed for airframes and aircraft skins were put into use. | 8 | Metallurgy |
Under stress conditions (e.g. water deficit) oxalate released from calcium oxalate crystals is converted to CO by an oxalate oxidase enzyme and the produced CO can support the Calvin cycle reactions. Reactive hydrogen peroxide (HO), the byproduct of oxalate oxidase reaction, can be neutralized by catalase. | 5 | Photochemistry |
Cytochromes are proteins that contain iron. They are found in two very different environments.
Some cytochromes are water-soluble carriers that shuttle electrons to and from large, immobile macromolecular structures imbedded in the membrane. The mobile cytochrome electron carrier in mitochondria is cytochrome c. Bacteria use a number of different mobile cytochrome electron carriers.
Other cytochromes are found within macromolecules such as Complex III and Complex IV. They also function as electron carriers, but in a very different, intramolecular, solid-state environment.
Electrons may enter an electron transport chain at the level of a mobile cytochrome or quinone carrier. For example, electrons from inorganic electron donors (nitrite, ferrous iron, electron transport chain) enter the electron transport chain at the cytochrome level. When electrons enter at a redox level greater than NADH, the electron transport chain must operate in reverse to produce this necessary, higher-energy molecule. | 1 | Biochemistry |
A selectable marker is a gene introduced into a cell, especially a bacterium or to cells in culture, that confers a trait suitable for artificial selection. They are a type of reporter gene used in laboratory microbiology, molecular biology, and genetic engineering to indicate the success of a transfection or other procedure meant to introduce foreign DNA into a cell. Selectable markers are often antibiotic resistance genes (An antibiotic resistance marker is a gene that produces a protein that provides cells expressing this protein with resistance to an antibiotic.). Bacteria that have been subjected to a procedure to introduce foreign DNA are grown on a medium containing an antibiotic, and those bacterial colonies that can grow have successfully taken up and expressed the introduced genetic material.
Normally the genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc., are considered useful selectable markers for E. coli. | 1 | Biochemistry |
MicroRNAs (miRNAs) appear to regulate the expression of more than 60% of protein coding genes of the human genome. If an miRNA is abundant it can behave as a "switch", turning some genes on or off. However, altered expression of many miRNAs only leads to a modest 1.5- to 4-fold change in protein expression of their target genes. Individual miRNAs often repress several hundred target genes. Repression usually occurs either through translational silencing of the mRNA or through degradation of the mRNA, via complementary binding, mostly to specific sequences in the 3 untranslated region of the target genes mRNA. The mechanism of translational silencing or degradation of mRNA is implemented through the RNA-induced silencing complex (RISC). | 1 | Biochemistry |
Zinc pest (from German Zinkpest "zinc plague"), also known as zinc rot and zamak rot, is a destructive, intercrystalline corrosion process of zinc alloys containing lead impurities. While impurities of the alloy are the primary cause of the problem, environmental conditions such as high humidity (greater than 65%) may accelerate the process.
It was first discovered to be a problem in 1923, and primarily affects die-cast zinc articles that were manufactured during the 1920s through 1950s. The New Jersey Zinc Company developed zamak alloys in 1929 using 99.99% pure zinc metal to avoid the problem, and articles made after 1960 are usually considered free of the risk of zinc pest since the use of purer materials and more controlled manufacturing conditions make zinc pest degradation unlikely.
Affected objects may show surface irregularities such as small cracks and fractures, blisters or pitting. Over time, the material slowly expands, cracking, buckling and warping in an irreversible process that makes the object exceedingly brittle and prone to fracture, and can eventually shatter the object, destroying it altogether. Due to the expansion process, attached normal material may also be damaged. The occurrence and severity of zinc pest in articles made of susceptible zinc alloys depends both on the concentration of lead impurities in the metal and on the storage conditions of the article in the ensuing decades. Zinc pest is dreaded by collectors of vintage die-cast model trains, toys, or radios, because rare or otherwise valuable items can inescapably be rendered worthless as the process of zinc pest destroys them. Because castings of the same object were usually made from various batches of metal over the production process, some examples of a given toy or model may survive today completely unaffected, while other identical examples may have completely disintegrated. It has also affected carburetors, hubcaps, door handles and automobile trim on cars of the 1920s and 1930s.
Since the 1940s, some model railroad hobbyists have claimed, with varying degrees of success, that a method of "pickling" zinc alloy parts by soaking them in vinegar or oxalic acid solution for several minutes before painting and assembling them could prevent or delay the effects of zinc pest.
Engine parts of older vehicles or airplanes, and military medals made of zinc alloys, may also be affected. In addition, the post-1982 copper-plated zinc Lincoln cents have been known to be affected.
Zinc pest is not related to tin pest, and is also different from a superficial white corrosion oxidation process ("Weissrost") that affects some zinc articles. | 8 | Metallurgy |
The stationary phase comes in the form of a packed syringe-shaped cartridge, a 96 well plate, a 47- or 90-mm flat disk, or a microextraction by packed sorbent (MEPS) device, a SPE method that uses a packed sorbent material in a liquid handling syringe. These can be mounted on its specific type of extraction manifold. The manifold allows multiple samples to be processed by holding several SPE media in place and allowing for an equal number of samples to pass through them simultaneously. In a standard cartridge SPE manifold up to 24 cartridges can be mounted in parallel, while a typical disk SPE manifold can accommodate 6 disks. Most SPE manifolds are equipped with a vacuum port, where vacuum can be applied to speed up the extraction process by pulling the liquid sample through the stationary phase. The analytes are collected in sample tubes inside or below the manifold after they pass through the stationary phase.
Solid phase extraction cartridges and disks can be purchased with several stationary phases, each of which separates analytes depending on different chemical properties. The basis of most stationary phases is silica that has been bonded to a specific functional group. Some of these functional groups include hydrophobic alkyl or aryl chains chains of variable length (for reversed phase), quaternary ammonium or amino groups (for anion exchange), and aliphatic sulfonic acid or carboxyl groups (for cation exchange). | 3 | Analytical Chemistry |
The Frozen Zoo at the San Diego Zoo's Institute for Conservation Research currently stores a collection of 8,400 samples from over 800 species and subspecies. Frozen Zoo at San Diego Zoo Conservation Research has acted as a forebear to similar projects at other zoos in the United States and Europe. However, there are still less than a dozen frozen zoos worldwide.
At the United Arab Emirates Breeding Centre for Endangered Arabian Wildlife (BCEAW) in Sharjah, the embryos stored include the extremely endangered Gordons wildcat (Felis silvestris gordoni) and the Arabian leopard (Panthera pardus nimr) (of which there are only 50 in the wild).
The Audubon Center for Research of Endangered Species, affiliated with the University of New Orleans, is maintaining a frozen zoo. In 2000 the Center implanted a frozen-thawed embryo from the highly endangered African wildcat into the uterus of a domestic house cat, resulting in a healthy male wildcat.
The Frozen Ark is a frozen zoo established in 2004 and jointly managed by the Zoological Society of London, the London Natural History Museum, and the University of Nottingham. This organization operates as a charity with many different departments including the DNA laboratory, consortium, taxon expert groups, and the database. In the DNA laboratory, samples are contained after collection from scientists, and different research projects are conducted there. The consortium acts as a bridge to bring together different, but important, groups from zoos, aquariums, museums, and universities. The taxon expert groups monitor the major phyla and lists like the IUCN Red List. The database is the essential piece as it holds all reports and records needed to perform all of the other functions for the charity. The hope for the future is for zoos and aquariums to be able to collect samples from their threatened and/or endangered species in house to help with conservation efforts. The collection and freezing of these samples allows for the distribution of gametes among populations. Samples can be collected from living hosts and from deceased hosts as well.
The University of Georgia's Regenerative Bioscience Center is building a frozen zoo. RBC Director Steven Stice and animal and dairy science assistant professor Franklin West created the facility with the thought of saving endangered cat species. The scientists have already extracted cells from a Sumatran tiger, which could be used for artificial insemination. Artificial insemination provides a remedy for animals who, due to anatomical or physiological reasons, are unable to reproduce in the natural way. Reproduction of stored genetic material also allows for the fostering of genetic improvements, and the prevention of inbreeding. Modern technology allows for genetic manipulation in animals without keeping them in captivity. However, the success of their restoration into the wild would require the application of new science and a sufficient amount of previously collected material. | 1 | Biochemistry |
In medicine, protein electrophoresis is a method of analysing the proteins mainly in blood serum. Before the widespread use of gel electrophoresis, protein electrophoresis was performed as free-flow electrophoresis (on paper) or as immunoelectrophoresis.
Traditionally, two classes of blood proteins are considered: serum albumin and globulin. They are generally equal in proportion, but albumin as a molecule is much smaller and lightly, negatively-charged, leading to an accumulation of albumin on the electrophoretic gel. A small band before albumin represents transthyretin (also named prealbumin). Some forms of medication or body chemicals can cause their own band, but it usually is small. Abnormal bands (spikes) are seen in monoclonal gammopathy of undetermined significance and multiple myeloma, and are useful in the diagnosis of these conditions.
The globulins are classified by their banding pattern (with their main representatives):
* The alpha (α) band consists of two parts, 1 and 2:
** α - α-antitrypsin, α-acid glycoprotein.
** α - haptoglobin, α-macroglobulin, α-antiplasmin, ceruloplasmin.
* The beta (β) band - transferrin, LDL, complement
* The gamma (γ) band - immunoglobulin (IgA, IgD, IgE, IgG and IgM). Paraproteins (in multiple myeloma) usually appear in this band. | 1 | Biochemistry |
There is no specific antidote to common tear gases. At the first sign of exposure or potential exposure, masks are applied when available. People are removed from the affected area when possible. Immediate removal of contact lenses has also been recommended, as they can retain particles.
Decontamination is by physical or mechanical removal (brushing, washing, rinsing) of solid or liquid agents. Water may transiently exacerbate the pain caused by CS gas and pepper spray but is still effective, although fat-containing oils or soaps may be more effective against pepper spray. Eyes are decontaminated by copious flushing with sterile water or saline or (with OC) open-eye exposure to wind from a fan. Referral to an ophthalmologist is needed if slit-lamp examination shows impaction of solid particles of agent. Blowing the nose to get rid of the chemicals is recommended, as is avoiding rubbing of the eyes. There are reports that water may increase pain from CS gas, but the balance of limited evidence currently suggests water or saline are the best options. Some evidence suggests that Diphoterine, a hypertonic amphoteric salt solution, a first aid product for chemical splashes, may help with ocular burns or chemicals in the eye.
Bathing and washing the body vigorously with soap and water can remove particles that adhere to the skin. Clothes, shoes and accessories that come into contact with vapors must be washed well since all untreated particles can remain active for up to a week. Some advocate using fans or hair dryers to evaporate the spray, but this has not been shown to be better than washing out the eyes and it may spread contamination.
Anticholinergics can work like some antihistamines as they reduce lacrymation and decrease salivation, acting as an antisialagogue, and for overall nose discomfort as they are used to treat allergic reactions in the nose (e.g., itching, runny nose, and sneezing).
Oral analgesics may help relieve eye pain.
Most effects resulting from riot-control agents are transient and do not require treatment beyond decontamination, and most patients do not need observation beyond 4 hours. However, patients should be instructed to return if they develop effects such as blistering or delayed-onset shortness of breath. | 1 | Biochemistry |
Molecular dynamics methods of calculating pK values make it possible to include full flexibility of the titrated molecule.
Molecular dynamics based methods are typically much more computationally expensive, and not necessarily more accurate, ways to predict pK values than approaches based on the Poisson–Boltzmann equation. Limited conformational flexibility can also be realized within a continuum electrostatics approach, e.g., for considering multiple amino acid sidechain rotamers. In addition, current commonly used molecular force fields do not take electronic polarizability into account, which could be an important property in determining protonation energies. | 7 | Physical Chemistry |
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