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Although polyrotaxanes are formed from components, their solubilities are different from the host or guest molecules. For examples, in the cyclodextrin-based polyrotaxanes, due to the hydrophilicity or high polarity of exterior structure of the cyclodextrins, some polyrotaxanes are able to be dissolved in water or other polar solvents though the guest molecules are hydrophobic or nonpolar. These water-soluble can be applied into drug or gene carriers.
There are two main advantages for polyrotaxanes applied to drug/gene delivery: | 6 | Supramolecular Chemistry |
Many physicists simply give up on a microscopic approach, and make informed guesses of the expected phases (perhaps based on NJL model results). For each phase, they then write down an effective theory for the low-energy excitations, in terms of a small number of parameters, and use it to make predictions that could allow those parameters to be fixed by experimental observations. | 7 | Physical Chemistry |
Trans-regulatory elements (TRE) are DNA sequences encoding upstream regulators (ie. trans-acting factors), which may modify or regulate the expression of distant genes. Trans-acting factors interact with cis-regulatory elements to regulate gene expression. TRE mediates expression profiles of a large number of genes via trans-acting factors. While TRE mutations affect gene expression, it is also one of the main driving factors for evolutionary divergence in gene expression. | 1 | Biochemistry |
Cyclic olefin copolymer (COC) is an amorphous polymer made by several polymer manufacturers. COC is a relatively new class of polymers as compared to commodities such as polypropylene and polyethylene. This newer material is used in a wide variety of applications including packaging films, lenses, vials, displays, and medical devices. | 7 | Physical Chemistry |
In chemistry, a pseudorotation is a set of intramolecular movements of attached groups (i.e., ligands) on a highly symmetric molecule, leading to a molecule indistinguishable from the initial one. The International Union of Pure and Applied Chemistry (IUPAC) defines a pseudorotation as a "stereoisomerization resulting in a structure that appears to have been produced by rotation of the entire initial molecule", the result of which is a "product" that is "superposable on the initial one, unless different positions are distinguished by substitution, including isotopic substitution."
Well-known examples are the intramolecular isomerization of trigonal bipyramidal compounds by the Berry pseudorotation mechanism, and the out-of-plane motions of carbon atoms exhibited by cyclopentane, leading to the interconversions it experiences between its many possible conformers (envelope, twist). Note, no angular momentum is generated by this motion. In these and related examples, a small displacement of the atomic positions leads to a loss of symmetry until the symmetric product re-forms (see image example below), where these displacements are typically along low-energy pathways. The Berry mechanism refers to the facile interconversion of axial and equatorial ligand in types of compounds, e.g. D-symmetric (shown). Finally, in a formal sense, the term pseudorotation is intended to refer exclusively to dynamics in symmetrical molecules, though mechanisms of the same type are invoked for lower symmetry molecules as well. | 4 | Stereochemistry |
The Institute of Physical Chemistry of the Polish Academy of Sciences (Polish Instytut Chemii Fizycznej Polskiej Akademii Nauk) is one of numerous institutes belonging to the Polish Academy of Sciences. As its name suggests, the institute's primary research interests are in the field of physical chemistry. The institute is subdivided into departments, including the Department of Soft Condensed Matter and Fluids, the Department of Physical Chemistry of Supramolecular Complexes, the Department of Photochemistry and Spectroscopy and the Department of Quantum Theory of Solids and Molecules, this is also known as the PIPC. | 7 | Physical Chemistry |
It was first developed and utilized by Roy Britten and his colleagues at the Carnegie Institution of Washington in the 1960s. Of particular note, it was through Ct analysis that the redundant (repetitive) nature of eukaryotic genomes was first discovered. However, it wasn't until the breakthrough DNA reassociation kinetics experiments of Britten and his colleagues that it was shown that not all DNA coded for genes. In fact, their experiments demonstrated that the majority of eukaryotic genomic DNA is composed of repetitive, non-coding elements. | 1 | Biochemistry |
After completing his PhD, Philipp Kukura moved to Zürich. There he worked at the Swiss Federal Institute of Technology as a postdoctoral research assistant under the supervision of Professor Vahid Sandoghdar on nano-optics until 2010. He returned to Oxford in 2010 to work initially as an EPSRC Career Acceleration Fellow. In 2011 he was elected to a tutorial fellowship at Exeter College. In 2016 he was promoted to Full Professor of Chemistry.
In 2018 Philipp Kukura founded Refeyn Ltd. together with Justin Benesch, Daniel Cole, and Gavin Young to commercialise mass photometry. | 7 | Physical Chemistry |
Easson and Stedman (1933) advanced a drug-receptor interaction model to account for the differential pharmacodynamic activity between enantiomeric pairs. In this model the more active enantiomer (the eutomer) take part in a minimum of three simultaneous intermolecular interactions with the receptor surface (good fit), Figure. A., where as the less active enantiomer (distomer) interacts at two sites only (bad fit), Figure B. [Refer image for Figure: Easson-Stedman model]. Thus the "fit" of the individual enantiomers to the receptor site differs, as does the energy of interaction. This is a simplistic model but used to explain the biological discrimination between enantiomeric pairs.
In reality the drug-receptor interaction is not that simple, but this view of such complex phenomenon has provided major insights into the mechanism of action of drugs. | 4 | Stereochemistry |
In the 1950s and 1960s, steroidogenic pathways that included cholesterol conversion to progesterone through a complex pathway involving multiple steps were identified, and, among them, a pathway for cortisol synthesis showing specific enzymatic steps that included hydroxylation reactions at position 21 (21-hydroxylation) mediated by cytochrome P450 enzymes. Cytochrome P450 enzymes were then described, and steroid 21-hydroxylation was associated with cytochrome P450.
In the 1980s and 1990s, partial-length bovine Cyp21 cDNA clones were identified as related to human CYP21A2. Researchers discovered mutations in the CYP21A2 gene associated with congenital adrenal hyperplasia (CAH).
From the 1990s onward, specific mutations were correlated with different forms/severity levels of CAH. Genotype/phenotype correlations were investigated for improved diagnostic accuracy. | 1 | Biochemistry |
Dimethylcalcium is obtained by metathesis reaction of calcium bis(trimethylsilyl)amide and methyllithium in diethyl ether:
A well known organocalcium compound is (Cp)calcium(I). Bis(allyl)calcium was described in 2009. It forms in a metathesis reaction of allylpotassium and calcium iodide as a stable non-pyrophoric off-white powder:
The bonding mode is η. This compound is also reported to give access to an η polymeric (CaCHCHCH) compound.
The compound [(thf)Ca{μ-CH-1,3,5-Ph}Ca(thf)] also described in 2009 is an inverse sandwich compound with two calcium atoms at either side of an arene.
Olefins tethered to cyclopentadienyl ligands have been shown to coordinate to calcium(II), strontium(II), and barium(II):
Organocalcium compounds have been investigated as catalysts. | 0 | Organic Chemistry |
Ogston was educated at Eton College and Balliol College, Oxford. Apart from a period as Freedom Research Fellow at the London Hospital, he spent most of his career at Oxford, being appointed Demonstrator (1938) and Reader (1955) in Biochemistry, and Fellow and Tutor in Physical Chemistry at Balliol (1937). In that capacity he had a major influence on other distinguished scientists, such as the Nobel prizewinner Oliver Smithies, who wrote his first paper with him, and Richard Dawkins, who chose to study zoology on his recommendation. In 1959 he took up an appointment as Professor of Physical Biochemistry at the John Curtin School of Medical Research at the Australian National University (ANU), Canberra, where he remained until 1970, when he returned to Oxford as President of Trinity College. On his retirement in 1978, he held visiting fellowships at the Institute for Cancer Research, Philadelphia and the John Curtin School of Medical Research, ANU. Ogston was elected FRS in 1955, and was awarded Lemberg Medal in 1970 and the Davy Medal in 1986. | 4 | Stereochemistry |
The RFU measurements are used, for DNA profiling, in a real-time polymerase chain reaction (PCR). Two common methods for detection of products in real-time PCR are: (1) non-specific fluorescent dyes that intercalate with any double-stranded DNA, and (2) sequence-specific DNA probes consisting of oligonucleotides that are labeled with a fluorescent reporter which permits detection only after hybridization of the probe with its complementary DNA target. Frequently, real-time PCR is combined with reverse transcription to quantify messenger RNA and Non-coding RNA in cells or tissues. | 1 | Biochemistry |
Levonorgestrel stimulates the proliferation of MCF-7 breast cancer cells in vitro, an action that is independent of the classical PRs and is instead mediated via the progesterone receptor membrane component-1 (PGRMC1). Certain other progestins act similarly in this assay, whereas progesterone acts neutrally. It is unclear if these findings may explain the different risks of breast cancer observed with progesterone and progestins in clinical studies. | 4 | Stereochemistry |
Unruh demonstrated theoretically that the notion of vacuum depends on the path of the observer through spacetime. From the viewpoint of the accelerating observer, the vacuum of the inertial observer will look like a state containing many particles in thermal equilibrium—a warm gas.
The Unruh effect would only appear to an accelerating observer. And although the Unruh effect would initially be perceived as counter-intuitive, it makes sense if the word vacuum is interpreted in the following specific way. In quantum field theory, the concept of "vacuum" is not the same as "empty space": Space is filled with the quantized fields that make up the universe. Vacuum is simply the lowest possible energy state of these fields.
The energy states of any quantized field are defined by the Hamiltonian, based on local conditions, including the time coordinate. According to special relativity, two observers moving relative to each other must use different time coordinates. If those observers are accelerating, there may be no shared coordinate system. Hence, the observers will see different quantum states and thus different vacua.
In some cases, the vacuum of one observer is not even in the space of quantum states of the other. In technical terms, this comes about because the two vacua lead to unitarily inequivalent representations of the quantum field canonical commutation relations. This is because two mutually accelerating observers may not be able to find a globally defined coordinate transformation relating their coordinate choices.
An accelerating observer will perceive an apparent event horizon forming (see Rindler spacetime). The existence of Unruh radiation could be linked to this apparent event horizon, putting it in the same conceptual framework as Hawking radiation. On the other hand, the theory of the Unruh effect explains that the definition of what constitutes a "particle" depends on the state of motion of the observer.
The free field needs to be decomposed into positive and negative frequency components before defining the creation and annihilation operators. This can only be done in spacetimes with a timelike Killing vector field. This decomposition happens to be different in Cartesian and Rindler coordinates (although the two are related by a Bogoliubov transformation). This explains why the "particle numbers", which are defined in terms of the creation and annihilation operators, are different in both coordinates.
The Rindler spacetime has a horizon, and locally any non-extremal black hole horizon is Rindler. So the Rindler spacetime gives the local properties of black holes and cosmological horizons. It is possible to rearrange the metric restricted to these regions to obtain the Rindler metric. The Unruh effect would then be the near-horizon form of Hawking radiation.
The Unruh effect is also expected to be present in de Sitter space.
It is worth stressing that the Unruh effect only says that, according to uniformly-accelerated observers, the vacuum state is a thermal state specified by its temperature, and one should resist reading too much into the thermal state or bath. Different thermal states or baths at the same temperature need not be equal, for they depend on the Hamiltonian describing the system. In particular, the thermal bath seen by accelerated observers in the vacuum state of a quantum field is not the same as a thermal state of the same field at the same temperature according to inertial observers. Furthermore, uniformly accelerated observers, static with respect to each other, can have different proper accelerations (depending on their separation), which is a direct consequence of relativistic red-shift effects. This makes the Unruh temperature spatially inhomogeneous across the uniformly accelerated frame. | 7 | Physical Chemistry |
The law itself can be stated as follows:
Boyle's law is a gas law, stating that the pressure and volume of a gas have an inverse relationship. If volume increases, then pressure decreases and vice versa, when the temperature is held constant.
Therefore, when the volume is halved, the pressure is doubled; and if the volume is doubled, the pressure is halved. | 7 | Physical Chemistry |
Efforts to understand how proteins are encoded began after DNA's structure was discovered in 1953. The key discoverers, English biophysicist Francis Crick and American biologist James Watson, working together at the Cavendish Laboratory of the University of Cambridge, hypothesied that information flows from DNA and that there is a link between DNA and proteins. Soviet-American physicist George Gamow was the first to give a workable scheme for protein synthesis from DNA. He postulated that sets of three bases (triplets) must be employed to encode the 20 standard amino acids used by living cells to build proteins, which would allow a maximum of amino acids. He named this DNA–protein interaction (the original genetic code) as the "diamond code".
In 1954, Gamow created an informal scientific organisation the RNA Tie Club, as suggested by Watson, for scientists of different persuasions who were interested in how proteins were synthesised from genes. However, the club could have only 20 permanent members to represent each of the 20 amino acids; and four additional honorary members to represent the four nucleotides of DNA.
The first scientific contribution of the club, later recorded as "one of the most important unpublished articles in the history of science" and "the most famous unpublished paper in the annals of molecular biology", was made by Crick. Crick presented a type-written paper titled "On Degenerate Templates and the Adaptor Hypothesis: A Note for the RNA Tie Club" to the members of the club in January 1955, which "totally changed the way we thought about protein synthesis", as Watson recalled. The hypothesis states that the triplet code was not passed on to amino acids as Gamow thought, but carried by a different molecule, an adaptor, that interacts with amino acids. The adaptor was later identified as tRNA. | 1 | Biochemistry |
Iron is used a great deal in biological systems, a fact that is well known due to its role in Hemoglobin. For it, there are many small molecule sensors including:
*Pryrene-TEMPO, in which the binding of iron to TEMPO quenches the fluorescence of pyrene when no Fe(II) is bound. Upon binding however, TEMPO is reduced and pyrene regains fluorescence. This probe is limited in that an analogous response can be generated by unwanted free radicals, and that it can only by used in acidic solution.
*DansSQ, in which Fe(II) binding increases fluorescence at 460 nm. It consists of a Dansyl group bound to styrylquinoline and operates by the disruption of intra-molecular charge transfer upon the binding of Fe(II). It is limited in that it is only soluble in acetonitrile in 10% HO. | 5 | Photochemistry |
Water vapor and dry air density calculations at 0 °C:
* The molar mass of water is , as calculated from the sum of the atomic masses of its constituent atoms.
* The average molar mass of air (approx. 78% nitrogen, N; 21% oxygen, O; 1% other gases) is at standard temperature and pressure (STP).
* Obeying Avogadro's Law and the ideal gas law, moist air will have a lower density than dry air. At max. saturation (i. e. rel. humidity = 100% at 0 °C) the density will go down to 28.51 g/mol.
* STP conditions imply a temperature of 0 °C, at which the ability of water to become vapor is very restricted. Its concentration in air is very low at 0 °C. The red line on the chart to the right is the maximum concentration of water vapor expected for a given temperature. The water vapor concentration increases significantly as the temperature rises, approaching 100% (steam, pure water vapor) at 100 °C. However the difference in densities between air and water vapor would still exist (0.598 vs. 1.27 g/L). | 2 | Environmental Chemistry |
Ultraviolet (UV) light is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs, Cherenkov radiation, and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights.
The photons of ultraviolet have greater energy than those of visible light, from about 3.1 to 12 electron volts, around the minimum energy required to ionize atoms. Although long-wavelength ultraviolet is not considered an ionizing radiation because its photons lack sufficient energy, it can induce chemical reactions and cause many substances to glow or fluoresce. Many practical applications, including chemical and biological effects, are derived from the way that UV radiation can interact with organic molecules. These interactions can involve absorption or adjusting energy states in molecules, but do not necessarily involve heating. Short-wave ultraviolet light is ionizing radiation. Consequently, short-wave UV damages DNA and sterilizes surfaces with which it comes into contact.
For humans, suntan and sunburn are familiar effects of exposure of the skin to UV light, along with an increased risk of skin cancer. The amount of UV light produced by the Sun means that the Earth would not be able to sustain life on dry land if most of that light were not filtered out by the atmosphere. More energetic, shorter-wavelength "extreme" UV below 121 nm ionizes air so strongly that it is absorbed before it reaches the ground. However, ultraviolet light (specifically, UVB) is also responsible for the formation of vitamin D in most land vertebrates, including humans. The UV spectrum, thus, has effects both beneficial and detrimental to life.
The lower wavelength limit of the visible spectrum is conventionally taken as 400 nm, so ultraviolet rays are not visible to humans, although people can sometimes perceive light at shorter wavelengths than this. Insects, birds, and some mammals can see near-UV (NUV), i.e., slightly shorter wavelengths than what humans can see. | 5 | Photochemistry |
Walsh diagrams in conjunction with molecular orbital theory can also be used as a tool to predict reactivity. By generating a Walsh Diagram and then determining the HOMO/LUMO of that molecule, it can be determined how the molecule is likely to react. In the following example, the Lewis acidity of AH molecules such as BH and CH is predicted.
Six electron AH molecules should have a planar conformation. It can be seen that the HOMO, 1e’, of planar AH is destabilized upon bending of the A-H bonds to form a pyramid shape, due to disruption of bonding. The LUMO, which is concentrated on one atomic center, is a good electron acceptor and explains the Lewis acid character of BH and CH.
Walsh correlation diagrams can also be used to predict relative molecular orbital energy levels. The distortion of the hydrogen atoms from the planar CH to the tetrahedral CH-Nu causes a stabilization of the C-Nu bonding orbital, σ. | 7 | Physical Chemistry |
For faster reactions, the time required to mix the reactants and bring them to a specified temperature may be comparable or longer than the half-life of the reaction. Special methods to start fast reactions without slow mixing step include
* Stopped flow methods, which can reduce the mixing time to the order of a millisecond The stopped flow methods have limitation, for example, we need to consider the time it takes to mix gases or solutions and are not suitable if the half-life is less than about a hundredth of a second.
* Chemical relaxation methods such as temperature jump and pressure jump, in which a pre-mixed system initially at equilibrium is perturbed by rapid heating or depressurization so that it is no longer at equilibrium, and the relaxation back to equilibrium is observed. For example, this method has been used to study the neutralization HO + OH with a half-life of 1 μs or less under ordinary conditions.
* Flash photolysis, in which a laser pulse produces highly excited species such as free radicals, whose reactions are then studied. | 7 | Physical Chemistry |
PKA is also commonly known as cAMP-dependent protein kinase, because it has traditionally been thought to be activated through release of the catalytic subunits when levels of the second messenger called cyclic adenosine monophosphate, or cAMP, rise in response to a variety of signals. However, recent studies evaluating the intact holoenzyme complexes, including regulatory AKAP-bound signalling complexes, have suggested that the local sub cellular activation of the catalytic activity of PKA might proceed without physical separation of the regulatory and catalytic components, especially at physiological concentrations of cAMP. In contrast, experimentally induced supra physiological concentrations of cAMP, meaning higher than normally observed in cells, are able to cause separation of the holoenzymes, and release of the catalytic subunits.
Extracellular hormones, such as glucagon and epinephrine, begin an intracellular signalling cascade that triggers protein kinase A activation by first binding to a G protein–coupled receptor (GPCR) on the target cell. When a GPCR is activated by its extracellular ligand, a conformational change is induced in the receptor that is transmitted to an attached intracellular heterotrimeric G protein complex by protein domain dynamics. The Gs alpha subunit of the stimulated G protein complex exchanges GDP for GTP in a reaction catalyzed by the GPCR and is released from the complex. The activated Gs alpha subunit binds to and activates an enzyme called adenylyl cyclase, which, in turn, catalyzes the conversion of ATP into cAMP, directly increasing the cAMP level. Four cAMP molecules are able to bind to the two regulatory subunits. This is done by two cAMP molecules binding to each of the two cAMP binding sites (CNB-B and CNB-A) which induces a conformational change in the regulatory subunits of PKA, causing the subunits to detach and unleash the two, now activated, catalytic subunits.
Once released from inhibitory regulatory subunit, the catalytic subunits can go on to phosphorylate a number of other proteins in the minimal substrate context Arg-Arg-X-Ser/Thr., although they are still subject to other layers of regulation, including modulation by the heat stable pseudosubstrate inhibitor of PKA, termed PKI.
Below is a list of the steps involved in PKA activation:
# Cytosolic cAMP increases
# Two cAMP molecules bind to each PKA regulatory subunit
# The regulatory subunits move out of the active sites of the catalytic subunits and the R2C2 complex dissociates
# The free catalytic subunits interact with proteins to phosphorylate Ser or Thr residues. | 1 | Biochemistry |
* [https://sosradon.org/devices National radon program services]. Kansas State University. Accessed 17 October 2017. | 2 | Environmental Chemistry |
The unfavourable reduction of Fd from a less reducing electron donor can be coupled simultaneously with the favourable reduction of an oxidising agent through an electron bifurcation reaction. An example of the electron bifurcation reaction is the generation of for nitrogen fixation in certain aerobic diazotrophs. Typically in oxidative phosphorylation the transfer of electrons from NADH to Ubiquinone(Q) is coupled to charging the proton motive force. In Azotobacter the energy released by transferring one electron from NADH to Q is used to simultaneously boost the transfer of one electron from NADH to Fd. | 5 | Photochemistry |
The Hofmann rearrangement is a decarbonylation reaction whereby an amide is converted to an amine by way of an isocyanate intermediate. It is usually carried out under strongly basic conditions.
The reaction can also be carried out under mildly acidic conditions by way of the same intermediate using a hypervalent iodine compound in aqueous solution. An example published in Organic Syntheses is the conversion of cyclobutanecarboxamide, easily synthesized from cyclobutylcarboxylic acid, to cyclobutylamine. The primary amine is initially present as its trifluoroacetate salt, which can be converted to the hydrochloride salt to facilitate product purification. | 0 | Organic Chemistry |
For a thermodynamic process, the precise physical properties of the walls and surroundings of the system are important, because they determine the possible processes.
An open system has one or several walls that allow transfer of matter. To account for the internal energy of the open system, this requires energy transfer terms in addition to those for heat and work. It also leads to the idea of the chemical potential.
A wall selectively permeable only to a pure substance can put the system in diffusive contact with a reservoir of that pure substance in the surroundings. Then a process is possible in which that pure substance is transferred between system and surroundings. Also, across that wall a contact equilibrium with respect to that substance is possible. By suitable thermodynamic operations, the pure substance reservoir can be dealt with as a closed system. Its internal energy and its entropy can be determined as functions of its temperature, pressure, and mole number.
A thermodynamic operation can render impermeable to matter all system walls other than the contact equilibrium wall for that substance. This allows the definition of an intensive state variable, with respect to a reference state of the surroundings, for that substance. The intensive variable is called the chemical potential; for component substance it is usually denoted . The corresponding extensive variable can be the number of moles of the component substance in the system.
For a contact equilibrium across a wall permeable to a substance, the chemical potentials of the substance must be same on either side of the wall. This is part of the nature of thermodynamic equilibrium, and may be regarded as related to the zeroth law of thermodynamics. | 7 | Physical Chemistry |
"Clinker" is from Dutch, and was originally used in English to describe clinker bricks. The term was later applied to hard residue, due to its similar appearance. | 8 | Metallurgy |
NANOHISPA and NIMS-MANA were both ranked first, both making about 54 turns and covering 678 nm and 1054 nm, respectively. The first demonstrated a change of lane for overpassing while the latter crossed a trench and go back. StrasNanocar ranked third covering 476 nm and performing 28 turns. | 6 | Supramolecular Chemistry |
Models predict a seasonal nitrogen cycle on Pluto and observations by New Horizons appear to support this. | 9 | Geochemistry |
Morpholine oleate is used in glazing wax which covers fruit. NMOR can be generated by the nitration of morpholine, causing its presence in waxed fruits.Health Canada, the Canadian governmental department of public health, has stated in 2002 that this does not pose a risk to human health.
Consumption of nitrate-rich diets is correlated with levels of salivary and urinary NMOR. The presence of NMOR can also be observed in gastric juices. | 0 | Organic Chemistry |
Theoretically, IVF could be performed by collecting the contents from the fallopian tubes or uterus after natural ovulation, mixing it with sperm, and reinserting the fertilised ova into the uterus. However, without additional techniques, the chances of pregnancy would be extremely small. The additional techniques that are routinely used in IVF include ovarian hyperstimulation to generate multiple eggs, ultrasound-guided transvaginal oocyte retrieval directly from the ovaries, co-incubation of eggs and sperm, as well as culture and selection of resultant embryos before embryo transfer into a uterus. | 1 | Biochemistry |
A typical amount of 32 ng of cfDNA was utilized for library preparation. DNA input was adjusted to mitigate the effects of high molecular-weight DNA contamination. The library preparation process encompassed end repair, A-tailing, and adapter ligation, which also incorporated molecular barcodes into each read. These procedures were conducted according to ligation based library preparation standardized protocols, with overnight ligation performed at 4 °C. Following this, shotgun cfDNA libraries underwent hybrid capture targeting specific genomic regions, as detailed below. | 1 | Biochemistry |
The cDNA molecules generated by RACE can be sequenced using high-throughput sequencing technologies (also called, RACE-seq). High-throughput sequencing characterization of RACE fragments is highly time-efficient, more sensitive, less costly and technically feasible compared to traditional characterization of RACE fragments with molecular cloning followed by Sanger sequencing of a few clones. | 1 | Biochemistry |
Measured area depends on instrument design. The minimum analysis area ranges from 10 to 200 micrometres. Largest size for a monochromatic beam of X-rays is 1–5 mm. Non-monochromatic beams are 10–50 mm in diameter. Spectroscopic image resolution levels of 200 nm or below has been achieved on latest imaging XPS instruments using synchrotron radiation as X-ray source. | 7 | Physical Chemistry |
In chemistry, a non-covalent interaction differs from a covalent bond in that it does not involve the sharing of electrons, but rather involves more dispersed variations of electromagnetic interactions between molecules or within a molecule. The chemical energy released in the formation of non-covalent interactions is typically on the order of 1–5 kcal/mol (1000–5000 calories per 6.02 molecules). Non-covalent interactions can be classified into different categories, such as electrostatic, π-effects, van der Waals forces, and hydrophobic effects.
Non-covalent interactions are critical in maintaining the three-dimensional structure of large molecules, such as proteins and nucleic acids. They are also involved in many biological processes in which large molecules bind specifically but transiently to one another (see the properties section of the DNA page). These interactions also heavily influence drug design, crystallinity and design of materials, particularly for self-assembly, and, in general, the synthesis of many organic molecules.
The non-covalent interactions may occur between different parts of the same molecule (e.g. during protein folding) or between different molecules and therefore are discussed also as intermolecular forces. | 6 | Supramolecular Chemistry |
When using the entropy change of a process to assess spontaneity, it is important to carefully consider the definition of the system and surroundings. The second law of thermodynamics states that a process involving an isolated system will be spontaneous if the entropy of the system increases over time. For open or closed systems, however, the statement must be modified to say that the total entropy of the combined system and surroundings must increase, or,
This criterion can then be used to explain how it is possible for the entropy of an open or closed system to decrease during a spontaneous process. A decrease in system entropy can only occur spontaneously if the entropy change of the surroundings is both positive in sign and has a larger magnitude than the entropy change of the system:
and
In many processes, the increase in entropy of the surroundings is accomplished via heat transfer from the system to the surroundings (i.e. an exothermic process). | 7 | Physical Chemistry |
Polychlorinated biphenyls (PCBs) are highly carcinogenic chemical compounds, formerly used in industrial and consumer products, whose production was banned in the United States by the Toxic Substances Control Act in 1976 and internationally by the Stockholm Convention on Persistent Organic Pollutants in 2001.
PCBs are organochlorine compounds with the formula CHCl; they were once widely used in the manufacture of carbonless copy paper, as heat transfer fluids, and as dielectric and coolant fluids for electrical equipment.
Because of their longevity, PCBs are still widely in use, even though their manufacture has declined drastically since the 1960s, when a host of problems were identified. With the discovery of PCBs' environmental toxicity, and classification as persistent organic pollutants, their production was banned for most uses by United States federal law on January 1, 1978, under Title 15 U.S.Code 2605(e) Polychlorinated biphenyls, in subsection (2)(A) established that after January 1, 1978, "no person may manufacture, process or distribute in commerce or use any PCB in any manner other than in a totally enclosed manner (...)" EPA may also regulate PCB disposal.
The International Agency for Research on Cancer (IARC) rendered PCBs as definite carcinogens in humans. According to the U.S. Environmental Protection Agency (EPA), PCBs cause cancer in animals and are probable human carcinogens. Many rivers and buildings, including schools, parks, and other sites, are contaminated with PCBs and there has been contamination of food supplies with the substances. Moreover, because of their use as a coolant in electric transformers, PCBs still persist in built environments.
Some PCBs share a structural similarity and toxic mode of action with dioxins. Other toxic effects such as endocrine disruption (notably blocking of thyroid system functioning) and neurotoxicity are known. The bromine analogues of PCBs are polybrominated biphenyls (PBBs), which have analogous applications and environmental concerns.
An estimated 1.2 million tons have been produced globally. Though the EPA enforced the federal ban as of 1978, PCBs continued to create health problems in later years through their continued presence in soil and sediment, and from products which were made before 1979. In 1988, Japanese scientists Tanabe et al. estimated 370,000 tons were in the environment globally, and 780,000 tons were present in products, landfills, and dumps or kept in storage. | 2 | Environmental Chemistry |
PSII is extremely complex, a highly organized transmembrane structure that contains a water splitting complex, chlorophylls and carotenoid pigments, a reaction center (P680), pheophytin (a pigment similar to chlorophyll), and two quinones. It uses the energy of sunlight to transfer electrons from water to a mobile electron carrier in the membrane called plastoquinone:
Plastoquinol, in turn, transfers electrons to cyt bf, which feeds them into PSI. | 5 | Photochemistry |
In the late 1840s, the German chemist developed a modification of the puddling process to produce not iron but steel at the Haspe Iron Works in Hagen; it was subsequently commercialized in Germany, France and the UK in the 1850s, and puddled steel was the main raw material for Krupp cast steel even in the 1870s. Before the development of the basic refractory lining (with magnesium oxide, MgO) and the wide-scale adoption of the Gilchrist–Thomas process ca. 1880 it complemented acidic Bessemer converters (with a refractory material made of ) and open hearths because unlike them, the puddling furnace could utilize phosphorous ores abundant in Continental Europe. | 8 | Metallurgy |
The drug should be used with caution in those with liver or kidney failure, due to metabolism in the liver (to the active molecule desmetramadol) and elimination by the kidneys. | 4 | Stereochemistry |
To a first approximation, an example of radiative exchange equilibrium is in the exchange of non-window wavelength thermal radiation between the land-and-sea surface and the lowest atmosphere, when there is a clear sky. As a first approximation (W. C. Swinbank 1963, G. W. Paltridge and C. M. R. Platt 1976, pages 139–140), in the non-window wavenumbers, there is zero net exchange between the surface and the atmosphere, while, in the window wavenumbers, there is simply direct radiation from the land-sea surface to space. A like situation occurs between adjacent layers in the turbulently mixed boundary layer of the lower troposphere, expressed in the so-called "cooling to space approximation", first noted by C. D. Rodgers and C. D. Walshaw (1966). | 7 | Physical Chemistry |
The Holton Taxol total synthesis, published by Robert A. Holton and his group at Florida State University in 1994, was the first total synthesis of Taxol (generic name: paclitaxel).
The Holton Taxol total synthesis is a good example of a linear synthesis. The synthesis starts from patchoulene oxide, a commercially available natural compound .
This epoxide can be obtained in two steps from the terpene patchoulol and also from borneol. The reaction sequence is also enantioselective, synthesizing (+)-Taxol from (−)-patchoulene oxide or (−)-Taxol from (−)-borneol with a reported specific rotation of +- 47° (c=0.19 / MeOH). The Holton sequence to Taxol is relatively short compared to that of the other groups (46 linear steps from patchoulene oxide). One of the reasons is that patchoulene oxide already contains 15 of the 20 carbon atoms required for the Taxol ABCD ring framework.
Other raw materials required for this synthesis include 4-pentenal, m-chloroperoxybenzoic acid, methyl magnesium bromide and phosgene. Two key chemical transformations in this sequence are a Chan rearrangement and a sulfonyloxaziridine enolate oxidation. | 0 | Organic Chemistry |
Applied Organometallic Chemistry is a monthly peer-reviewed scientific journal published since 1987 by John Wiley & Sons.
The editor-in-chief is Cornelis J. Elsevier (University of Amsterdam). | 0 | Organic Chemistry |
A specialized form of cell signaling
*BLOC1S1
*BLOC1S2NM_173809
*BLOC1S3NM_212550
*BLOC1S4NM_018366
*BLOC1S6NM_012388
*AP1G1 NM_001128
*AP1M1 NM_032493
*AP2A1 NM_014203
*AP2A2 NM_012305
*AP2M1
*AP2S1 NM_004069
*AP3B1 NM_003664
*AP3D1 NM_003938
*AP3M1 NM_012095
*AP3S1 NM_001284
*AP3S2 NM_005829
*AP4B1 NM_006594
*AP5M1 NM_018229
*ANXA6 Annexin 6
*ANXA7 Annexin 7
*AP1B1 Coated vesicles
*CLTA Clathrin A (vesicles)
*CLTB Clathrin B (vesicles)
*CLTC | 1 | Biochemistry |
A FMN-binding fluorescent protein (FbFP), also known as a LOV-based fluorescent protein, is a small, oxygen-independent fluorescent protein that binds flavin mononucleotide (FMN) as a chromophore.
They were developed from blue-light receptors (so called LOV-domains) found in plants and various bacteria. They complement the GFP-derivatives and –homologues and are particularly characterized by their independence of molecular oxygen and their small size. FbFPs absorb blue light and emit light in the cyan-green spectral range. | 1 | Biochemistry |
In the analysis of the molecular formula of organic molecules, the degree of unsaturation (DU) (also known as the index of hydrogen deficiency (IHD), double bond equivalents (DBE), or unsaturation index) is a calculation that determines the total number of rings and π bonds. A formula is used in organic chemistry to help draw chemical structures. It does not give any information about those components individually—the specific number of rings, or of double bonds (one π bond each), or of triple bonds (two π bonds each). The final structure is verified with use of NMR, mass spectrometry and IR spectroscopy, as well as qualitative inspection. It is based on comparing the actual molecular formula to what would be a possible formula if the structure were saturated—having no rings and containing only σ bonds—with all atoms having their standard valence. | 0 | Organic Chemistry |
Glyceraldehyde 3-phosphate occurs as a reactant in the biosynthesis pathway of thiamine (Vitamin B), another substance that cannot be produced by the human body. | 5 | Photochemistry |
Two ways the release of volatile organic compounds (VOCs) may benefit plants are the deterrence of herbivores and the attraction of natural enemies. Synthetic products could replicate the distinct VOC profiles released by different plants; these products could be applied to plants suffering from pests that are targeted by the attracted natural enemy. This could cause natural enemies to enter crops that are occupied by pest populations that would otherwise likely remain undetected by the natural enemies.
The four elements that must be considered before manipulating VOCs are as follows: The VOCs must effectively aid the natural enemy in finding the prey; the pest must have natural enemies present; the fitness cost of potentially attracting more herbivores must be exceeded by attracting natural enemies; and the natural enemies must not be negatively affected by direct plant defenses that may be present. | 1 | Biochemistry |
The dissociation constant of water is denoted K:
The concentration of water, [HO], is omitted by convention, which means that the value of K differs from the value of K that would be computed using that concentration.
The value of K varies with temperature, as shown in the table below. This variation must be taken into account when making precise measurements of quantities such as pH. | 7 | Physical Chemistry |
Using a glia-conditioned medium to treat glia-free purified rat retinal ganglion microcultures has been shown to significantly increase the number of autapses per neuron compared to a control. This suggests that glia-derived soluble, proteinase K-sensitive factors induce autapse formation in rat retinal ganglion cells. | 1 | Biochemistry |
The diphosphine ligands have received considerably more attention than the monophosphines and, perhaps as a consequence, have a much longer list of achievement. This class includes the first ligand to achieve high selectivity (DIOP), the first ligand to be used in industrial asymmetric synthesis (DIPAMP) and what is likely the best known chiral ligand (BINAP). Chiral diphosphine ligands are now ubiquitous in asymmetric hydrogenation.
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The pure rotation spectrum of water vapor extends into the microwave region.
Liquid water has a broad absorption spectrum in the microwave region, which has been explained in terms of changes in the hydrogen bond network giving rise to a broad, featureless, microwave spectrum. The absorption (equivalent to dielectric loss) is used in microwave ovens to heat food that contains water molecules. A frequency of 2.45 GHz, wavelength 122 mm, is commonly used.
Radiocommunication at GHz frequencies is very difficult in fresh waters and even more so in salt waters. | 7 | Physical Chemistry |
Diphenylamine is used as a pre- or postharvest scald inhibitor for apples applied as an indoor drench treatment. Its anti-scald activity is the result of its antioxidant properties, which protect the apple skin from the oxidation products of α-farnesene during storage. Apple scald is physical injury that manifests in brown spots after fruit is removed from cold storage. | 3 | Analytical Chemistry |
One important consideration deriving from Kirkendall's work is the presence of pores formed during diffusion. These voids act as sinks for vacancies, and when enough accumulate they can become substantial and expand in an attempt to restore equilibrium. Porosity occurs due to the difference in diffusion rate of the two species.
Pores in metals have ramifications for mechanical, thermal, and electrical properties, and thus control over their formation is often desired. The equation
where is the distance moved by a marker, is a coefficient determined by intrinsic diffusivities of the materials, and is a concentration difference between components, has proven to be an effective model for mitigating Kirkendall porosity. Controlling annealing temperature is another method of reducing or eliminating porosity. Kirkendall porosity typically occurs at a set temperature in a system, so annealing can be performed at lower temperatures for longer times to avoid formation of pores. | 8 | Metallurgy |
Phycocyanobilin is a blue phycobilin, i.e., a tetrapyrrole chromophore found in cyanobacteria and in the chloroplasts of red algae, glaucophytes, and some cryptomonads. Phycocyanobilin is present only in the phycobiliproteins allophycocyanin and phycocyanin, of which it is the terminal acceptor of energy. It is covalently linked to these phycobiliproteins by a thioether bond.
Phycocyanobilin (PCB), has the ability to bind to human serum albumin (HSA), protein found mainly in the blood of humans. This PCB-HCA complex benefits the structure of HSA, increasing the thermal stability of HSA, as well as increasing its ability to prevent against proteolytic activity of other proteins. | 1 | Biochemistry |
Succinyl CoA synthetase catalyzes the following reversible reaction:
:Succinyl CoA + Pi + NDP ↔ Succinate + CoA + NTP
where Pi denotes inorganic phosphate, NDP denotes nucleotide diphosphate (either GDP or ADP), and NTP denotes nucleotide triphosphate (either GTP or ATP). As mentioned, the enzyme facilitates coupling of the conversion of succinyl CoA to succinate with the formation of NTP from NDP and Pi. The reaction has a biochemical standard state free energy change of -3.4 kJ/mol. The reaction takes place by a three-step mechanism which is depicted in the image below. The first step involves displacement of CoA from succinyl CoA by a nucleophilic inorganic phosphate molecule to form succinyl phosphate. The enzyme then utilizes a histidine residue to remove the phosphate group from succinyl phosphate and generate succinate. Finally, the phosphorylated histidine transfers the phosphate group to a nucleoside diphosphate, which generates the high-energy carrying nucleoside triphosphate. | 1 | Biochemistry |
A desmut solution can be applied to the surface of aluminium to remove contaminates. Nitric acid is typically used to remove smut (residue), but is being replaced because of environmental concerns. | 8 | Metallurgy |
The iron catalyst is obtained from finely ground iron powder, which is usually obtained by reduction of high-purity magnetite (FeO). The pulverized iron is oxidized to give magnetite or wüstite (FeO, ferrous oxide) particles of a specific size. The magnetite (or wüstite) particles are then partially reduced, removing some of the oxygen. The resulting catalyst particles consist of a core of magnetite, encased in a shell of wüstite, which in turn is surrounded by an outer shell of metallic iron. The catalyst maintains most of its bulk volume during the reduction, resulting in a highly porous high-surface-area material, which enhances its catalytic effectiveness. Minor components include calcium and aluminium oxides, which support the iron catalyst and help it maintain its surface area. These oxides of Ca, Al, K, and Si are unreactive to reduction by hydrogen.
The production of the catalyst requires a particular melting process in which used raw materials must be free of catalyst poisons and the promoter aggregates must be evenly distributed in the magnetite melt. Rapid cooling of the magnetite, which has an initial temperature of about 3500 °C, produces the desired precursor. Unfortunately, the rapid cooling ultimately forms a catalyst of reduced abrasion resistance. Despite this disadvantage, the method of rapid cooling is often employed.
The reduction of the precursor magnetite to α-iron is carried out directly in the production plant with synthesis gas. The reduction of the magnetite proceeds via the formation of wüstite (FeO) so that particles with a core of magnetite become surrounded by a shell of wüstite. The further reduction of magnetite and wüstite leads to the formation of α-iron, which forms together with the promoters the outer shell. The involved processes are complex and depend on the reduction temperature: At lower temperatures, wüstite disproportionates into an iron phase and a magnetite phase; at higher temperatures, the reduction of the wüstite and magnetite to iron dominates.
The α-iron forms primary crystallites with a diameter of about 30 nanometers. These crystallites form a bimodal pore system with pore diameters of about 10 nanometers (produced by the reduction of the magnetite phase) and of 25 to 50 nanometers (produced by the reduction of the wüstite phase). With the exception of cobalt oxide, the promoters are not reduced.
During the reduction of the iron oxide with synthesis gas, water vapor is formed. This water vapor must be considered for high catalyst quality as contact with the finely divided iron would lead to premature aging of the catalyst through recrystallization, especially in conjunction with high temperatures. The vapor pressure of the water in the gas mixture produced during catalyst formation is thus kept as low as possible, target values are below 3 gm. For this reason, the reduction is carried out at high gas exchange, low pressure, and low temperatures. The exothermic nature of the ammonia formation ensures a gradual increase in temperature.
The reduction of fresh, fully oxidized catalyst or precursor to full production capacity takes four to ten days. The wüstite phase is reduced faster and at lower temperatures than the magnetite phase (FeO). After detailed kinetic, microscopic, and X-ray spectroscopic investigations it was shown that wüstite reacts first to metallic iron. This leads to a gradient of iron(II) ions, whereby these diffuse from the magnetite through the wüstite to the particle surface and precipitate there as iron nuclei.
Pre-reduced, stabilized catalysts occupy a significant market share. They are delivered showing the fully developed pore structure, but have been oxidized again on the surface after manufacture and are therefore no longer pyrophoric. The reactivation of such pre-reduced catalysts requires only 30 to 40 hours instead of several days. In addition to the short start-up time, they have other advantages such as higher water resistance and lower weight. | 7 | Physical Chemistry |
The nucleotide sequences of interest are preserved as inserts to a plasmid or the genome of a bacteriophage that has been used to infect bacterial cells.
Vectors are propagated most commonly in bacterial cells, but if using a YAC (Yeast Artificial Chromosome) then yeast cells may be used. Vectors could also be propagated in viruses, but this can be time-consuming and tedious. However, the high transfection efficiency achieved by using viruses (often phages) makes them useful for packaging the vector (with the ligated insert) and then introducing them into the bacterial (or yeast) cell.
Additionally, for cDNA libraries, a system using the Lambda Zap II phage, ExAssist, and 2 E. coli species has been developed. A Cre-Lox system using loxP sites and the in vivo expression of the recombinase enzyme can also be used instead. These are examples of in vivo excision systems. In vitro excision involves subcloning often using traditional restriction enzymes and cloning strategies. In vitro excision can be more time-consuming and may require more "hands-on" work than in vivo excision systems. In either case, the systems allow the movement of the vector from the phage into a live cell, where the vector can replicate and propagate until the library is to be used. | 1 | Biochemistry |
Dimitra Markovitsi is a Greek-French photochemist. She is currently an Emeritus Research Director at the French National Center for Scientific Research (CNRS). She pioneered studies on the electronically excited states of liquid crystals and made significant advances to the understanding of processes triggered in DNA upon absorption of UV radiation. The two facets of her work have been the subject of a recent Marie Skodowska Curie European training network entitled "Light DyNAmics - DNA as a training platform for photodynamic processes in soft materials." | 5 | Photochemistry |
Fancy and Kodadek's invention of PICUP in 1999 was the first time proteins cross-linking was able to be performed in such a short period of time (1 second) and without modifying the structure of the proteins in question. Additionally, PICUP was able to be performed at physiological pH of 7.4, which opened doors for further application of protein cross-linking such as studying the biochemical mechanisms that proteins participate in the human body. In addition, irradiation by visible light in PICUP is useful because many biomolecules that participate in metabolic pathways to be analyzed do no absorb light with wavelengths below the range for UV light, allowing for cross-links without denaturation. | 1 | Biochemistry |
STAT4 binds to hundreds of sites in the genome, among others to the promoters of genes for cytokines (IFN-γ, TNF), receptors (IL18R1, IL12rβ2, IL18RAP), and signaling factors (MYD88). | 1 | Biochemistry |
Real-life crime scene investigators and forensic scientists warn that popular television shows do not give a realistic picture of the work, often wildly distorting its nature, and exaggerating the ease, speed, effectiveness, drama, glamour, influence and comfort level of their jobs—which they describe as far more mundane, tedious and boring.
Some claim these modern TV shows have changed individuals' expectations of forensic science, sometimes unrealistically—an influence termed the "CSI effect".
Further, research has suggested that public misperceptions about criminal forensics can create, in the mind of a juror, unrealistic expectations of forensic evidence—which they expect to see before convicting—implicitly biasing the juror towards the defendant. Citing the "CSI effect," at least one researcher has suggested screening jurors for their level of influence from such TV programs. | 3 | Analytical Chemistry |
Numerous schemes have been described as artificial photosynthesis.
*Photocatalytic water splitting, the conversion water into hydrogen and oxygen:
This scheme is the simplest form of artificial photosynthesis conceptually, but has not been demonstrated in any practicable way.
*Light-driven carbon dioxide reduction, the conversion water, carbon dioxide into carbon monoxide or organic compounds and oxygen. In the conceptually simplest manifestation, this process gives CO:
Related processes give formic acid (HCO2H):
Variations might produce formaldehyde or, equivalently, carbohydrates:
These processes replicate natural carbon fixation.
Because of the socio-economic implications, Artificial photosynthesis is very topical, despite the many challenges.
Ideally the only inputs to produce such solar fuels would be water, carbon dioxide, and sunlight. The only by-product would be oxygen.
by using direct processes, | 5 | Photochemistry |
Commonly studied regulons in bacteria are those involved in response to stress such as heat shock. The heat shock response in E. coli is regulated by the sigma factor
σ32 (RpoH), whose regulon has been characterized as containing at least 89 open reading frames.
Regulons involving virulence factors in pathogenic bacteria are of particular research interest; an often-studied example is the phosphate regulon in E. coli, which couples phosphate homeostasis to pathogenicity through a two-component system. Regulons can sometimes be pathogenicity islands.
The Ada regulon in E. coli is a well-characterized example of a group of genes involved in the adaptive response form of DNA repair.
Quorum sensing behavior in bacteria is a commonly cited example of a modulon or stimulon, though some sources describe this type of intercellular auto-induction as a separate form of regulation. | 1 | Biochemistry |
LDH undergoes transcriptional regulation by PGC-1α. PGC-1α regulates LDH by decreasing LDH A mRNA transcription and the enzymatic activity of pyruvate to lactate conversion. | 1 | Biochemistry |
The Candelabro Trivulzio in the Milan Cathedral, a seven-branch bronze candlestick measuring 5 meters in height, has a base and lower part decorated with intricately designed ornament which is considered by many to be French work of the 13th century; the upper part with the branches was added in the second half of the 16th century. A portion of a similar object showing the same intricate decoration existed formerly at Reims, but was unfortunately destroyed during World War I.
In the 16th century the names of Germain Pilon and Jean Goujon are sufficient evidence of the ability to work in bronze. A great outburst of artistic energy is seen from the beginning of the 17th century, when works in ormolu or gilt bronze were produced in huge quantities. The craftsmanship is magnificent and of the highest quality, the designs at first refined and symmetrical; but later, under the influence of the rococo style, introduced in 1723, aiming only at gorgeous magnificence. It was all in keeping with the spirit of the age, and in their own sumptuous setting these fine candelabra, sconces, vases, clocks and rich mountings of furniture are entirely harmonious. The "ciseleur" and the "fondeur", such as Pierre Gouthière and Jacques Caffieri, associated themselves with the makers of fine furniture and of delicate Sèvres porcelain, the result being extreme richness and handsome effect. The style was succeeded after the French Revolution by a stiff, classical manner which, although having a charm of its own, lacks the life and freedom of earlier work. In London the styles may be studied in the Wallace collection, Manchester Square, and at the Victoria and Albert Museum, South Kensington; in New York at the Metropolitan Museum. | 8 | Metallurgy |
Affinity electrophoresis is a general name for many analytical methods used in biochemistry and biotechnology. Both qualitative and quantitative information may be obtained through affinity electrophoresis. Cross electrophoresis, the first affinity electrophoresis method, was created by Nakamura et al. Enzyme-substrate complexes have been detected using cross electrophoresis. The methods include the so-called electrophoretic mobility shift assay, charge shift electrophoresis and affinity capillary electrophoresis. The methods are based on changes in the electrophoretic pattern of molecules (mainly macromolecules) through biospecific interaction or complex formation. The interaction or binding of a molecule, charged or uncharged, will normally change the electrophoretic properties of a molecule. Membrane proteins may be identified by a shift in mobility induced by a charged detergent. Nucleic acids or nucleic acid fragments may be characterized by their affinity to other molecules. The methods have been used for estimation of binding constants, as for instance in lectin affinity electrophoresis or characterization of molecules with specific features like glycan content or ligand binding. For enzymes and other ligand-binding proteins, one-dimensional electrophoresis similar to counter electrophoresis or to "rocket immunoelectrophoresis", affinity electrophoresis may be used as an alternative quantification of the protein. Some of the methods are similar to affinity chromatography by use of immobilized ligands. | 1 | Biochemistry |
The pressure inside an ideal spherical bubble can be derived from thermodynamic free energy considerations. The above free energy can be written as:
where is the pressure difference between the inside (A) and outside (B) of the bubble, and is the bubble volume. In equilibrium, , and so,
For a spherical bubble, the volume and surface area are given simply by
and
Substituting these relations into the previous expression, we find
which is equivalent to the Young–Laplace equation when . | 6 | Supramolecular Chemistry |
The binding of the negatively charged nucleic acids to the positively charged iron particles occurs relatively fast. After complex formation, the loaded particles are incubated together with the target cells on a magnetic plate. The magnetic field causes the iron particles to be rapidly drawn towards the surface of the cell membrane. Cellular uptake occurs by either endocytosis or pinocytosis. Once delivered to the target cells, the DNA is released into the cytoplasm. The magnetic particles are accumulated in endosomes and/or vacuoles. Over time, the nanoparticles are degraded and the iron enters the normal iron metabolism. Influence of cellular functions by iron particles has not been reported yet. In most cases the increased iron concentration in culture media does not lead to cytotoxic effects. | 1 | Biochemistry |
The ionic strength of a solution is a measure of the concentration of ions in that solution. Ionic compounds, when dissolved in water, dissociate into ions. The total electrolyte concentration in solution will affect important properties such as the dissociation constant or the solubility of different salts. One of the main characteristics of a solution with dissolved ions is the ionic strength. Ionic strength can be molar (mol/L solution) or molal (mol/kg solvent) and to avoid confusion the units should be stated explicitly. The concept of ionic strength was first introduced by Lewis and Randall in 1921 while describing the activity coefficients of strong electrolytes. | 7 | Physical Chemistry |
Until the early 19th century, the usual method of producing wrought iron involved a charcoal-fired finery in a finery forge. In the beginning of the 19th century this became an obsolete process and was slowly replaced by the coal-fueled puddling process. However, charcoal continued to be used in some forges after most of the iron industry had abandoned it for coke.
In 1813 when John Bradley & Co. (whose leading partner was James Foster) took over forges at Eardington in Shropshire, a potting and stamping forge, they reverted to using charcoal. In 1820, he bought Hampton Loade Forge, which then became a tinplate works and in 1826 another charcoal forge. This was followed by other charcoal forges at Horsehay in 1832 and at the Old Park ironworks of the Botfield family about 1826. Cookley Forge in the Stour valley also reverted to charcoal working in 1814, supplying wire and tinplate mills.
By the 1830s, these forges were sometimes producing over 2000 tons of iron per year, compared with a few hundred from earlier finery forges. It is likely that these forges were using a more efficient variety of hearth, which from Swedish usage has come to be known as a Lancashire hearth. | 8 | Metallurgy |
Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids. Crystallography is a fundamental subject in the fields of materials science and solid-state physics (condensed matter physics). The word crystallography is derived from the Ancient Greek word (; "clear ice, rock-crystal"), and (; "to write"). In July 2012, the United Nations recognised the importance of the science of crystallography by proclaiming that 2014 would be the International Year of Crystallography.
Before the development of X-ray diffraction crystallography (see below), the study of crystals was based on physical measurements of their geometry using a goniometer. This involved measuring the angles of crystal faces relative to each other and to theoretical reference axes (crystallographic axes), and establishing the symmetry of the crystal in question. The position in 3D space of each crystal face is plotted on a stereographic net such as a Wulff net or Lambert net. The pole to each face is plotted on the net. Each point is labelled with its Miller index. The final plot allows the symmetry of the crystal to be established.
Crystallographic methods depend mainly on analysis of the diffraction patterns of a sample targeted by a beam of some type. X-rays are most commonly used; other beams used include electrons or neutrons. Crystallographers often explicitly state the type of beam used, as in the terms X-ray crystallography, neutron diffraction and electron diffraction. These three types of radiation interact with the specimen in different ways.
* X-rays interact with the spatial distribution of electrons in the sample.
* Neutrons are scattered by the atomic nuclei through the strong nuclear forces, but in addition, the magnetic moment of neutrons is non-zero. They are therefore also scattered by magnetic fields. When neutrons are scattered from hydrogen-containing materials, they produce diffraction patterns with high noise levels. However, the material can sometimes be treated to substitute deuterium for hydrogen. Because of these different forms of interaction, the three types of radiation are suitable for different crystallographic studies.
* Electrons are charged particles and therefore interact with the total charge distribution of both the atomic nuclei and the electrons of the sample.
It is hard to focus x-rays or neutrons, but since electrons are charged they can be focused and are used in electron microscope to produce magnified images. There are many ways that transmission electron microscopy and related techniques such as scanning transmission electron microscopy, high-resolution electron microscopy can be used to obtain images with in many cases atomic resolution from which crystallographic information can be obtained. There are also other methods such as low-energy electron diffraction, low-energy electron microscopy and reflection high-energy electron diffraction which can be used to obtain crystallographic information about surfaces. | 3 | Analytical Chemistry |
The quantity or concentration of an enzyme can be expressed in molar amounts, as with any other chemical, or in terms of activity in enzyme units. | 1 | Biochemistry |
The instrumentation needed to perform capillary electrophoresis is relatively simple. A basic schematic of a capillary electrophoresis system is shown in figure 1. The systems main components are a sample vial, source and destination vials, a capillary, electrodes, a high voltage power supply, a detector, and a data output and handling device. The source vial, destination vial and capillary are filled with an electrolyte such as an aqueous buffer solution. To introduce the sample, the capillary inlet is placed into a vial containing the sample. Sample is introduced into the capillary via capillary action, pressure, siphoning, or electrokinetically, and the capillary is then returned to the source vial. The migration of the analytes is initiated by an electric field that is applied between the source and destination vials and is supplied to the electrodes by the high-voltage power supply. In the most common mode of CE, all ions, positive or negative, are pulled through the capillary in the same direction by electroosmotic flow. The analytes separate as they migrate due to their electrophoretic mobility, and are detected near the outlet end of the capillary. The output of the detector is sent to a data output and handling device such as an integrator or computer. The data is then displayed as an electropherogram, which reports detector response as a function of time. Separated chemical compounds appear as peaks with different migration times in an electropherogram. The technique is often attributed to James W. Jorgensen and Krynn DeArman Lukacs, who first demonstrated the capabilities of this technique. Capillary electrophoresis was first combined with mass spectrometry by Richard D. Smith and coworkers, and provides extremely high sensitivity for the analysis of very small sample sizes. Despite the very small sample sizes (typically only a few nanoliters of liquid are introduced into the capillary), high sensitivity and sharp peaks are achieved in part due to injection strategies that result in a concentration of analytes into a narrow zone near the inlet of the capillary. This is achieved in either pressure or electrokinetic injections simply by suspending the sample in a buffer of lower conductivity (e.g.' lower salt concentration) than the running buffer. A process called field-amplified sample stacking (a form of isotachophoresis) results in concentration of analyte in a narrow zone at the boundary between the low-conductivity sample and the higher-conductivity running buffer.
To achieve greater sample throughput, instruments with arrays of capillaries are used to analyze many samples simultaneously. Such capillary array electrophoresis (CAE) instruments with 16 or 96 capillaries are used for medium- to high-throughput capillary DNA sequencing, and the inlet ends of the capillaries are arrayed spatially to accept samples directly from SBS-standard footprint 96-well plates. Certain aspects of the instrumentation (such as detection) are necessarily more complex than for a single-capillary system, but the fundamental principles of design and operation are similar to those shown in Figure 1. | 3 | Analytical Chemistry |
The CO ligand is often susceptible to attack by nucleophiles. For example, trimethylamine oxide and potassium bis(trimethylsilyl)amide convert CO ligands to CO and CN, respectively. In the "Hieber base reaction", hydroxide ion attacks the CO ligand to give a metallacarboxylic acid, followed by the release of carbon dioxide and the formation of metal hydrides or carbonylmetalates. A well-studied example of this nucleophilic addition is the conversion of iron pentacarbonyl to hydridoiron tetracarbonyl anion:
:Fe(CO) + NaOH → Na[Fe(CO)COH]
:Na[Fe(CO)COOH] + NaOH → Na[HFe(CO)] + NaHCO
Hydride reagents also attack CO ligands, especially in cationic metal complexes, to give the formyl derivative:
:[Re(CO)] + H → Re(CO)CHO
Organolithium reagents add with metal carbonyls to acylmetal carbonyl anions. O-Alkylation of these anions, such as with Meerwein salts, affords Fischer carbenes. | 0 | Organic Chemistry |
A linear biochemical pathway is a chain of enzyme-catalyzed reaction steps. The figure below shows a three step pathway, with intermediates, and . In order to sustain a steady-state, the boundary species and are fixed.
At steady-state the rate of reaction is the same at each step. This means there is an overall flux from X_o to X_1.
Linear pathways possess some well-known properties:
# Flux control is biased towards the first few steps of the pathway. Flux control shifts more to the first step as the equilibrium constants become large.
# Flux control is small at reactions close to equilibrium.
# Assuming reversibly, flux control at a given step is proportional to the product of the equilibrium constants. For example, flux control at the second step in a three step pathway is proportional to the product of the second and third equilibrium constants.
In all cases, a rationale for these behaviors is given in terms of how elasticities transmit changes through a pathway. | 1 | Biochemistry |
Sustained load cracking, or SLC, is a metallurgical phenomenon that occasionally develops in pressure vessels and structural components under stress for sustained periods of time.
It is particularly noted in aluminium pressure vessels such as diving cylinders.
Sustained load cracking is not a manufacturing defect; it is a phenomenon associated with certain alloys and service conditions:
*6351 aluminum alloy
*Overstressing due to excessive filling pressure
*Abuse and mechanical damage | 8 | Metallurgy |
Pyridine is not abundant in nature, except for the leaves and roots of belladonna (Atropa belladonna) and in marshmallow (Althaea officinalis). Pyridine derivatives, however, are often part of biomolecules such as alkaloids.
In daily life, trace amounts of pyridine are components of the volatile organic compounds that are produced in roasting and canning processes, e.g. in fried chicken, sukiyaki, roasted coffee, potato chips, and fried bacon. Traces of pyridine can be found in Beaufort cheese, vaginal secretions, black tea, saliva of those suffering from gingivitis, and sunflower honey. | 0 | Organic Chemistry |
The strength of a carboxylic acid depends on the extent of its ionization constant: the more ionized it is, the stronger it is. As an acid becomes stronger, the numerical value of its acid dissociation constant| drops.
In acids, the electron-releasing inductive effect of the alkyl group increases the electron density on oxygen and thus hinders the breaking of the O-H bond, which consequently reduces the ionization. Due to its greater ionization, formic acid () is stronger than acetic acid (). Monochloroacetic acid (), though, is stronger than formic acid, due to the electron-withdrawing effect of chlorine promoting ionization.
In benzoic acid, the carbon atoms which are present in the ring are sp hybridised. As a result, benzoic acid () is a stronger acid than cyclohexanecarboxylic acid (). Also, in aromatic carboxylic acids, electron-withdrawing groups substituted at the ortho and para positions can enhance the acid strength.
Since the carboxyl group is itself an electron-withdrawing group, dicarboxylic acids are, in general, stronger acids than their monocarboxyl analogues.
The Inductive effect will also help in polarization of a bond making certain carbon atom or other atom positions. | 7 | Physical Chemistry |
Lupeol is produced by several organisms from squalene epoxide. Dammarane and baccharane skeletons are formed as intermediates. The reactions are catalyzed by the enzyme lupeol synthase. A recent study on the metabolomics of Camellia japonica leaf revealed that lupeol is produced from squalene epoxide where squalene play the role as a precursor. | 0 | Organic Chemistry |
T7 RNA polymerase - taq polymerase - TATA box - taurochenodeoxycholate 6α-hydroxylase - taxadiene 5alpha-hydroxylase - taxane 10beta-hydroxylase - TAZ zinc finger - Tbf5 protein domain - technology transfer - template - termination codon - terminator - tertiary structure - tet resistance - TGF beta Activation - thymine - tissue-specific expression - tm - trans - trans-feruloyl-CoA hydratase - transcript - transcription - transcription factor - transcription/translation reaction - transcriptional start site - transfection - transformation (genetics) - transformation (with respect to bacteria) - transfection (with respect to cultured cells) - transgene - transgenic - transient transfection - transition - translation - transposition - transposon - transversion - triplet - trisomy - tRNA - tRNA (adenine-N1-)-methyltransferase - tRNA (guanine-N1-)-methyltransferase - TUG-UBL1 protein domain - tumor suppressor - tumor suppressor gene - | 1 | Biochemistry |
A batteryless radio is a radio receiver which does not require the use of a battery to provide it with electrical power.
Originally this referred to units which could be used directly by AC mains supply (mains radio); it can also refer to units which do not require a power source at all, except for the power that they receive from an ambient radio source, such as radio waves. | 7 | Physical Chemistry |
An assay is an analytic tool often used in a laboratory setting in order to assess or measure some quality of a target entity. In virology, assays can be used to differentiate between transformed and non-transformed cells. Varying the assay used, changes the selective pressure on the cells and therefore can change what properties are selected in the transformed cells.
Three common assays used are the focus forming assay, the Anchorage independent growth assay, and the reduced serum assay.
The focus forming assay (FFA) is used to grow cells containing a transforming oncogene on a monolayer of non-transformed cells. The transformed cells will form raised, dense spots on the sample as they grow without contact inhibition. This assay is highly sensitive compared to other assays used for viral analysis, such as the yield reduction assay.
An example of the Anchorage independent growth assay is the soft agar assay. The assay is assessing the cells' ability to grow in a gel or viscous fluid. Transformed cells can grow in this environment and are considered anchorage independent. Cells that can only grow when attached to a solid surface are anchorage dependent untransformed cells. This assay is considered one of the most stringent for detection of malignant transformation
In a reduced serum assay, cells are assayed by exploiting the changes in cell serum requirements. Non-transformed cells require at least a 5% serum medium in order to grow; however, transformed cells can grow in an environment with significantly less serum. | 1 | Biochemistry |
About 20 million kg per year are produced industrially as both a by-product of and precursor to the manufacture of Teflon. It is produced by reaction of chloroform with HF:
It is also generated biologically in small amounts apparently by decarboxylation of trifluoroacetic acid. | 2 | Environmental Chemistry |
At its annual meeting, AOAC presents a range of [https://www.aoac.org/membership/awards/ awards] for scientific excellence in standards development and for exceptional service to the association (including fellow). The association's highest honors include:
* The Harvey W. Wiley Award
* The William Horwitz Award | 3 | Analytical Chemistry |
The formation of a glycosidic linkage results in the formation of a new stereogenic centre and therefore a mixture of products may be expected to result. The linkage formed may either be axial or equatorial (α or β with respect to glucose). To better understand this, the mechanism of a glycosylation reaction must be considered. | 0 | Organic Chemistry |
The viral epitranscriptome includes all modifications to viral transcripts, studied by viral epitranscriptomics. Like the more general epitranscriptome, these modifications do not affect the sequence of the transcript, but rather have consequences on subsequent structures and functions. | 1 | Biochemistry |
Carbon tetraiodide is a tetrahalomethane with the molecular formula CI. Being bright red, it is a relatively rare example of a highly colored methane derivative. It is only 2.3% by weight carbon, although other methane derivatives are known with still less carbon. | 0 | Organic Chemistry |
The Exxon process, also Kuhlmann- or PCUK – oxo process, is used for the hydroformylation of C6–C12 olefins. The process relies on cobalt catalysts. In order to recover the catalyst, an aqueous sodium hydroxide solution or sodium carbonate is added to the organic phase. By extraction with olefin and neutralization by addition of sulfuric acid solution under carbon monoxide pressure the metal carbonyl hydride can recovered. This is stripped out with syngas, absorbed by the olefin, and returned to the reactor. Similar to the BASF process, the Exxon process is carried out at a pressure of about 30 MPa and at a temperature of about 160 to 180 °C. | 0 | Organic Chemistry |
A Morpholino, also known as a Morpholino oligomer and as a phosphorodiamidate Morpholino oligomer (PMO), is a type of oligomer molecule (colloquially, an oligo) used in molecular biology to modify gene expression. Its molecular structure contains DNA bases attached to a backbone of methylenemorpholine rings linked through phosphorodiamidate groups. Morpholinos block access of other molecules to small (~25 base) specific sequences of the base-pairing surfaces of ribonucleic acid (RNA). Morpholinos are used as research tools for reverse genetics by knocking down gene function.
This article discusses only the Morpholino antisense oligomers, which are nucleic acid analogs. The word "Morpholino" can occur in other chemical names, referring to chemicals containing a six-membered morpholine ring. To help avoid confusion with other morpholine-containing molecules, when describing oligos "Morpholino" is often capitalized as a trade name, but this usage is not consistent across scientific literature. Morpholino oligos are sometimes referred to as PMO (for phosphorodiamidate morpholino oligomer), especially in medical literature. Vivo-Morpholinos and PPMO are modified forms of Morpholinos with chemical groups covalently attached to facilitate entry into cells.
Gene knockdown is achieved by reducing the expression of a particular gene in a cell. In the case of protein-coding genes, this usually leads to a reduction in the quantity of the corresponding protein in the cell. Knocking down gene expression is a method for learning about the function of a particular protein; in a similar manner, causing a specific exon to be spliced out of the RNA transcript encoding a protein can help to determine the function of the protein moiety encoded by that exon or can sometimes knock down the protein activity altogether. These molecules have been applied to studies in several model organisms, including mice, zebrafish, frogs and sea urchins. Morpholinos can also modify the splicing of pre-mRNA or inhibit the maturation and activity of miRNA. Techniques for targeting Morpholinos to RNAs and delivering Morpholinos into cells have recently been reviewed in a journal article and in book form.
Morpholinos are in development as pharmaceutical therapeutics targeted against pathogenic organisms such as bacteria or viruses and genetic diseases. A Morpholino-based drug eteplirsen from Sarepta Therapeutics received accelerated approval from the US Food and Drug Administration in September 2016 for the treatment of some mutations causing Duchenne muscular dystrophy, although the approval process was mired in controversy. Other Morpholino-based drugs golodirsen, viltolarsen, and casimersen (also for Duchenne muscular dystrophy) were approved by the FDA in 2019–2021. | 1 | Biochemistry |
IgE antibodies against plant/insect CCD determinants were shown to have both strict specificity and high affinity, so in principle they might be expected to lead to clinical symptoms just as habitual for anti-peptide IgE. In vitro experiments (histamine-release tests) with polyvalent glyco-allergens corroborated this view. Provocation tests with patients as well as empirical evidence however, indicate that CCDs never cause any ponderable allergic symptoms. It is assumed that the frequent contact with CCD containing foods induces tolerance akin a specific immune therapy. | 0 | Organic Chemistry |
Solid-state ionics is the study of ionic-electronic mixed conductor and fully ionic conductors (solid electrolytes) and their uses. Some materials that fall into this category include inorganic crystalline and polycrystalline solids, ceramics, glasses, polymers, and composites. Solid-state ionic devices, such as solid oxide fuel cells, can be much more reliable and long-lasting, especially under harsh conditions, than comparable devices with fluid electrolytes.
The field of solid-state ionics was first developed in Europe, starting with the work of Michael Faraday on solid electrolytes AgS and PbF in 1834. Fundamental contributions were later made by Walther Nernst, who derived the Nernst equation and detected ionic conduction in heterovalently doped zirconia, which he applied in his Nernst lamp. Another major step forward was the characterization of silver iodide in 1914. Around 1930, the concept of point defects was established by Yakov Frenkel, Walter Schottky and Carl Wagner, including the development of point-defect thermodynamics by Schottky and Wagner; this helped explain ionic and electronic transport in ionic crystals, ion-conducting glasses, polymer electrolytes and nanocomposites. In the late 20th and early 21st centuries, solid-state ionics focused on the synthesis and characterization of novel solid electrolytes and their applications in solid state battery systems, fuel cells and sensors.
The term solid state ionics was coined in 1967 by Takehiko Takahashi, but did not become widely used until the 1980s, with the emergence of the journal Solid State Ionics. The first international conference on this topic was held in 1972 in Belgirate, Italy, under the name "Fast Ion Transport in Solids, Solid State Batteries and Devices". | 7 | Physical Chemistry |
Whereas Gram-negative bacteria primarily use acylated homoserine lactones, Gram-positive bacteria generally use oligopeptides as autoinducers for quorum sensing. These molecules are often synthesized as larger polypeptides that are cleaved post-translationally to produce “processed” peptides. Unlike AHLs that can freely diffuse across cell membranes, peptide autoinducers usually require specialized transport mechanisms (often ABC transporters). Additionally, they do not freely diffuse back into cells, so bacteria that use them must have mechanisms to detect them in their extracellular environments. Most Gram-positive bacteria use a two-component signaling mechanism in quorum sensing. Secreted peptide autoinducers accumulate as a function of cell density. Once a quorum level of autoinducer is achieved, its interaction with a sensor kinase at the cell membrane initiates a series of phosphorylation events that culminate in the phosphorylation of a regulator protein intracellularly. This regulator protein subsequently functions as a transcription factor and alters gene expression. Similar to Gram-negative bacteria, the autoinduction and quorum sensing system in Gram-positive bacteria is conserved, but again, individual species have tailored specific aspects for surviving and communicating in unique niche environments. | 1 | Biochemistry |
As mentioned above, is one of the most common formulations for the thermal pressure coefficient.
Both and are affected by temperature changes, but the value of and of a solid much less sensitive to temperature change above its Debye temperature. Thus, the thermal pressure of a solid due to moderate temperature change above the Debye temperature can be approximated by assuming a constant value of and .
On the contrary, in the paper, authors demonstrated that, at ambient pressure, the pressure predicted of Au and MgO from a constant value of deviates from the experimental data, and the higher temperature, the more deviation. In addition, the authors suggested a thermal expansion model to replace the thermal pressure model. | 7 | Physical Chemistry |
Eukaryotic genomes are ubiquitously associated into chromatin; however, cells must spatially and temporally regulate specific loci independently of bulk chromatin. In order to achieve the high level of control required to co-ordinate nuclear processes such as DNA replication, repair, and transcription, cells have developed a variety of means to locally and specifically modulate chromatin structure and function. This can involve covalent modification of histones, the incorporation of histone variants, and non-covalent remodelling by ATP-dependent remodeling enzymes. | 1 | Biochemistry |
Compared to thiols (R-S-H), persulfides are uncommon. They are thermodynamically unstable with respect to loss of elemental sulfur:
:RSSH → RSH + 1/8 S
Nonetheless, persulfides are often kinetically stable.
The S-H bond is both more acidic and more fragile than in thiols. This can be seen in the bond dissociation energy of a typical persulfide, which is 22 kcal/mol weaker than a typical thiol, and the lower pK of about 6.2 for persulfides compared to 7.5 for thiols. Thus, persulfides exist predominantly in the ionized form at neutral pH. This effect is attributed to the stability of the RSS· radical. | 0 | Organic Chemistry |
Small quantities of hydrogen present inside certain metallic materials make the latter brittle and susceptible to sub-critical crack growth under stress. Hydrogen embrittlement may occur as a side effect of electroplating processes.
Delayed failure is the fracture of a component under stress after an elapsed time, is a characteristic feature of hydrogen embrittlement (2). Hydrogen entry into the material may be effected during plating, pickling, phosphating, melting, casting or welding. Corrosion during service in moist environments generates hydrogen, part of which may enter the metal as atomic hydrogen (H) and cause embrittlement. Presence of a tensile stress, either inherent or externally applied, is necessary for metals to be damaged. As in the case of stress corrosion cracking, hydrogen embrittlement may also lead to a decrease in the threshold stress intensity factor for crack propagation or an increase in the sub-critical crack growth velocity of the material. The most visible effect of hydrogen in materials is a drastic reduction in ductility during tensile tests. It may increase, decrease or leave unaffected the yield strength of the material.
Hydrogen may also cause serrated yielding in certain metals such as niobium, nickel and some steels (3). | 8 | Metallurgy |
Insulators have two main functions:
# Enhancer-blocking insulators prevent distal enhancers from acting on the promoter of neighbouring genes
# Barrier insulators prevent silencing of euchromatin by the spread of neighbouring heterochromatin
While enhancer-blocking is classified as an inter-chromosomal interaction, acting as a barrier is classified as an intra-chromosomal interaction. The need for insulators arises where two adjacent genes on a chromosome have very different transcription patterns; it is critical that the inducing or repressing mechanisms of one do not interfere with the neighbouring gene. Insulators have also been found to cluster at the boundaries of topologically associating domains (TADs) and may have a role in partitioning the genome into "chromosome neighborhoods" - genomic regions within which regulation occurs.
Some insulators can act as both enhancer blocker and barriers, and some just have one of the two functions. Some examples of different insulators are:
* Drosophila melanogaster insulators gypsy and scs scs are both enhancer-blocking insulators
* Gallus gallus have insulators, Lys 5 A that have both enhancer-blocking and barrier activity, as well as HS4' that have only enhancer-blocking activity
* Saccharomyces cerevisiae insulators STAR and UAS are both barrier insulators
* Homo sapiens HS5 insulator acts as an enhancer-blocker | 1 | Biochemistry |
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