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Entropic gravity, also known as emergent gravity, is a theory in modern physics that describes gravity as an entropic force—a force with macro-scale homogeneity but which is subject to quantum-level disorder—and not a fundamental interaction. The theory, based on string theory, black hole physics, and quantum information theory, describes gravity as an emergent phenomenon that springs from the quantum entanglement of small bits of spacetime information. As such, entropic gravity is said to abide by the second law of thermodynamics under which the entropy of a physical system tends to increase over time.
The theory has been controversial within the physics community but has sparked research and experiments to test its validity. | 7 | Physical Chemistry |
The importance of motor proteins in cells becomes evident when they fail to fulfill their function. For example, kinesin deficiencies have been identified as the cause for Charcot-Marie-Tooth disease and some kidney diseases. Dynein deficiencies can lead to chronic infections of the respiratory tract as cilia fail to function without dynein. Numerous myosin deficiencies are related to disease states and genetic syndromes. Because myosin II is essential for muscle contraction, defects in muscular myosin predictably cause myopathies. Myosin is necessary in the process of hearing because of its role in the growth of stereocilia so defects in myosin protein structure can lead to Usher syndrome and non-syndromic deafness. | 6 | Supramolecular Chemistry |
Optical transitions must preserve the total spin and occur only between levels of the same total spin. Specifically, transitions between the ground and excited states (with equal spin) can be induced using a green laser with a wavelength of 546 nm. Transitions E→A and E→A are non-radiative, while A →E has both a non-radiative and infrared decay path.
The diagram on the right shows the multi-electronic states of the NV center labeled according to their symmetry (E or A) and their spin state (3 for a triplet (S=1) and 1 for a singlet (S=0)). There are two triplet states and two intermediate singlet states. | 7 | Physical Chemistry |
Relaxivities, nuclear relaxation rates, line shape and other parameters were reported useful in structural studies of carbohydrates. | 0 | Organic Chemistry |
The lac operon in the prokaryote E. coli consists of genes that produce enzymes to break down lactose. Its operon is an example of a prokaryotic silencer. The three functional genes in this operon are lacZ, lacY, and lacA. The repressor gene, lacI, will produce the repressor protein LacI which is under allosteric regulation. These genes are activated by the presence of lactose in the cell which acts as an effector molecule that binds to LacI. When the repressor is bound to lactose, it will not bind to the operator, which allows RNA polymerase to bind to the promoter to initiate transcription of the operon. When the repressors allosteric site is not bound to lactose, its active site will bind to the operator to prevent RNA polymerase from transcribing the genes of the lac' operon. | 1 | Biochemistry |
Since a variety of systems have been investigated, a study was done to investigate the individual adsorption of a mixed solution. This phenomenon is also called competitive adsorption because solutes tend to compete for the same adsorption sites. In the experiment conducted by Rosene and Manes, the competitive adsorption of glucose, urea, benzoic acid, phthalide, and p-nitrophenol. Using the Polanyi adsorption model, they were able to calculate the relative adsorption of each compound onto the surface of activated carbon. | 7 | Physical Chemistry |
The working of memorial brasses is generally considered to have originated in north-western Germany, at least one centre being Cologne, where were manufactured the latten or Cullen plates for local use and for exportation. But it is certain that from medieval times there was an equal production in the towns of Belgium, when brass was the favoured metal for other purposes. Continental brasses were of rectangular sheets of metal on which the figure of the deceased was represented, up to life-size, by deeply incised lines, frequently filled with mastic or enamel-like substance; the background of the figures was covered with an architectural setting, or with ornament of foliage and figures, and an inscription. In England, possibly because the metal was less plentiful, the figures are usually accessories, being cut out of the metal and inserted in the matrices of stone or marble slabs which form part of the tomb; architectural canopies, inscriptions and shields of arms are affixed in the same way. Thus the stone or marble background takes the place of the decorated brass background of the Continental example. The early method of filling in the incisions has suggested some connection with the methods of the Limoges enamellers of the 13th century. The art was introduced into England from the Low Countries, and speedily attained a high degree of excellence. For many centuries it remained very popular, and a large number of brasses still remain to witness to a very beautiful department of artistic working.
The earliest existing brass is that of Bishop Ysowilpe at Verden, in Germany, which dates from 1231 and is on the model of an incised stone, as if by an artist accustomed to work in that material. In England the oldest example is at Stoke DAbernon church, in Surrey, to the memory of Sir John DAbernon, who died in 1277. Numerous brasses are to be found in Belgium, and some in France and the Netherlands. Apart from their artistic attractiveness, these ornamental brasses are of the utmost value in faithfully depicting the costumes of the period, ecclesiastical, civil or military; they furnish also appropriate inscriptions in beautiful lettering (cf. Brass Gallery). | 8 | Metallurgy |
In C4 plants, sodium is a micronutrient that aids in metabolism, specifically in regeneration of phosphoenolpyruvate (involved in the biosynthesis of various aromatic compounds, and in carbon fixation) and synthesis of chlorophyll. In others, it substitutes for potassium in several roles, such as maintaining turgor pressure and aiding in the opening and closing of stomata. Excess sodium in the soil limits the uptake of water due to decreased water potential, which may result in wilting; similar concentrations in the cytoplasm can lead to enzyme inhibition, which in turn causes necrosis and chlorosis. To avoid these problems, plants developed mechanisms that limit sodium uptake by roots, store them in cell vacuoles, and control them over long distances; excess sodium may also be stored in old plant tissue, limiting the damage to new growth. Though much how excess sodium loading in the xylem is yet to be determined. However, anti porter CHX21 can be attributed to active loading of sodium into the xylem. | 1 | Biochemistry |
This explanation proposes that a stable product could contribute to the alpha effect, however, this factor could not be the sole factor. | 7 | Physical Chemistry |
Max Planck derived a formula to describe the electromagnetic field inside a box when in thermal equilibrium in 1900.
His model consisted of a superposition of standing waves. In one dimension, the box has length L, and only sinusoidal waves of wavenumber
can occur in the box, where n is a positive integer (mathematically denoted by ). The equation describing these standing waves is given by:
where E is the magnitude of the electric field amplitude, and E is the magnitude of the electric field at position x. From this basic, Planck's law was derived.
In 1911, Ernest Rutherford concluded, based on alpha particle scattering, that an atom has a central pointlike proton. He also thought that an electron would be still attracted to the proton by Coulomb's law, which he had verified still held at small scales. As a result, he believed that electrons revolved around the proton. Niels Bohr, in 1913, combined the Rutherford model of the atom with the quantisation ideas of Planck. Only specific and well-defined orbits of the electron could exist, which also do not radiate light. In jumping orbit the electron would emit or absorb light corresponding to the difference in energy of the orbits. His prediction of the energy levels was then consistent with observation.
These results, based on a discrete set of specific standing waves, were inconsistent with the continuous classical oscillator model.
Work by Albert Einstein in 1905 on the photoelectric effect led to the association of a light wave of frequency with a photon of energy . In 1917 Einstein created an extension to Bohrs model by the introduction of the three processes of stimulated emission, spontaneous emission and absorption (electromagnetic radiation). | 7 | Physical Chemistry |
Induction of proliferation by the EpoR is likely cell type-dependent. It is known that EpoR can activate mitogenic signaling pathways and can lead to cell proliferation in erythroleukemic cell lines in vitro, various non-erythroid cells, and cancer cells. So far, there is no sufficient evidence that in vivo, EpoR signaling can induce erythroid progenitors to undergo cell division, or whether Epo levels can modulate the cell cycle. EpoR signaling may still have a proliferation effect upon BFU-e progenitors, but these progenitors cannot be directly identified, isolated and studied. CFU-e progenitors enter the cell cycle at the time of GATA-1 induction and PU.1 suppression in a developmental manner rather than due to EpoR signaling. Subsequent differentiation stages (proerythroblast to orthochromatic erythroblast) involve a decrease in cell size and eventual expulsion of the nucleus, and are likely dependent upon EpoR signaling only for their survival. In addition, some evidence on macrocytosis in hypoxic stress (when Epo can increase 1000-fold) suggests that mitosis is actually skipped in later erythroid stages, when EpoR expression is low/absent, in order to provide emergency reserve of red blood cells as soon as possible. Such data, though sometimes circumstantial, argue that there is limited capacity to proliferate specifically in response to Epo (and not other factors). Together, these data suggest that EpoR in erythroid differentiation may function primarily as a survival factor, while its effect on the cell cycle (for example, rate of division and corresponding changes in the levels of cyclins and Cdk inhibitors) in vivo awaits further work. In other cell systems, however, EpoR may provide a specific proliferative signal. | 1 | Biochemistry |
* Aronson, S. and Ludlam, T.: [https://searchworks.stanford.edu/view/11327941 "Hunting the quark gluon plasma"], U.S. Dept. of Energy (2005)
* Letessier, Jean: [https://searchworks.stanford.edu/view/4807502 Hadrons and quark-gluon plasma], Cambridge monographs on particle physics, nuclear physics, and cosmology (Vol. 18), Cambridge University Press (2002) | 7 | Physical Chemistry |
The principal natural phenomena that contribute acid-producing gases to the atmosphere are emissions from volcanoes. Thus, for example, fumaroles from the Laguna Caliente crater of Poás Volcano create extremely high amounts of acid rain and fog, with acidity as high as a pH of 2, clearing an area of any vegetation and frequently causing irritation to the eyes and lungs of inhabitants in nearby settlements. Acid-producing gasses are also created by biological processes that occur on the land, in wetlands, and in the oceans. The major biological source of sulfur compounds is dimethyl sulfide.
Nitric acid in rainwater is an important source of fixed nitrogen for plant life, and is also produced by electrical activity in the atmosphere such as lightning.
Acidic deposits have been detected in glacial ice thousands of years old in remote parts of the globe. | 2 | Environmental Chemistry |
This classification, based on the effects on behavior, remains artificial. Pheromones fill many additional functions.
* Nasonov pheromones (worker bees)
* Royal pheromones (bees)
* Calming (appeasement) pheromones (mammals)
* Necromones, given off by a deceased and decomposing organism; consisting of oleic and linoleic acids, they allow crustaceans and hexapods to identify the presence of dead conspecifics.
* Suckling: TAA is present in rabbit milk and seems to play a role of pheromone inducing suckling in the newborn rabbit. | 1 | Biochemistry |
The SUPERFAMILY database has numerous research applications and has been used by many research groups for various studies. It can serve either as a database for proteins that the user wishes to examine with other methods, or to assign a function and structure to a novel or uncharacterized protein. One study found SUPERFAMILY to be very adept at correctly assigning an appropriate function and structure to a large number of domains of unknown function by comparing them to the databases hidden Markov models. Another study used SUPERFAMILY to generate a data set of 1,733 Fold superfamily domains (FSF) in use of a comparison of proteomes and functionomes for to identify the origin of cellular diversification. | 1 | Biochemistry |
The size and strength of the induced vortices around a conducting particle have direct relationship with the applied electric filed and also the size of the conducted surface. This phenomenon is experimentally and numerically proven by several studies. The vortices grow as the external electric field increases and generate "sinkhole" at the center of the each vortex while circulates the fluid faster. It is demonstrated that increasing the size of the conducting surface forms bigger induced vortices to the point that geometry does not limits this grows. | 7 | Physical Chemistry |
ESI interface for LC–MS systems was developed by Fenn and collaborators in 1988. This ion source/ interface can be used for the analysis of moderately polar and even very polar molecules (e.g., metabolites, xenobiotics, peptides, nucleotides, polysaccharides). The liquid eluate coming out of the LC column is directed into a metal capillary kept at 3 to 5 kV and is nebulized by a high-velocity coaxial flow of gas at the tip of the capillary, creating a fine spray of charged droplets in front of the entrance to the vacuum chamber. To avoid contamination of the vacuum system by buffers and salts, this capillary is usually perpendicularly located at the inlet of the MS system, in some cases with a counter-current of dry nitrogen in front of the entrance through which ions are directed by the electric field. In some sources, rapid droplet evaporation and thus maximum ion emission is achieved by mixing an additional stream of hot gas with the spray plume in front of the vacuum entrance. In other sources, the droplets are drawn through a heated capillary tube as they enter the vacuum, promoting droplet evaporation and ion emission. These methods of increasing droplet evaporation now allow the use of liquid flow rates of 1 - 2 mL/min to be used while still achieving efficient ionisation and high sensitivity. Thus while the use of 1 – 3 mm microbore columns and lower flow rates of 50 - 200 μl/min was commonly considered necessary for optimum operation, this limitation is no longer as important, and the higher column capacity of larger bore columns can now be advantageously employed with ESI LC–MS systems. Positively and negatively charged ions can be created by switching polarities, and it is possible to acquire alternate positive and negative mode spectra rapidly within the same LC run . While most large molecules (greater than MW 1500–2000) produce multiply charged ions in the ESI source, the majority of smaller molecules produce singly charged ions. | 3 | Analytical Chemistry |
Hexamethyldisilazane is employed as a reagent in many organic reactions:
1) HMDS is used as a reagent in condensation reactions of heterocyclic compounds such as in the microwave synthesis of a derivative of xanthine:
2) The HMDS mediated trimethylsilylation of alcohols, thiols, amines and amino acids as protective groups or for intermediary organosilicon compounds is found to be very efficient and replaced TMSCl reagent.
Silylation of glutamic acid with excess hexamethyldisilazane and catalytic TMSCl in either refluxing xylene or acetonitrile followed by dilution with alcohol (methanol or ethanol) yields the derived lactam pyroglutamic acid in good yield.
HMDS in the presence of catalytic iodine facilitates the silylation of alcohols in excellent yields.
3) HMDS can be used to silylate laboratory glassware and make it hydrophobic, or automobile glass, just as Rain-X does.
4) In gas chromatography, HMDS can be used to silylate OH groups of organic compounds to increase volatility, this way enabling GC-analysis of chemicals that are otherwise non-volatile. | 0 | Organic Chemistry |
A number of chelators of divalent cations have different fluorescence spectra in the bound and unbound states. Chelators for Ca are well established, have high affinity for the cation, and low interference from other ions. Mg chelators lag behind and the major fluorescence dye for Mg (mag-fura 2) actually has a higher affinity for Ca. This limits the application of this dye to cell types where the resting level of Ca is is to be measured. Recently, Otten et al. (2001) have described work into a new class of compounds that may prove more useful, having significantly better binding affinities for Mg. The use of the fluorescent dyes is limited to measuring the free Mg. If the ion concentration is buffered by the cell by chelation or removal to subcellular compartments, the measured rate of uptake will give only minimum values of km and Vmax. | 1 | Biochemistry |
The digestive system is supplied by the celiac artery. The celiac artery is the first major branch from the abdominal aorta, and is the only major artery that nourishes the digestive organs.
There are three main divisions – the left gastric artery, the common hepatic artery and the splenic artery.
The celiac artery supplies the liver, stomach, spleen and the upper 1/3 of the duodenum (to the sphincter of Oddi) and the pancreas with oxygenated blood. Most of the blood is returned to the liver via the portal venous system for further processing and detoxification before returning to the systemic circulation via the hepatic veins.
The next branch from the abdominal aorta is the superior mesenteric artery, which supplies the regions of the digestive tract derived from the midgut, which includes the distal 2/3 of the duodenum, jejunum, ileum, cecum, appendix, ascending colon, and the proximal 2/3 of the transverse colon.
The final branch which is important for the digestive system is the inferior mesenteric artery, which supplies the regions of the digestive tract derived from the hindgut, which includes the distal 1/3 of the transverse colon, descending colon, sigmoid colon, rectum, and the anus above the pectinate line.
Blood flow to the digestive tract reaches its maximum 20–40 minutes after a meal and lasts for 1.5–2 hours. | 1 | Biochemistry |
Consider the set of active centers (fig.1.). Assume fast transition between sublevels within each level, and slow transition between levels.
According to the McCumber hypothesis, the cross-sections and do not depend on the populations and .
Therefore, we can deduce the relation, assuming the thermal state.
Let be group velocity of light in the medium, the product is spectral rate of
stimulated emission, and is that of absorption; is spectral rate of spontaneous emission. (Note that in this approximation, there is no such thing as a spontaneous absorption)
The balance of photons gives:
Which can be rewritten as
The thermal distribution of density of photons follows from blackbody radiation
Both (4) and (5) hold for all frequencies . For the case of idealized two-level active centers, , and , which leads to the relation between the spectral rate of spontaneous emission and the emission cross-section . (We keep the term probability of emission for the quantity , which is probability of emission of a photon within small spectral interval during a short time interval , assuming that at time the atom is excited.) The relation (D2) is a fundamental property of spontaneous and stimulated emission, and perhaps the only way to prohibit a spontaneous break of the thermal equilibrium in the thermal state of excitations and photons.
For each site number , for each sublevel number , the partial spectral emission probability can be expressed from consideration of idealized two-level atoms:
Neglecting the cooperative coherent effects, the emission is additive: for any concentration of sites and for any partial population of sublevels, the same proportionality between and holds for the effective cross-sections:
Then, the comparison of (D1) and (D2) gives the relation
This relation is equivalent of the McCumber relation (mc), if we define the zero-line frequency as solution of equation
the subscript indicates that the ratio of populations in evaluated in the thermal state. The zero-line frequency can be expressed as
Then (n1n2) becomes equivalent of the McCumber relation (mc).
No specific property of sublevels of active medium is required to keep the McCumber relation. It follows from the assumption about quick transfer of energy among excited laser levels and among lower laser levels. The McCumber relation (mc) has the same range of validity as the concept of the emission cross-section
itself. | 7 | Physical Chemistry |
Alternative splicing was first observed in 1977. The adenovirus produces five primary transcripts early in its infectious cycle, prior to viral DNA replication, and an additional one later, after DNA replication begins. The early primary transcripts continue to be produced after DNA replication begins. The additional primary transcript produced late in infection is large and comes from 5/6 of the 32kb adenovirus genome. This is much larger than any of the individual adenovirus mRNAs present in infected cells. Researchers found that the primary RNA transcript produced by adenovirus type 2 in the late phase was spliced in many different ways, resulting in mRNAs encoding different viral proteins. In addition, the primary transcript contained multiple polyadenylation sites, giving different 3’ ends for the processed mRNAs.
In 1981, the first example of alternative splicing in a transcript from a normal, endogenous gene was characterized. The gene encoding the thyroid hormone calcitonin was found to be alternatively spliced in mammalian cells. The primary transcript from this gene contains 6 exons; the calcitonin mRNA contains exons 1–4, and terminates after a polyadenylation site in exon 4. Another mRNA is produced from this pre-mRNA by skipping exon 4, and includes exons 1–3, 5, and 6. It encodes a protein known as CGRP (calcitonin gene related peptide). Examples of alternative splicing in immunoglobin gene transcripts in mammals were also observed in the early 1980s.
Since then, many other examples of biologically relevant alternative splicing have been found in eukaryotes. The "record-holder" for alternative splicing is a D. melanogaster gene called Dscam, which could potentially have 38,016 splice variants.
In 2021, it was discovered that the genome of adenovirus type 2, the adenovirus in which alternative splicing was first identified, was able to produce a much greater variety of mRNA than previously thought. By using next generation sequencing technology, researchers were able to update the human adenovirus type 2 transcriptome, and present a mind-boggling 904 unique mRNA, produced by the virus through a complex pattern of alternative splicing. Very few of these splice variants have been shown to be functional, a point that the authors raise in their paper.
::"An outstanding question is what roles the menagerie of novel RNAs play or whether they are spurious molecules generated by an overloaded splicing machinery." | 1 | Biochemistry |
Gene expression is regulated by histone acetylation and deacetylation, and this regulation is also applicable to inflammatory genes. Inflammatory lung diseases are characterized by expression of specific inflammatory genes such as NF-κB and AP-1 transcription factor. Treatments with corticosteroids and theophylline for inflammatory lung diseases interfere with HAT/HDAC activity to turn off inflammatory genes.
Specifically, gene expression data demonstrated increased activity of HAT and decreased level of HDAC activity in patients with Asthma. Patients with chronic obstructive pulmonary disease showed there is an overall decrease in HDAC activity with unchanged levels of HAT activity. Results have shown that there is an important role for HAT/HDAC activity balance in inflammatory lung diseases and provided insights on possible therapeutic targets. | 0 | Organic Chemistry |
* First position – primary direction – z direction, assigned to the higher-order axis.
* Second position – symmetrically equivalent secondary directions, which are perpendicular to the z-axis. These can be 2, m, or
* Third position – symmetrically equivalent tertiary directions, passing between secondary directions. These can be 2, m, or
These are the crystallographic groups 3, 32, 3m, , and (trigonal crystal system), 4, 422, 4mm, , 2m, , and (tetragonal), and 6, 622, 6mm, , m2, , and (hexagonal). Analogously, symbols of non-crystallographic groups (with axes of order 5, 7, 8, 9, ...) can be constructed. These groups can be arranged in the following table
It can be noticed that in groups with odd-order axes n and the third position in symbol is always absent, because all n directions, perpendicular to higher-order axis, are symmetrically equivalent. For example, in the picture of a triangle all three mirror planes (S, S, S) are equivalent – all of them pass through one vertex and the center of the opposite side.
For even-order axes n and there are secondary directions and tertiary directions. For example, in the picture of a regular hexagon one can distinguish two sets of mirror planes – three planes go through two opposite vertexes, and three other planes go through the centers of opposite sides. In this case any of two sets can be chosen as secondary directions, the rest set will be tertiary directions. Hence groups 2m, 2m, 2m, ... can be written as m2, m2, m2, ... . For symbols of point groups this order usually doesnt matter; however, it will be important for Hermann–Mauguin symbols of corresponding space groups, where secondary directions are directions of symmetry elements along unit cell translations b and c, while the tertiary directions correspond to the direction between unit cell translations b and c. For example, symbols Pm2 and P2m denote two different space groups. This also applies to symbols of space groups with odd-order axes 3 and . The perpendicular symmetry elements can go along unit cell translations b and c' or between them. Space groups P321 and P312 are examples of the former and the latter cases, respectively.
The symbol of point group may be confusing; the corresponding Schoenflies symbol is D, which means that the group consists of 3-fold axis, three perpendicular 2-fold axes, and 3 vertical diagonal planes passing between these 2-fold axes, so it seems that the group can be denoted as 32m or 3m2. However, one should remember that, unlike Schoenflies notation, the direction of a plane in a Hermann–Mauguin symbol is defined as the direction perpendicular to the plane, and in the D group all mirror planes are perpendicular to 2-fold axes, so they should be written in the same position as . Second, these complexes generate an inversion center, which combining with the 3-fold rotation axis generates a rotoinversion axis.
Groups with n = ∞ are called limit groups or Curie groups. | 3 | Analytical Chemistry |
Post-mortem diagnosis is the use of post-mortem chemistry analysis tests to diagnose a disease after someone has died. Some diseases are unknown until death, or were not correctly diagnosed earlier. One way that diseases can be diagnosed is by examining the concentrations of certain substances in the blood or other sample types. For example, diabetic ketoacidosis can be diagnosed by looking at the concentration glucose levels in the vitreous humor, ketone bodies, glycated hemoglobin, or glucose in the urine. Dehydration can be diagnosed by looking for increased urea nitrogen, sodium, and chloride levels, with normal creatinine levels in the vitreous humor. Endocrine disorders can be diagnosed by looking at hormone concentrations and epinephrine and insulin levels. Liver diseases can be diagnosed by looking at the ratio of albumin and globulin in the sample.
<br /> | 1 | Biochemistry |
There have also been limited studies on using these materials in robotics, for example the hobbyist robot Stiquito (and "Roboterfrau Lara"), as they make it possible to create very lightweight robots. Recently, a prosthetic hand was introduced by Loh et al. that can almost replicate the motions of a human hand [Loh2005]. Other biomimetic applications are also being explored. Weak points of the technology are energy inefficiency, slow response times, and large hysteresis. | 8 | Metallurgy |
Free triiodothyronine (fT or free T3) is generally elevated in hyperthyroidism and decreased in hypothyroidism.
Reference ranges depend on the method of analysis. Results should always be interpreted using the range from the laboratory that performed the test. Example values are: | 1 | Biochemistry |
A particularly vexing question in the study of the chemical origins of life is the selection of ribose, which forms the backbone of the nucleic acids found in modern biological systems. Eschenmoser's work on a variant of the formose reaction that produces phosphorylated ribose in relatively significant concentrations has provided significant insight. Eschenmoser and colleagues demonstrated that phosphorylated glycolaldehyde when condensed with glyceraldehyde (a product of successive formaldehyde condensations) produces phosphorylated ribose differentially, providing a plausible explanation for the origin of both the sugar ribose, and the phosphate group required to polymerize monomeric nucleotides, in modern biochemistry. | 0 | Organic Chemistry |
In chemical synthesis, click chemistry is a class of simple, atom-economy reactions commonly used for joining two molecular entities of choice. Click chemistry is not a single specific reaction, but describes a way of generating products that follow examples in nature, which also generates substances by joining small modular units. In many applications, click reactions join a biomolecule and a reporter molecule. Click chemistry is not limited to biological conditions: the concept of a "click" reaction has been used in chemoproteomic, pharmacological, biomimetic and molecular machinery applications. However, they have been made notably useful in the detection, localization and qualification of biomolecules.
Click reactions occur in one pot, are not disturbed by water, generate minimal and inoffensive byproducts, and are "spring-loaded"—characterized by a high thermodynamic driving force that drives it quickly and irreversibly to high yield of a single reaction product, with high reaction specificity (in some cases, with both regio- and stereo-specificity). These qualities make click reactions particularly suitable to the problem of isolating and targeting molecules in complex biological environments. In such environments, products accordingly need to be physiologically stable and any byproducts need to be non-toxic (for in vivo systems).
By developing specific and controllable bioorthogonal reactions, scientists have opened up the possibility of hitting particular targets in complex cell lysates. Recently, scientists have adapted click chemistry for use in live cells, for example using small molecule probes that find and attach to their targets by click reactions. Despite challenges of cell permeability, bioorthogonality, background labeling, and reaction efficiency, click reactions have already proven useful in a new generation of pulldown experiments (in which particular targets can be isolated using, for instance, reporter molecules which bind to a certain column), and fluorescence spectrometry (in which the fluorophore is attached to a target of interest and the target quantified or located). More recently, novel methods have been used to incorporate click reaction partners onto and into biomolecules, including the incorporation of unnatural amino acids containing reactive groups into proteins and the modification of nucleotides. These techniques represent a part of the field of chemical biology, in which click chemistry plays a fundamental role by intentionally and specifically coupling modular units to various ends.
The term "click chemistry" was coined by K. Barry Sharpless' wife, Jan Dueser, in 1998, and was first fully described by Sharpless, Hartmuth C. Kolb, and M.G. Finn of The Scripps Research Institute in 2001. In 2022, the Nobel Prize in Chemistry was jointly awarded to Carolyn R. Bertozzi, Morten P. Meldal and K. Barry Sharpless, "for the development of click chemistry and bioorthogonal chemistry". | 0 | Organic Chemistry |
In biochemistry, activation, specifically called bioactivation, is where enzymes or other biologically active molecules acquire the ability to perform their biological function, such as inactive proenzymes being converted into active enzymes that are able to catalyze their substrates reactions into products. Bioactivation may also refer to the process where inactive prodrugs are converted into their active metabolites, or the toxication' of protoxins into actual toxins.
An enzyme may be reversibly or irreversibly bioactivated. A major mechanism of irreversible bioactivation is where a piece of a protein is cut off by cleavage, producing an enzyme that will then stay active. A major mechanism of reversible bioactivation is substrate presentation where an enzyme translocates near its substrate. Another reversible reaction is where a cofactor binds to an enzyme, which then remains active while the cofactor is bound, and stops being active when the cofactor is removed.
In protein synthesis, amino acids are carried by transfer RNA (tRNA) molecules and added to a growing polypeptide chain on the ribosome. In order to transfer the amino acids to the ribosome, tRNAs must first be covalently bonded to the amino acid through their 3' CCA terminal. This binding is catalyzed by aminoacyl-tRNA synthetase, and requires a molecule of ATP. The amino acid bound to the tRNA is called an aminoacyl-tRNA, and is considered the activated molecule in protein translation. Once activated, the aminoacyl-tRNA may move to the ribosome and add the amino acid to the growing polypeptide chain. | 7 | Physical Chemistry |
In 2005 and again in 2011, the compound was prepared by total synthesis together with the unstrained compound riccardin C. In 2013, several other syntheses were reported for it and a racemic synthesis. | 0 | Organic Chemistry |
When used as an indicator in an EDTA titration, the characteristic blue end-point is reached when sufficient EDTA is added and the metal ions bound to the indicator are chelated by EDTA, leaving the free indicator molecule.
Eriochrome Black T has also been used to detect the presence of rare earth metals. | 3 | Analytical Chemistry |
The main function of glycolipids in the body is to serve as recognition sites for cell–cell interactions. The saccharide of the glycolipid will bind to a specific complementary carbohydrate or to a lectin (carbohydrate-binding protein), of a neighboring cell. The interaction of these cell surface markers is the basis of cell recognitions, and initiates cellular responses that contribute to activities such as regulation, growth, and apoptosis. | 0 | Organic Chemistry |
*France–Japan: TOULOUSE–NARA, Toulouse III - Paul Sabatier University. CEMES (CNRS) and Nara Institute of Science and Technology.
*United States–Austria: Rice–Graz nanoprix, Rice University and University of Graz
*Germany: GAZE, Technische Universitat Dresden
*United States: Ohio Bobcat Nanowagon, Ohio University
*France: StrasNanocar, University of Strasbourg and Strasbourg Institute of Material Physics and Chemistry (IPCMS)
*Spain: SAN SEBASTIAN, Donostia International Physics Center and University of Santiago de Compostela
*Japan: NIMS-MANA, National Institute for Materials Science (Tsukuba)
*Spain–Sweden: NANOHISPA, IMDEA Nanoscience Institute (University of Madrid) and Linköping University | 6 | Supramolecular Chemistry |
As discussed previously, the 4n rule mainly deals with clusters with electron counts of , in which approximately 4 electrons are on each vertex. As more electrons are added per vertex, the number of the electrons per vertex approaches 5. Rather than adopting structures based on deltahedra, the 5n-type clusters have structures based on a different series of polyhedra known as the 3-connected polyhedra, in which each vertex is connected to 3 other vertices. The 3-connected polyhedra are the duals of the deltahedra. The common types of 3-connected polyhedra are listed below.
The 5n rules are as follows.
Example: P
:Electron count: 4 × P = 4 × 5 = 20
:It is a 5n structure with n = 4, so it is tetrahedral
Example: PS
:Electron count 4 × P + 3 × S = 4 × 5 + 3 × 6 = 38
:It is a 5n + 3 structure with n = 7. Three vertices are inserted into edges
Example: PO
:Electron count 4 × P + 6 × O = 4 × 5 + 6 × 6 = 56
:It is a 5n + 6 structure with n = 10. Six vertices are inserted into edges | 7 | Physical Chemistry |
Phosphorus tribromide is a colourless liquid with the formula PBr. The liquid fumes in moist air due to hydrolysis and has a penetrating odour. It is used in the laboratory for the conversion of alcohols to alkyl bromides. | 0 | Organic Chemistry |
In optics, Lamberts cosine law says that the radiant intensity or luminous intensity observed from an ideal diffusely reflecting surface or ideal diffuse radiator is directly proportional to the cosine of the angle θ between the observers line of sight and the surface normal; . The law is also known as the cosine emission law or Lamberts emission law. It is named after Johann Heinrich Lambert, from his Photometria', published in 1760.
A surface which obeys Lamberts law is said to be Lambertian', and exhibits Lambertian reflectance. Such a surface has the same radiance/luminance when viewed from any angle. This means, for example, that to the human eye it has the same apparent brightness. It has the same radiance because, although the emitted power from a given area element is reduced by the cosine of the emission angle, the solid angle, subtended by surface visible to the viewer, is reduced by the very same amount. Because the ratio between power and solid angle is constant, radiance (power per unit solid angle per unit projected source area) stays the same. | 7 | Physical Chemistry |
The concept of a reversible reaction was introduced by Claude Louis Berthollet in 1803, after he had observed the formation of sodium carbonate crystals at the edge of a salt lake (one of the natron lakes in Egypt, in limestone):
:2NaCl + CaCO → NaCO + CaCl
He recognized this as the reverse of the familiar reaction
: NaCO + CaCl→ 2NaCl + CaCO
Until then, chemical reactions were thought to always proceed in one direction. Berthollet reasoned that the excess of salt in the lake helped push the "reverse" reaction towards the formation of sodium carbonate.
In 1864, Peter Waage and Cato Maximilian Guldberg formulated their law of mass action which quantified Berthollets observation. Between 1884 and 1888, Le Chatelier and Braun formulated Le Chateliers principle, which extended the same idea to a more general statement on the effects of factors other than concentration on the position of the equilibrium. | 7 | Physical Chemistry |
The term "representative layer" refers to a hypothetical plane parallel layer that has properties relevant to absorption spectroscopy that are representative of a sample as a whole. For particulate samples, a layer is representative if each type of particle in the sample makes up the same fraction of volume and surface area in the layer as in the sample. The void fraction in the layer is also the same as in the sample. Implicit in the representative layer theory is that absorption occurs at the molecular level, but that scatter is from a whole particle. | 7 | Physical Chemistry |
The paradigm of toxicological assessment of benzene is shifting towards the domain of molecular toxicology as it allows understanding of fundamental biological mechanisms in a better way. Glutathione seems to play an important role by protecting against benzene-induced DNA breaks and it is being identified as a new biomarker for exposure and effect. Benzene causes chromosomal aberrations in the peripheral blood leukocytes and bone marrow explaining the higher incidence of leukemia and multiple myeloma caused by chronic exposure. These aberrations can be monitored using fluorescent in situ hybridization (FISH) with DNA probes to assess the effects of benzene along with the hematological tests as markers of hematotoxicity. Benzene metabolism involves enzymes coded for by polymorphic genes. Studies have shown that genotype at these loci may influence susceptibility to the toxic effects of benzene exposure. Individuals carrying variant of NAD(P)H:quinone oxidoreductase 1 (NQO1), microsomal epoxide hydrolase (EPHX) and deletion of the glutathione S-transferase T1 (GSTT1) showed a greater frequency of DNA single-stranded breaks. | 2 | Environmental Chemistry |
In one of the earlier studies conducted by Manes, M., & Hofer, L. J. E., the Polyani theory was used to characterize liquid-phase adsorption isotherms on various concentrations activated carbon using a wide range of organic solvent. The polyani theory was shown to be a good fit for these various systems. Because of the results, the study introduced the possibility of predicting isotherms for similar systems using minimal data. However, the limitation is that the adsorption isotherms for a large variety of solvents can only fit over a limited range. The curve was not able to fit the data at high-capacity range. The study also concluded that there were a few anomalies in the results. The adsorption from carbon tetrachloride, cyclohexane, and carbon disulfide onto activated carbon was not able to fit well to the curve, and remain to be explained. The researchers who conducted the experiment speculate that steric effects of carbon tetrachloride and cyclohexane may have played a role. The study has been done with a variety of systems such as organic liquids from water solutions and organic solids from water solutions. | 7 | Physical Chemistry |
The expansive force of rusting, which may be called oxide jacking or rust burst, is a phenomenon that can cause damage to structures made of stone, masonry, concrete or ceramics, and reinforced with metal components. A definition is "the displacement of building elements due to the expansion of iron and steel products as the metal rusts and becomes iron oxide". Corrosion of other metals such as aluminum can also cause oxide jacking. | 8 | Metallurgy |
Spectral absorbance in frequency and spectral absorbance in wavelength of a material, denoted and respectively, are given by
where
* is the spectral radiant flux in frequency by that material;
* is the spectral radiant flux in frequency by that material;
* is the spectral transmittance in frequency of that material;
* is the spectral radiant flux in wavelength by that material;
* is the spectral radiant flux in wavelength by that material; and
* is the spectral transmittance in wavelength of that material.
Spectral absorbance is related to spectral optical depth by
where
* is the spectral optical depth in frequency, and
* is the spectral optical depth in wavelength.
Although absorbance is properly unitless, it is sometimes reported in "absorbance units", or AU. Many people, including scientific researchers, wrongly state the results from absorbance measurement experiments in terms of these made-up units. | 7 | Physical Chemistry |
While kinematical diffraction is adequate to understand the geometry of the diffraction spots, it does not correctly give the intensities and has a number of other limitations. For a more complete approach one has to include multiple scattering of the electrons using methods that date back to the early work of Hans Bethe in 1928. These are based around solutions of the Schrödinger equation using the relativistic effective mass described earlier. Even at very high energies dynamical diffraction is needed as the relativistic mass and wavelength partially cancel, so the role of the potential is larger than might be thought.
The main components of current dynamical diffraction of electrons include:
* Taking into account the scattering back into the incident beam both from diffracted beams and between all others, not just single scattering from the incident beam to diffracted beams. This is important even for samples which are only a few atoms thick.
* Modelling at least semi-empirically the role of inelastic scattering by an imaginary component of the potential, also called an "optical potential". There is always inelastic scattering, and often it can have a major effect on both the background and sometimes the details, see Figure 7 and 18.
* Higher-order numerical approaches to calculate the intensities such as multislice, matrix methods which are called Bloch-wave approaches or muffin-tin approaches. With these diffraction spots which are not present in kinematical theory can be present, e.g.
* Contributions to the diffraction from elastic strain and crystallographic defects, and also what Jens Lindhard called the string potential.
* For transmission electron microscopes effects due to variations in the thickness of the sample and the normal to the surface.
* Both in the geometry of scattering and calculations, for both LEED and RHEED, effects due to the presence of surface steps, surface reconstructions and other atoms at the surface. Often these change the diffraction details significantly.
* For LEED, use more careful analyses of the potential because contributions from exchange terms can be important. Without these the calculations may not be accurate enough. | 7 | Physical Chemistry |
Creatinine was first synthesized in vitro by Ivan Horbaczewski in 1885. One year later, Jaffes research was published in the paper Über den Niederschlag, welchen Pikrinsäre in normalem Harn erzeugt und über eine neue Reaction des Kreatinins. Jaffe had noticed that, when mixed in a sodium hydroxide (NaOH) solution, picric acid and creatinine formed a reddish-orange color and needle-like crystal precipitate. By using zinc chloride in a process known as the Neubauer reaction, and then performing the Weyls test, a colorimetric reaction using sodium nitroprusside (SNP), he determined that the precipitated compound was a double salt of the solution. Although he found the amount of precipitate directly proportional to the creatinine concentration, he also noted that the reaction was highly nonspecific and could be observed with many other organic compounds. | 1 | Biochemistry |
The lower heating value (LHV; net calorific value; NCV, or lower calorific value; LCV) is another measure of available thermal energy produced by a combustion of fuel, measured as a unit of energy per unit mass or volume of substance. In contrast to the HHV, the LHV considers energy losses such as the energy used to vaporize water - although its exact definition is not uniformly agreed upon. One definition is simply to subtract the heat of vaporization of the water from the higher heating value. This treats any HO formed as a vapor that is released as a waste. The energy required to vaporize the water is therefore lost.
LHV calculations assume that the water component of a combustion process is in vapor state at the end of combustion, as opposed to the higher heating value (HHV) (a.k.a. gross calorific value or gross CV) which assumes that all of the water in a combustion process is in a liquid state after a combustion process.
Another definition of the LHV is the amount of heat released when the products are cooled to . This means that the latent heat of vaporization of water and other reaction products is not recovered. It is useful in comparing fuels where condensation of the combustion products is impractical, or heat at a temperature below cannot be put to use.
One definition of lower heating value, adopted by the American Petroleum Institute (API), uses a reference temperature of .
Another definition, used by Gas Processors Suppliers Association (GPSA) and originally used by API (data collected for API research project 44), is the enthalpy of all combustion products minus the enthalpy of the fuel at the reference temperature (API research project 44 used 25 °C. GPSA currently uses 60 °F), minus the enthalpy of the stoichiometric oxygen (O) at the reference temperature, minus the heat of vaporization of the vapor content of the combustion products.
The definition in which the combustion products are all returned to the reference temperature is more easily calculated from the higher heating value than when using other definitions and will in fact give a slightly different answer. | 7 | Physical Chemistry |
The virial equation is especially useful to describe the causes of non-ideality at a molecular level (very few gases are mono-atomic) as it is derived directly from statistical mechanics:
Where the coefficients in the numerator are known as virial coefficients and are functions of temperature.
The virial coefficients account for interactions between successively larger groups of molecules. For example, accounts for interactions between pairs, for interactions between three gas molecules, and so on. Because interactions between large numbers of molecules are rare, the virial equation is usually truncated after the third term.
When this truncation is assumed, the compressibility factor is linked to the intermolecular-force potential φ by:
The Real gas article features more theoretical methods to compute compressibility factors. | 7 | Physical Chemistry |
The use of EAFs allows steel to be made from a 100% scrap metal feedstock. This greatly reduces the energy required to make steel when compared with primary steelmaking from ores.
Another benefit is flexibility: while blast furnaces cannot vary their production by much and can remain in operation for years at a time, EAFs can be rapidly started and stopped, allowing the steel mill to vary production according to demand.
Although steelmaking arc furnaces generally use scrap steel as their primary feedstock, if hot metal from a blast furnace or direct-reduced iron is available economically, these can also be used as furnace feed.
As EAFs require large amounts of electrical power, many companies schedule their operations to take advantage of off-peak electricity pricing.
A typical steelmaking arc furnace is the source of steel for a mini-mill, which may make bars or strip product. Mini-mills can be sited relatively near the markets for steel products, so the transport requirements are less than for an integrated mill, which would commonly be sited near a harbor for better access to shipping.
Electric arc furnace steelmaking results in lower carbon dioxide emissions of around 0.6 ton CO per ton of steel produced, which is significantly lower than the conventional production route via blast furnaces and the basic oxygen furnace. | 8 | Metallurgy |
Tim Requarth, reviewing The Vital Question for The New York Times, finds the book "seductive and often convincing, though speculation far outpaces evidence in many of the book’s passages. But perhaps for a biological theory of everything, that's to be expected, even welcomed."
Peter Forbes, reviewing The Vital Question in The Guardian, noted that the origin of life was once thought to be "safely consigned to wistful armchair musing", but that in the past 20 years new research in genomics, geology, biochemistry and molecular biology have transformed thinking in the field. "Here is the book that presents all this hard evidence and tightly interlocking theory to a wider audience.", writes Forbes.
Michael LePage, reviewing the book in New Scientist, writes that the fact that complex cells only evolved once is "very peculiar when you think about it", but it is just one of many large mysteries that Lane addresses, including aging and death, sex, and speciation. LePage finds Lane's arguments "powerful and persuasive", with many testable ideas. The book is not, he writes, the easiest to read, but "it does tell an incredible, epic story", from the dawn of life to the present day.
Caspar Henderson, in his book review in The Telegraph, writes that Lanes book "succeeds brilliantly" as good science writing can, expanding the readers horizons "in ways not previously imagined." Lane explains why the counterintuitive idea "that cross-membrane proton gradients power all living cells" is no mere technical detail: per gram, he notes, the power is 10,000 times denser than the sun, and it is conserved across every form of life, telling us something about how life began and how it was constrained to evolve. Henderson recommends the book as amazing and gripping, only criticising the publisher for the "pedestrian" quality of the design and printing.
The founder of Microsoft, Bill Gates, reviewed the book under the heading "This Biology Book Blew Me Away". It moved him to read two of Lanes other books, and to bring him to New York to interview him. Gates noted that "As much as I loved The Vital Question, its not for everyone. Some of the explanations are pretty technical. But this is a technical subject, and I doubt anyone else will make it much easier to understand without sacrificing crucial details."
Lane won the Michael Faraday Prize in 2016 for "excellence in communicating science to UK audiences". | 1 | Biochemistry |
The synthesis consists of three steps. In the first step, 2-iodobenzoic acid is oxidized by sodium periodate and cyclized to 1-hydroxy-1,2-benziodoxol-3(1H)-one. The target compound can then be obtained by acylation with acetic anhydride and subsequent substitution reaction with trifluoromethyltrimethylsilane.
Alternatively, trichloroisocyanuric acid can be used as oxidant in the place of sodium periodate for a newer one-pot synthesis method. | 0 | Organic Chemistry |
Yuri Alfredovich Berlin (, born Moscow, USSR, December 12, 1944) is an American physical chemist of Soviet origin. He is a research professor in the department of chemistry at Northwestern University. | 7 | Physical Chemistry |
Niludipine is a calcium channel blocker of the dihydropyridine class. It is a vasodilator that acts upon the coronary arteries of the heart-lung. It was found to produce a calcium antagonistic effect on the smooth muscle of hearts of canines and guinea pigs inhibiting myocardial oxidative metabolism. | 1 | Biochemistry |
Liquid-phase epitaxy (LPE) is a method to grow semiconductor crystal layers from the melt on solid substrates. This happens at temperatures well below the melting point of the deposited semiconductor. The semiconductor is dissolved in the melt of another material. At conditions that are close to the equilibrium between dissolution and deposition, the deposition of the semiconductor crystal on the substrate is relatively fast and uniform. The most used substrate is indium phosphide (InP). Other substrates like glass or ceramic can be applied for special applications. To facilitate nucleation, and to avoid tension in the grown layer the thermal expansion coefficient of substrate and grown layer should be similar.
Centrifugal liquid-phase epitaxy is used commercially to make thin layers of silicon, germanium, and gallium arsenide. Centrifugally formed film growth is a process used to form thin layers of materials by using a centrifuge. The process has been used to create silicon for thin-film solar cells and far-infrared photodetectors. Temperature and centrifuge spin rate are used to control layer growth. Centrifugal LPE has the capability to create dopant concentration gradients while the solution is held at constant temperature. | 3 | Analytical Chemistry |
Transcriptomic biomarkers analyze all RNA molecules, not solely the exome. Transcriptomic biomarkers reveal the molecular identity and concentration of RNA in a specific cell or population. Pattern-based RNA expression analysis provides increased diagnostic and prognostic capability in predicting therapeutic responses for individuals. For example, distinct RNA subtypes in breast cancer patients have different survival rates. | 1 | Biochemistry |
* H. J. M. Bowen, Trace Elements in Biochemistry. Academic Press, 1966.
* H. J. M. Bowen, Properties of Solids and their Structures. McGraw-Hill, 1967.
* H. J. M. Bowen, Environmental Chemistry of the Elements. Academic Press, 1979. . | 3 | Analytical Chemistry |
MLST is highly unambiguous and portable. Materials required for ST determination can be exchanged between laboratories. Primer sequences and protocols can be accessed electronically. It is reproducible and scalable. MLST is automated, combines advances in high throughput sequencing and bioinformatics with established population genetics techniques. MLST data can be used to investigate evolutionary relationships among bacteria. MLST provides good discriminatory power to differentiate isolates.
The application of MLST is huge, and provides a resource for the scientific, public health, and veterinary communities as well as the food industry. The following are examples of MLST applications. | 1 | Biochemistry |
Plants deficient in the IMMUTANS gene that encodes the oxidase are especially susceptible to photooxidative stress during early plastid development. The knockout plants exhibit a phenotype of variegated leaves with white patches that indicate a lack of pigmentation or photodamage. This effect is enhanced with increased light and temperature during plant development. The lack of plastid terminal oxidase indirectly causes photodamage during plastid development because protective carotenoids are not synthesized without the oxidase.
The enzyme is also thought to act as a safety valve for stress conditions in the photosynthetic apparatus. By providing an electron sink when the plastoquinone pool is over-reduced, the oxidase is thought to protect photosystem II from oxidative damage. Knockouts for Rubisco and photosystem II complexes, which would experience more photodamage than normal, exhibit an upregulation of plastid terminal oxidase. This effect is not universal because it requires plants to have additional PTOX regulation mechanisms. While many studies agree with the stress-protective role of the enzyme, one study showed that overexpression of PTOX increases the production of reactive oxygen species and causes more photodamage than normal. This finding suggests that an efficient antioxidant system is required for the oxidase to function as a safety valve for stress conditions and that it is more important during chloroplast biogenesis than in the regular functioning of the chloroplast. | 5 | Photochemistry |
Willard and his wife Margaret had two daughters, Ann and Nancy. Willard was a photography enthusiast and hobbyist who occasionally sold his work. He died in Ann Arbor, Michigan, on May 7, 1974. Michigan holds a named professorship in his honor; the current Willard Professor of Chemistry is Robert T. Kennedy. | 3 | Analytical Chemistry |
One structural consequence of acyclic systems due to the stereoelectronic effect is the gauche effect. In 1,2-difluoroethane, despite the steric clash, the preferred conformation is the gauche one because σ(C–H) is a good donor and σ*(C–F) is a good acceptor and the stereoelectronic effect (σ(C–H) → σ*(C–F)) requires the energy minimum to be gauche instead of anti.
This gauche effect and its impact on conformation are important in biochemistry. For example, in HIF-α subunit fragments containing (2S,4R)-4-hydroxyproline, the gauche interaction favors the conformer that can bind to the active site of pVHL. pVHL mediates the proteasomal degradation of HIF1A and with that the physiological response to hypoxia. | 4 | Stereochemistry |
The Lely method produces bulk silicon carbide crystals through the process of sublimation. Silicon carbide powder is loaded into a graphite crucible, which is purged with argon gas and heated to approximately . The silicon carbide near the outer walls of the crucible sublimes and is deposited on a graphite rod near the center of the crucible, which is at a lower temperature.
Several modified versions of the Lely process exist, most commonly the silicon carbide is heated from the bottom end rather than the walls of the crucible, and deposited on the lid. Other modifications include varying the temperature, temperature gradient, argon pressure, and geometry of the system. Typically, an induction furnace is used to achieve the required temperatures of . | 3 | Analytical Chemistry |
The emission spectrum of a chemical element or chemical compound is the spectrum of frequencies of electromagnetic radiation emitted due to electrons making a transition from a high energy state to a lower energy state. The photon energy of the emitted photons is equal to the energy difference between the two states. There are many possible electron transitions for each atom, and each transition has a specific energy difference. This collection of different transitions, leading to different radiated wavelengths, make up an emission spectrum. Each element's emission spectrum is unique. Therefore, spectroscopy can be used to identify elements in matter of unknown composition. Similarly, the emission spectra of molecules can be used in chemical analysis of substances. | 7 | Physical Chemistry |
The attack takes the form of a reaction between ammonia and copper to form the cuprammonium ion, formula [Cu(NH)], a chemical complex which is water-soluble, and hence washed from the growing cracks. The problem of cracking can therefore also occur in copper and any other copper alloy, such as bronze. The tendency of copper to react with ammonia was exploited in making rayon, and the deep blue colour of the aqueous solution of copper(II) oxide in ammonia is known as Schweizer's reagent. | 8 | Metallurgy |
Two binary solutions of different compositions or even two pure components can be mixed with various mixing ratios by masses, moles, or volumes.
The mass fraction of the resulting solution from mixing solutions with masses m and m and mass fractions w and w is given by:
where m can be simplified from numerator and denominator
and
is the mass mixing ratio of the two solutions.
By substituting the densities ρ(w) and considering equal volumes of different concentrations one gets:
Considering a volume mixing ratio r
The formula can be extended to more than two solutions with mass mixing ratios
to be mixed giving: | 3 | Analytical Chemistry |
In nerve terminals, synaptic vesicles are produced quickly to compensate for their rapid depletion during neurotransmitter release. Their biogenesis involves segregating synaptic vesicle membrane proteins from other cellular proteins and packaging those distinct proteins into vesicles of appropriate size. Besides, it entails the endocytosis of synaptic vesicle membrane proteins from the plasma membrane.
Synaptoblastic and synaptoclastic refer to synapse-producing and synapse-removing activities within the biochemical signalling chain. This terminology is associated with the Bredesen Protocol for treating Alzheimers disease, which conceptualizes Alzheimers as an imbalance between these processes. As of October 2023, studies concerning this protocol remain small and few results have been obtained within a standardized control framework. | 1 | Biochemistry |
Neurophysins are carrier proteins which transport the hormones oxytocin and vasopressin to the posterior pituitary from the paraventricular and supraoptic nucleus of the hypothalamus, respectively. Inside the neurosecretory granules, the analogous neurophysin I and II form stabilizing complexes via covalent interactions. Stabilizing neurophysin-hormone complexes that are formed within neurosecretory granules located in the posterior pituitary gland aid in intra-axonal transport. During intra-axonal transport, the neurophysin's are believed to prevent the bound hormone from leaking into the cytoplasmic space and proteolytic digestion via enzymes. However, due to the low concentration of neurophysin in the blood, it is likely the protein-hormone complex dissociates, indicating the neurophysin does not aid in transporting the hormone through the circulatory system.
Neurophysins are also secreted out of the posterior pituitary hypothalamus, each carrying their respective associated passenger hormone. When the posterior pituitary hypothalamus secretes vasopressin and its neurophysin carrier, it also secretes a glycopeptide.
There are two types:
* Neurophysin I - Oxytocin
* Neurophysin II - Vasopressin (Also known as "antidiuretic hormone" or ADH) | 1 | Biochemistry |
The safety profile of HMB in adult humans is based upon evidence from clinical trials in humans and animal studies. In humans, no adverse effects in young adults or older adults have been reported when HMB is taken in doses of 3 grams per day for up to a year. Studies on young adults taking 6 grams of HMB per day for up to 2 months have also reported no adverse effects. Studies with supplemental HMB on young, growing rats and livestock have reported no adverse effects based upon clinical chemistry or observable characteristics; for humans younger than 18, there is limited data on the safety of supplemental HMB. The human equivalent dose of HMB for the no-observed-adverse-effect level (NOAEL) that was identified in a rat model is approximately 0.4 g/kg of body weight per day.
Two animal studies have examined the effects of HMB supplementation in pregnant pigs on the offspring and reported no adverse effects on the fetus. No clinical testing with supplemental HMB has been conducted on pregnant women, and pregnant and lactating women are advised not to take HMB by Metabolic Technologies, Inc., the company that grants licenses to include HMB in dietary supplements, due to a lack of safety studies. | 1 | Biochemistry |
The reddish color typical of tholins is characteristic of many Trans-Neptunian objects, including plutinos in the outer Solar System such as 28978 Ixion. Spectral reflectances of Centaurs also suggest the presence of tholins on their surfaces. The New Horizons exploration of the classical Kuiper belt object 486958 Arrokoth revealed reddish color at its surface, suggestive of tholins. | 9 | Geochemistry |
Using conventional FT technology the process ranges in carbon efficiency from 25 to 50 percent and a thermal efficiency of about 50% for CTL facilities idealised at 60% with GTL facilities at about 60% efficiency idealised to 80% efficiency. | 0 | Organic Chemistry |
Many bacteria use the anaerobic pathway for synthesizing unsaturated fatty acids. This pathway does not utilize oxygen and is dependent on enzymes to insert the double bond before elongation utilizing the normal fatty acid synthesis machinery. In Escherichia coli, this pathway is well understood.
* FabA is a β-hydroxydecanoyl-ACP dehydrase – it is specific for the 10-carbon saturated fatty acid synthesis intermediate (β-hydroxydecanoyl-ACP).
* FabA catalyzes the dehydration of β-hydroxydecanoyl-ACP, causing the release of water and insertion of the double bond between C7 and C8 counting from the methyl end. This creates the trans-2-decenoyl intermediate.
* Either the trans-2-decenoyl intermediate can be shunted to the normal saturated fatty acid synthesis pathway by FabB, where the double bond will be hydrolyzed and the final product will be a saturated fatty acid, or FabA will catalyze the isomerization into the cis-3-decenoyl intermediate.
* FabB is a β-ketoacyl-ACP synthase that elongates and channels intermediates into the mainstream fatty acid synthesis pathway. When FabB reacts with the cis-decenoyl intermediate, the final product after elongation will be an unsaturated fatty acid.
* The two main unsaturated fatty acids made are Palmitoleoyl-ACP (16:1ω7) and cis-vaccenoyl-ACP (18:1ω7).
Most bacteria that undergo anaerobic desaturation contain homologues of FabA and FabB. Clostridia are the main exception; they have a novel enzyme, yet to be identified, that catalyzes the formation of the cis double bond.
;Regulation
This pathway undergoes transcriptional regulation by FadR and FabR. FadR is the more extensively studied protein and has been attributed bifunctional characteristics. It acts as an activator of fabA and fabB transcription and as a repressor for the β-oxidation regulon. In contrast, FabR acts as a repressor for the transcription of fabA and fabB. | 1 | Biochemistry |
Esters react with strong oxidizing acids, which may cause a violent reaction that is sufficiently exothermic to ignite the esters and the reaction products. Heat is also generated by the interaction of esters with alkali solutions. Very flammable hydrogen gas is generated by mixing esters with alkali metals and ionic hydrides. | 0 | Organic Chemistry |
Bacteria utilize complex long helical proteins as chemoreceptors, permitting signals to travel long distances across the cell's membrane. Chemoreceptors allow bacteria to react to chemical stimuli in their environment and regulate their movement accordingly. In archaea, transmembrane receptors comprise only 57% of chemoreceptors, while in bacteria the percentage rises to 87%. This is an indicator that chemoreceptors play a heightened role in the sensing of cytosolic signals in archaea. | 3 | Analytical Chemistry |
Mutations to coactivator genes leading to loss or gain of protein function have been linked to diseases and disorders such as birth defects, cancer (especially hormone dependent cancers), neurodevelopmental disorders and intellectual disability (ID), among many others. Dysregulation leading to the over- or under-expression of coactivators can detrimentally interact with many drugs (especially anti-hormone drugs) and has been implicated in cancer, fertility issues and neurodevelopmental and neuropsychiatric disorders. For a specific example, dysregulation of CREB-binding protein (CBP)—which acts as a coactivator for numerous transcription factors within the central nervous system (CNS), reproductive system, thymus and kidneys—has been linked to Huntington's disease, leukaemia, Rubinstein-Taybi syndrome, neurodevelopmental disorders and deficits of the immune system, hematopoiesis and skeletal muscle function. | 1 | Biochemistry |
The Zeisel determination or Zeisel test is a chemical test for the presence of esters or ethers in a chemical substance. It is named after the Czech chemist Simon Zeisel (1854–1933). In a qualitative test a sample is first reacted with a mixture of acetic acid and hydrogen iodide in a test tube. The ensuing reaction results in the cleavage of the ether or the ester into an alkyl iodide and respectively an alcohol or a carboxylic acid.
By heating this mixture, the gases are allowed to come into contact with a piece of paper higher up the test tube saturated with silver nitrate. Any alkyl iodide present will give a reaction with the silver compound to silver iodide which has a red or yellow color. By filtering and weighing this precipitate it is possible to quantitatively calculate the number of iodine atoms and hence alkoxy groups. For example, prior to the development of the more precise methods of NMR spectroscopy and mass spectrometry, the Zeisel test was widely used to determine the number of methoxy (-OCH) and ethoxy (-OCHCH) groups in carbohydrate and organophosphorus insecticides.
An alternative qualitative Zeisel test can be done with the use of mercury(II) nitrate instead of silver nitrate, leading to the formation of scarlet red mercury(II) iodide.
Synthetic applications: | 3 | Analytical Chemistry |
Common organosulfur compounds present in petroleum fractions at the level of 200–500 ppm. Common compounds are thiophenes, especially dibenzothiophenes. By the process of hydrodesulfurization (HDS) in refineries, these compounds are removed as illustrated by the hydrogenolysis of thiophene: | 9 | Geochemistry |
Sea salt aerosol, which originally comes from sea spray, is one of the most widely distributed natural aerosols. Sea salt aerosols are characterized as non-light-absorbing, highly hygroscopic, and having coarse particle size. Some sea salt dominated aerosols could have a single scattering albedo as large as ~0.97. Due to the hygroscopy, a sea salt particle can serve as a very efficient cloud condensation nuclei (CCN), altering cloud reflectivity, lifetime, and precipitation process. According to the IPCC report, the total sea salt flux from ocean to atmosphere is ~3300 teragrams (Tg) per year. | 9 | Geochemistry |
Hydrides containing deuterium are known as deuterides. Some deuterides, such as LiD, are important fusion fuels in thermonuclear weapons and useful moderators in nuclear reactors. | 0 | Organic Chemistry |
Cer6 is a LTR retrotransposon that is described from sequencing data in the chromosome III of C. elegans. | 1 | Biochemistry |
Allyl boronic esters engage in electrophilic allyl shifts very much like silicon pendant in the Sakurai reaction. In one study a diallylation reagent combines both: | 0 | Organic Chemistry |
Carcinogenic cells undergo a metabolic rewiring during oncogenesis, and oncometabolites play an important role. In cancer, there are several reprogrammed metabolic pathways that help cells survive when nutrients are scarce: Aerobic glycolysis, an increase in glycolytic flux, also known as the Warburg effect, allows glycolytic intermediates to supply subsidiary pathways to meet the metabolic demands of proliferating tumorigenic cells. Another studied reprogrammed pathway is gain of function of the oncogene MYC. This gene encodes a transcription factor that boosts the expression of a number of genes involved in anabolic growth via mitochondrial metabolism. Oncometabolite production is another example of metabolic deregulation. | 1 | Biochemistry |
Many compounds from first row of transition metal monoxides (MO), from TiO to NiO, have a rocksalt structure. The rock salt structure is generated by filling all octahedral sites with cations in an oxygen anion fcc array. | 7 | Physical Chemistry |
Soluble cell adhesion molecules (sCAMs) are a class of
cell adhesion molecule (CAMs - cell surface binding proteins) that may represent important biomarkers for inflammatory processes involving activation or damage to cells such as platelets and the endothelium.
They include soluble isoforms of the cell adhesion molecules ICAM-1, VCAM-1, E-selectin and P-selectin (distinguished as sICAM-1, sVCAM-1, sE-selectin and sP-selectin). The cellular expression of CAMs is difficult to assess clinically, but these soluble forms are present in the circulation and may serve as markers for CAMs.
Research has focused on their role in cardiovascular (particularly atherosclerosis), connective tissue and neoplastic diseases, where blood plasma levels may be a marker of the disease severity or prognosis, and they may be useful in evaluating progress of some treatments.
Many studies have postulated that increased production of cell adhesion molecules (CAMs) on the vascular endothelium (blood vessel lining) plays a role in the development of arterial plaque, with the suggestion from both in vitro and in vivo studies that the CAM production is increased by dyslipidemia (abnormal lipid levels in the blood).
Research studies have used sCAMs as biomarkers to measure correlations with nutrients or nutrient levels as significant, or not. | 1 | Biochemistry |
DNA supercoiling refers to the amount of twist in a particular DNA strand, which determines the amount of strain on it. A given strand may be "positively supercoiled" or "negatively supercoiled" (more or less tightly wound). The amount of a strand's supercoiling affects a number of biological processes, such as compacting DNA and regulating access to the genetic code (which strongly affects DNA metabolism and possibly gene expression). Certain enzymes, such as topoisomerases, change the amount of DNA supercoiling to facilitate functions such as DNA replication and transcription. The amount of supercoiling in a given strand is described by a mathematical formula that compares it to a reference state known as "relaxed B-form" DNA. | 1 | Biochemistry |
Ionochromic materials exist in a wide range of molecules, including organic molecules, pH-sensitive dyes and indicators, and other color-changing compounds with chromophores. Some of these molecules include phthalides, fluorans, and leucotriarylmethanes. | 3 | Analytical Chemistry |
Plants in the genus Humulus and Cannabis produce terpenophenolic metabolites, compounds that are meroterpenes. Phenolic lipids are long aliphatic chains bonded to a phenolic moiety. | 0 | Organic Chemistry |
Because of the diffraction limit in the resolution of conventional lens-based microscopes, namely D = 0.61λ/nsinθ, the maximum resolution obtainable with an optical microscope is ~200 nm. A new type of lens using multiple scattering of light allowed to improve the resolution to about 100 nm. Several new microscopy techniques with a sub-nanometer resolution have been developed in the last several decades, such as electron microscopy (SEM and TEM) and scanning probe microscopy (NSOM, STM and AFM). SPM differs from other techniques in that the excitation and signal collection are very close (less than diffraction limit distance) to the sample. Instead of using a conventional lens to obtain magnified images of samples, an SPM scans across the sample with a very sharp probe. Whereas SEM and TEM usually require vacuum and an extensive sample preparation, SPM measurements can be performed in atmospheric or liquid conditions.
Despite the achievable resolution of atomic scale for AFM and NSOM techniques, it does not provide chemical information of the sample. The infrared part of the electromagnetic spectrum covers molecular vibrations which can characterize chemical bonding within the sample.
By combining SPM and vibrational spectroscopy, AFM/IR-NSOM and AFM-IR have emerged as useful characterization tools that integrate the high spatial resolution abilities of AFM with IR spectroscopy. This new technique can be referred to as AFM-FTIR, AFM-IR and NSOM/FTIR. AFM and NSOM can be used to detect the response when a modulated infrared radiation generated by an FTIR spectrometer is absorbed by a material. In the AFM-IR technique the absorption of the radiation by sample will cause a rapid thermal expansion wave which will be transferred to the vibrational modes of the AFM cantilever. Specifically, thermal expansion wave induces a vertical displacement of the ATM tip (Figure 6). A local IR absorption spectrum then can be obtained through the measurement of the amplitude of the cantilever, which is a function of the IR source wavelength. For example, when the radiation laser wavelength is tuned at the resonance frequency with the vibrational absorption frequency of the sample, the displacement intensity of the cantilever will increase until the laser wavelength reaches the maximum of sample absorption. The displacement of the cantilever will then be reduced as the laser wavelength is tuned past the absorption maximum. This approach can map chemical composition beyond the diffraction-limit resolution and can also provide three-dimensional topographic, thermal and mechanical information at the nanoscale. Overall, it overcomes the resolution limit of traditional IR spectroscopy and adds chemical and mechanical mapping to the AFM and NSOM. | 7 | Physical Chemistry |
Highly crosslinked resins typically swell much less than the latter. The property that allows these types of resins to work efficiently lies in their porous properties. The reacting compound can diffuse through the porous layer of the resin to converge with the scavenger's functional group. These types of resins are utilized in situations where swelling of the resins may cause a physical barrier to reaction purification. Contain much higher content of divinylbenzene. | 0 | Organic Chemistry |
The production of the cannabinoids THC and CBD are a result of a series of chemical reactions, and are just two types of over a hundred that are known. Inside the transcriptomes of glandular trichomes in the cannabis plant, the pathway for cannabinoid production takes place. Beginning with the formation of 3,5,7-trioxododecaneoyl-COA by the condensation reaction between hexanoyl-CoA and malonyl-CoA, catalyzed by type III polyketide synthase (PKS), the product is then used to form olivetolic acid. After the geranylation of olivetolic acid, cannabigerolic acid (CBGA) or cannabigerivarinic acid (CBGVA) is formed. The decarboxylation of these acids yield what we recognize as THC and CBD. | 1 | Biochemistry |
Gram-positive bacteria use autoinducing peptides (AIP) as their autoinducers.
When gram-positive bacteria detect high concentration of AIPs in their environment, that happens by way of AIPs binding to a receptor to activate a kinase. The kinase phosphorylates a transcription factor, which regulates gene transcription. This is called a two-component system.
Another possible mechanism is that AIP is transported into the cytosol, and binds directly to a transcription factor to initiate or inhibit transcription. | 1 | Biochemistry |
A thermodynamic system consisting of a single phase in the absence of external forces, in its own internal thermodynamic equilibrium, is homogeneous. This means that the material in any small volume element of the system can be interchanged with the material of any other geometrically congruent volume element of the system, and the effect is to leave the system thermodynamically unchanged. In general, a strong external force field makes a system of a single phase in its own internal thermodynamic equilibrium inhomogeneous with respect to some intensive variables. For example, a relatively dense component of a mixture can be concentrated by centrifugation. | 7 | Physical Chemistry |
The Hometrees (Kelutral in Navi) are great enough to house hundreds of clan members. The trees are honeycombed with natural hollows and alcoves in which the Navi sleep, eat, weave, dance, and celebrate their connection to Eywa. Adult Hometrees are more than tall, and roughly in diameter. The Omaticaya inhabit a Giant Hometree, standing roughly tall. A distinguishable feature of the movie landscape, the tree itself is central to the movie story arc. Like many sacred sites on Pandora, the Giant Hometree sits above a large deposit of unobtanium. It is destroyed by the humans using rockets and missiles, which leads to the Navi clans alliance against the humans. | 1 | Biochemistry |
The synthesis of pyrethrin I involves the esterification of (+)-trans-chrysanthemic acid with (S)-(Z)-pyrethrolone. One synthetic method for each of these is shown in the images below. Sobti and Dev of the Malti-Chem Research Centre in Nadesari, vadodara, India published this method for chrysanthemic acid in 1974. The starting material for the synthesis uses commercially available (+)-3α, 4α-epoxycarane (1). A lactone is eventually formed and the ring is opened by the use of a Grignard reagent to give (+)-trans-chrysanthemic acid. The preparation of (S)-pyrethrolone is essentially a 2 step synthesis. The starting material (S)-4-hydroxy-3-methyl-2-(2-propynyl)-2-cyclopenten-1-one (7) is also commercially available as the alcohol moiety of ETOC. Tetrakis(triphenylphosphine)palladium(0), copper(I) iodide, triethylamine, and vinyl bromide are added to (7) to add two more carbons and form (8). The final step is the addition of an activated zinc compound to reduce the triple carbon bond to form the cis product, (S)-pyrethrolone (9). Although no journal articles specify the combining of the alcohol and acid moieties of pyrethrin I, they could be combined through an esterification process to form the wanted product. | 0 | Organic Chemistry |
1,2,4,5-Tetrachloro-3-nitrobenzene (tecnazene) is an organic compound with the formula . It is a colorless solid. A related isomer is 1,2,3,4-tetrachloro-5-nitrobenzene.
It is used as a standard for quantitative analysis by nuclear magnetic resonance.
1,2,4,5-Tetrachloro-3-nitrobenzene is also a fungicide used to prevent dry rot and sprouting on potatoes during storage. | 3 | Analytical Chemistry |
Ferrocene is a redox-active organometallic compound which can be incorporated into various monomers and used to make polymers which can be tethered onto a surface. Vinylferrocene (ferroceneylethene) can be prepared by a Wittig reaction and then polymerized to form polyvinylferrocene (PVFc), an analog of polystyrene. Another polymer which can be formed is poly( ferrocenecarboxylate), PFcMA. Both PVFc and PFcMA have been tethered onto silica wafers and the wettability measured when the polymer chains are uncharged and when the ferrocene moieties are oxidised to produce positively charged groups, as illustrated at right. The contact angle with water on the PFcMA-coated wafers was 70° smaller following oxidation, while in the case of PVFc the decrease was 30°, and the switching of wettability has been shown to be reversible. In the PFcMA case, the effect of longer chains with more ferrocene groups (and also greater molar mass) has been investigated, and it was found that longer chains produce significantly larger contact angle reductions. | 7 | Physical Chemistry |
Conventional measurement of the EQE will give the efficiency of the overall device. However it is often useful to have a map of the EQE over large area of the device. This mapping provides an efficient way to visualize the homogeneity and/or the defects in the sample. It was realized by researchers from the Institute of Researcher and Development on Photovoltaic Energy (IRDEP) who calculated the EQE mapping from electroluminescence measurements taken with a hyperspectral imager. | 7 | Physical Chemistry |
In 1965, a paper was published by two researchers of the Scientific Laboratory at the Ford Motor Company, P. D. Maker and R. W. Terhune, in which the CARS phenomenon was reported for the first time. Maker and Terhune used a pulsed ruby laser to investigate the third order response of several materials. They first passed the ruby beam of frequency ω through a Raman shifter to create a second beam at ω-ω, and then directed the two beams simultaneously onto the sample. When the pulses from both beams overlapped in space and time, the Ford researchers observed a signal at ω+ω, which is the blue-shifted CARS signal. They also demonstrated that the signal increases significantly when the difference frequency ω between the incident beams matches a Raman frequency of the sample. Maker and Terhune called their technique simply three wave mixing experiments. The name coherent anti-Stokes Raman spectroscopy was assigned almost ten years later, by Begley et al. at Stanford University in 1974. Since then, this vibrationally sensitive nonlinear optical technique has been commonly known as CARS. | 3 | Analytical Chemistry |
Joseph H. Burckhalter was a chemist who worked in the field of isothiocyanate compounds. In 1995 he was inducted into the National Inventors Hall of Fame. Burckhalter is also a member of the Medicinal Chemistry Hall of Fame.
Burckhalter earned a B.S. in chemistry from the University of South Carolina in 1934 and an M.S. in organic chemistry from the University of Illinois, Urbana, in 1938. In 1942, he received his doctorate in medicinal chemistry at the University of Michigan, where he had been a graduate student of Frederick Blicke. | 0 | Organic Chemistry |
The types of RNAs transcribed from RNA polymerase III include:
*Transfer RNAs
*5S ribosomal RNA
*U6 spliceosomal RNA
*RNase P and RNase MRP RNA
*7SL RNA (the RNA component of the signal recognition particle)
*Vault RNAs
*Y RNA
*SINEs (short interspersed repetitive elements)
*7SK RNA
*Several microRNAs
*Several small nucleolar RNAs
*Several gene regulatory antisense RNAs | 1 | Biochemistry |
Membrane-introduction mass spectrometry (MIMS) is a method of introducing analytes into the mass spectrometer's vacuum chamber via a semi-permeable membrane. Usually a thin, gas-permeable, hydrophobic membrane is used, for example polydimethylsiloxane. Samples can be almost any fluid including water, air or sometimes even solvents. The great advantage of the method of sample introduction is its simplicity. MIMS can be used to measure a variety of analytes in real-time, with little or no sample preparation. MIMS is most useful for the measurement of small, non-polar molecules, since molecules of this type have a greater affinity for the membrane material than the sample. The advantage of this method is that complex samples that cannot diffuse through the membrane are not incorporated into the mass spectroscopic measurements, highlighting the simplicity of only analyzing (small) molecules of interest. | 3 | Analytical Chemistry |
The main application for air filters are combustion air to engines. The filter papers are transformed into filter cartridges, which then is fitted to a holder. The construction of the cartridges mostly requires that the paper is stiff enough to be self-supporting. A paper for air filters needs to be very porous and have a weight of 100–200 g/m. Normally particularly long fibrous pulp that is mercerised is used to get these properties. The paper is normally impregnated to improve the resistance to moisture. Some heavy duty qualities are made to be rinsed and thereby extend the life of the filter. | 3 | Analytical Chemistry |
Operons occur primarily in prokaryotes but also rarely in some eukaryotes, including nematodes such as C. elegans and the fruit fly, Drosophila melanogaster. rRNA genes often exist in operons that have been found in a range of eukaryotes including chordates. An operon is made up of several structural genes arranged under a common promoter and regulated by a common operator. It is defined as a set of adjacent structural genes, plus the adjacent regulatory signals that affect transcription of the structural genes. The regulators of a given operon, including repressors, corepressors, and activators, are not necessarily coded for by that operon. The location and condition of the regulators, promoter, operator and structural DNA sequences can determine the effects of common mutations.
Operons are related to regulons, stimulons and modulons; whereas operons contain a set of genes regulated by the same operator, regulons contain a set of genes under regulation by a single regulatory protein, and stimulons contain a set of genes under regulation by a single cell stimulus. According to its authors, the term "operon" is derived from the verb "to operate". | 1 | Biochemistry |
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