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Another form of plant communication occurs through their root networks. Through roots, plants can share many different resources including carbon, nitrogen, and other nutrients. This transfer of below ground carbon is examined in Philip et al. 2011. The goals of this paper were to test if carbon transfer was bi-directional, if one species had a net gain in carbon, and if more carbon was transferred through the soil pathway or common mycorrhizal network (CMN). CMNs occur when fungal mycelia link roots of plants together. The researchers followed seedlings of paper birch and Douglas-fir in a greenhouse for 8 months, where hyphal linkages that crossed their roots were either severed or left intact. The experiment measured amounts of labeled carbon exchanged between seedlings. It was discovered that there was indeed a bi-directional sharing of carbon between the two tree species, with the Douglas-fir receiving a slight net gain in carbon. Also, the carbon was transferred through both soil and the CMN pathways, as transfer occurred when the CMN linkages were interrupted, but much more transfer occurred when the CMN's were left unbroken.
This experiment showed that through fungal mycelia linkage of the roots of two plants, plants are able to communicate with one another and transfer nutrients as well as other resources through below ground root networks. Further studies go on to argue that this underground “tree talk” is crucial in the adaptation of forest ecosystems. Plant genotypes have shown that mycorrhizal fungal traits are heritable and play a role in plant behavior. These relationships with fungal networks can be mutualistic, commensal, or even parasitic. It has been shown that plants can rapidly change behavior such as root growth, shoot growth, photosynthetic rate, and defense mechanisms in response to mycorrhizal colonization. Through root systems and common mycorrhizal networks, plants are able to communicate with one another below ground and alter behaviors or even share nutrients depending on different environmental cues. | 1 | Biochemistry |
James Beaumont Neilson, previously foreman at Glasgow gas works, invented the system of preheating the blast for a furnace. He found that by increasing the temperature of the incoming air to 300 degrees Fahrenheit, he could reduce the fuel consumption from 8.06 tons of coal to 5.16 tons of coal per ton of produced iron with further reductions at even higher temperatures. He, with partners including Charles Macintosh, patented this in 1828. Initially the heating vessel was made of wrought iron plates, but these oxidized, and he substituted a cast iron vessel.
On the basis of a January 1828 patent, Thomas Botfield has a historical claim as the inventor of the hot blast method. Neilson is credited as inventor of hot blast, because he won patent litigation. Neilson and his partners engaged in substantial litigation to enforce the patent against infringers. The spread of this technology across Britain was relatively slow. By 1840, 58 ironmasters had taken out licenses, yielding a royalty income of £30,000 per year. By the time the patent expired there were 80 licenses. In 1843, just after it expired, 42 of the 80 furnaces in south Staffordshire were using hot blast, and uptake in south Wales was even slower.
Other advantages of hot blast were that raw coal could be used instead of coke. In Scotland, the relatively poor "black band" ironstone could be profitably smelted. It also increased the daily output of furnaces. In the case of Calder ironworks from 5.6 tons per day in 1828 to 8.2 in 1833, which made Scotland the lowest cost steel producing region in Britain in the 1830s.
Early hot blast stoves were troublesome, as thermal expansion and contraction could cause breakage of pipes. This was somewhat remedied by supporting the pipes on rollers. It was also necessary to devise new methods of connecting the blast pipes to the tuyeres, as leather could no longer be used.
Ultimately this principle was applied even more efficiently in regenerative heat exchangers, such as the Cowper stove (which preheat incoming blast air with waste heat from flue gas; these are used in modern blast furnaces), and in the open hearth furnace (for making steel) by the Siemens-Martin process.
Independently, George Crane and David Thomas, of the Yniscedwyn Works in Wales, conceived of the same idea, and Crane filed for a British patent in 1836. They began producing iron by the new process on February 5, 1837. Crane subsequently bought Gessenhainer's patent and patented additions to it, controlling the use of the process in both Britain and the US. While Crane remained in Wales, Thomas moved to the US on behalf of the Lehigh Coal & Navigation Company and founded the Lehigh Crane Iron Company to utilize the process. | 8 | Metallurgy |
Taste is a form of chemoreception that takes place in the specialised taste receptors, contained in structures called taste buds in the mouth. Taste buds are mainly on the upper surface (dorsum) of the tongue. The function of taste perception is vital to help prevent harmful or rotten foods from being consumed. There are also taste buds on the epiglottis and upper part of the esophagus. The taste buds are innervated by a branch of the facial nerve the chorda tympani, and the glossopharyngeal nerve. Taste messages are sent via these cranial nerves to the brain. The brain can distinguish between the chemical qualities of the food. The five basic tastes are referred to as those of saltiness, sourness, bitterness, sweetness, and umami. The detection of saltiness and sourness enables the control of salt and acid balance. The detection of bitterness warns of poisons—many of a plant's defences are of poisonous compounds that are bitter. Sweetness guides to those foods that will supply energy; the initial breakdown of the energy-giving carbohydrates by salivary amylase creates the taste of sweetness since simple sugars are the first result. The taste of umami is thought to signal protein-rich food. Sour tastes are acidic which is often found in bad food. The brain has to decide very quickly whether the food should be eaten or not. It was the findings in 1991, describing the first olfactory receptors that helped to prompt the research into taste. The olfactory receptors are located on cell surfaces in the nose which bind to chemicals enabling the detection of smells. It is assumed that signals from taste receptors work together with those from the nose, to form an idea of complex food flavours. | 1 | Biochemistry |
There are different ways to derive the summation theorems. One is analytical and rigorous using a combination of linear algebra and calculus. The other is less rigorous, but more operational and intuitive. The latter derivation is shown here.
Consider the two-step pathway:
where and are fixed species so that the system can achieve a steady-state.
Let the pathway be at steady-state and imagine increasing the concentration of enzyme, , catalyzing the first step, , by an amount, . The effect of this is to increase the steady-state levels of S and flux, J. Let us now increase the level of by such that the change in S is restored to the original value it had at steady-state.
The net effect of these two changes is by definition, .
There are two ways to look at this thought experiment, from the perspective of the system and from the perspective of local changes. For the system we can compute the overall change in flux or species concentration by adding the two control coefficient terms, thus:
We can also look at what is happening locally at every reaction step for which there will be two: one for , and another for . Since the thought experiment guarantees that , the local equations are quite simple:
where the terms are the elasticities. However, because the enzyme elasticity is equal to one, these reduce to:
Because the pathway is linear, at steady-state, . We can substitute these expressions into the system equations to give:
Note that at steady state the change in and must be the same, therefore .
Setting , we can rewrite the above equations as:
We then conclude through cancelation of since , that: | 1 | Biochemistry |
In physics, zilch (or zilches) is a set of ten conserved quantities of the source-free electromagnetic field, which were discovered by Daniel M. Lipkin in 1964. The name refers to the fact that the zilches are only conserved in regions free of electric charge, and therefore have limited physical significance. One of the conserved quantities (Lipkin' ) has an intuitive physical interpretation and is also known as optical chirality.
In particular, first, Lipkin observed that if he defined the quantities | 4 | Stereochemistry |
Adverse effects are similar to oxcarbazepine. The most common ones (more than 10% of patients) are tiredness and dizziness. Other fairly common side effects (1 to 10%) include impaired coordination, gastrointestinal disorders such as diarrhoea, nausea and vomiting, rash (1.1%), and hyponatremia (low sodium blood levels, 1.2%). There may also be an increased risk of suicidal thoughts. | 4 | Stereochemistry |
Adhesive strength depends also on the size and macroscopic shape of adhesive contact. When a rigid punch with a flat but oddly shaped face is carefully pulled off its soft counterpart, the detachment does not occur instantaneously. Instead, detachment fronts start at pointed corners and travel inwards until the final configuration is reached. The main parameter determining the adhesive strength of flat contacts appears to be the maximum linear size of the contact. The process of detachment can as observed experimentally can be seen in the film. | 6 | Supramolecular Chemistry |
Titanium and titanium alloys have been wide usage in aerospace, medical, and maritime applications. The most known titanium alloy that adopts solid solution strengthening is Ti-6Al-4V. Also, the addition of oxygen to pure Ti alloy adopts a solid solution strengthening as a mechanism to the material, while adding it to Ti-6Al-4V alloy doesn’t have the same influence. | 8 | Metallurgy |
In 1955, S. Winstein and T. G. Traylor published a study of the mechanism of acetolysis of organomercury compounds. They propose a series of possible mechanisms for the process, which they rule out through based on their kinetic data. A concerted metalation deprotonation is considered, and they are unable to rule it out through the data they collect.
The metalation of organic C–H bonds was extended from mercury to palladium in 1968 by J. M. Davidson and C. Triggs who identified that palladium acetate reacts with benzene in perchloric acid and acetic acid to give biphenyl, palladium(0), and 2 equivalents of acetic acid through an organopalladium intermediate. Early mechanistic studies found that palladium acetate was the best palladium precatalyst due to the presence of the acetate ligand. Mechanistic investigation has been ongoing since these initial discoveries, and infrared spectroscopy on the picosecond–millisecond time scale was used in 2021 to observe the states involved in proton transfer from acetic acid to a metalated ligand, which is the microscopic reverse of a concerted metalation deprotonation process. | 0 | Organic Chemistry |
a. Fructose is not the only sugar found in fruits. Glucose and sucrose are also found in varying quantities in various fruits, and sometimes exceed the fructose present. For example, 32% of the edible portion of a date is glucose, compared with 24% fructose and 8% sucrose. However, peaches contain more sucrose (6.66%) than they do fructose (0.93%) or glucose (1.47%). | 1 | Biochemistry |
The banteng was the second endangered species to be successfully cloned, and the first clone to survive beyond infancy. Scientists at Advanced Cell Technology in Worcester, Massachusetts, extracted DNA from skin cells of a dead male banteng, that were preserved in San Diego 's Frozen Zoo facility, and transferred it into eggs from domestic banteng cows, a process called somatic cell nuclear transfer. Thirty embryos were created and implanted in domestic banteng cows. Two were carried to term and delivered by Caesarian section. The first was born on 1 April 2003, and the second two days later. The second was euthanized, apparently suffering from large offspring syndrome (an overgrowth disorder), but the first survived and lived for seven years at the San Diego Zoo, where it died in April 2010 after it broke a leg and was euthanized. | 1 | Biochemistry |
The reagent is typically provided in two parts:
* A mixture of 2% sodium nitroprusside and 2% acetaldehyde in water (solution A)
* A solution of 2% sodium carbonate in water (solution B)
Separate storage of the aldehyde and base are necessary to prevent aldol polymerisation of the aldehyde.
When exposed to an amine, reaction with acetaldehyde produces the enamine, which subsequently reacts with sodium nitroprusside to the imine. Finally, the iminium salt is hydrolysed to the bright blue Simon-Awe complex.
Acetaldehyde can be replaced with acetone, in which case the reagent detects primary amines instead, giving a purple coloured product. | 3 | Analytical Chemistry |
For the calculation strategy of CASTp, alpha-shape and discrete-flow methods are applied to the protein binding site, also the measurement of pocket size by the program of CAST by Liang et al. in 1998, then updated by Tian et al. in 2018. Firstly, CAST identifies atoms which form the protein pocket, then calculates the volume and area, identifies the atoms forming the rims of pocket mouth, computes how many mouth openings for each pocket, predict the area and circumference of mouth openings, finally locates cavities and calculate their size. The secondary structures were calculated by DSSP. The single amino acid annotations were fetched from UniProt database, then mapped to PDB structures following residue-level information from SIFTS database. | 1 | Biochemistry |
; (1999 April);
Its an impressive memento which described the fascinating story of how his national team – Sri Lanka – blossomed out and established itself as International Champions of 1996/97 in Overs-limited cricket'. Perera has also captured here the brilliance, the philosophy and the pulsating drama of one-day internationals (ODIs) of that glorious period (1996–98) backed by highly informative and well tabulated appendices.
;Further Reading
* [https://web.archive.org/web/20100610050439/http://www.acumenbooks.co.uk/ajitintr.htm Sri Lanka were the Kings amongst Kings (1996–99)] Retrieved on 27 February 2009
* [http://sundaytimes.lk/011007/sportsm.html#s1LABEL3 Another masterpiece by Ajith Perera] Retrieved on 27 February 2009 | 3 | Analytical Chemistry |
Hydrogen-reduced iron is used as a source of food-grade iron powder, for food fortification and for oxygen scavenging. This elemental form is not absorbed as well as ferrous forms, but the oxygen-scavenging function keeps it attractive. Purity standards for this use are established in 1977. | 8 | Metallurgy |
Caesium carbonate facilitates the N-alkylation of compounds such as sulfonamides, amines, β-lactams, indoles, heterocyclic compounds, N-substituted aromatic imides, phthalimides, and other similar compounds. Research on these compounds has focused on their synthesis and biological activity. In the presence of sodium tetrachloroaurate (), caesium carbonate is very efficient mechanism for aerobic oxidation of different kinds of alcohols into ketones and aldehydes at room temperature without additional polymeric compounds. There is no acid formation produced when primary alcohols are used. The process of selective oxidation of alcohols to carbonyls had been quite difficult due to the nucleophilic character of the carbonyl intermediate. In the past Cr(VI) and Mn(VII) reagents have been used to oxidize alcohols, however, these reagents are toxic and comparatively expensive. Caesium carbonate can also be used in Suzuki, Heck, and Sonogashira synthesis reactions. Caesium carbonate produces carbonylation of alcohols and carbamination of amines more efficiently than some of the mechanisms that have been introduced in the past. Caesium carbonate can be used for sensitive synthesis when a balanced strong base is needed. | 0 | Organic Chemistry |
Transition metal porphyrin complexes are a family of coordination complexes of the conjugate base of porphyrins. Iron porphyrin complexes occur widely in Nature, which has stimulated extensive studies on related synthetic complexes. The metal-porphyrin interaction is a strong one such that metalloporphyrins are thermally robust. They are catalysts and exhibit rich optical properties, although these complexes remain mainly of academic interest. | 1 | Biochemistry |
Lyngbyastatins 1 and 3 are encoded for by a 52 kb biosynthetic gene cluster (BGC) containing one polyketide synthase (PKS)/non-ribosomal peptide synthetase (NRPS) hybrid (LbnA), four NRPSs (LbnB-D, LbnF), and one PKS (LbnE).
Biosynthesis commences with PKS activity — thiolation of propanoic (Lyngbyastatin 1) or butyric (Lyngbyastatin 3) acid and subsequent loading onto the ketosynthase (KS) of LbnA. An acyl unit from malonyl CoA is then coupled onto the initial substrate via an acyltransferase (AT) and then methylated at the alpha carbon through a C-methyltransferase (CMT) before an aminotransferase (AmT) conducts a transamination of the initial substrate carbonyl. The latter half of LbnA follows traditional NRPS activity containing condensation (C), adenylation (A), and thiolation (T) domains to couple 2-hydroxy-3-methylvaleric acid, which is believed to be formed from the 2-oxo analog through PKS ketoreductase (KR) activity.
LbnB, a traditional NRPS, adds glycine into the growing thioester by its amino group. LbnC is another traditional NRPS that adds L-leucine and glycine, respectively, except the L-leucine domain possesses an active N-methyltransferase (NMT) domain that methylates the nitrogen of L-leucine.
NRPS LbnD then adds L-valine, L-tyrosine, and L or D-valine, respectively to the growing molecule. PKS LbnE couples an acyl unit from malonyl-CoA onto the C-terminus of the valine residue before a C-methyltransferase methylates the carbon alpha to the thioester twice to produce a quarternary alpha carbon.
NRPS LbnF completes the biosynthesis by coupling L-alanine before the thioesterase (TE) domain conducts a head-to-tail cyclization to produce the final depsipeptide products. | 1 | Biochemistry |
McQuillan was awarded the Rosenhain Medal in 1965. She was on the Interservices Metallurgical Research Council until 1989 and in 1967 served as vice-president of the Institute of Metals. In 1968 she was fundamental to the First International Conference on Titanium in London. | 8 | Metallurgy |
These photosystems are light-driven redox centers, each consisting of an antenna complex that uses chlorophylls and accessory photosynthetic pigments such as carotenoids and phycobiliproteins to harvest light at a variety of wavelengths. Each antenna complex has between 250 and 400 pigment molecules and the energy they absorb is shuttled by resonance energy transfer to a specialized chlorophyll a at the reaction center of each photosystem. When either of the two chlorophyll a molecules at the reaction center absorb energy, an electron is excited and transferred to an electron-acceptor molecule. Photosystem I contains a pair of chlorophyll a molecules, designated P700, at its reaction center that maximally absorbs 700 nm light. Photosystem II contains P680 chlorophyll that absorbs 680 nm light best (note that these wavelengths correspond to deep red – see the visible spectrum). The P is short for pigment and the number is the specific absorption peak in nanometers for the chlorophyll molecules in each reaction center. This is the green pigment present in plants that is not visible to unaided eyes. | 5 | Photochemistry |
For organic compounds, the length of the C-O bond does not vary widely from 120 picometers. Inorganic carbonyls have shorter C-O distances: CO, 113; CO, 116; and COCl, 116 pm.
The carbonyl carbon is typically electrophilic. A qualitative order of electrophilicity is RCHO (aldehydes) > RCO (ketones) > RCOR' (esters) > RCONH (amides). A variety of nucleophiles attack, breaking the carbon-oxygen double bond.
Interactions between carbonyl groups and other substituents were found in a study of collagen. Substituents can affect carbonyl groups by addition or subtraction of electron density by means of a sigma bond. ΔHσ values are much greater when the substituents on the carbonyl group are more electronegative than carbon.
The polarity of C=O bond also enhances the acidity of any adjacent C-H bonds. Due to the positive charge on carbon and the negative charge on oxygen, carbonyl groups are subject to additions and/or nucleophilic attacks. A variety of nucleophiles attack, breaking the carbon-oxygen double bond, and leading to addition-elimination reactions. Nucleophiliic reactivity is often proportional to the basicity of the nucleophile and as nucleophilicity increases, the stability within a carbonyl compound decreases. The pK values of acetaldehyde and acetone are 16.7 and 19 respectively, | 0 | Organic Chemistry |
CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a genetic engineering technique that allows for precise editing of the genome. One application of CRISPR is gene knockout, which involves disabling or "knocking out" a specific gene in an organism.
The process of gene knockout with CRISPR involves three main steps: designing a guide RNA (gRNA) that targets a specific location in the genome, delivering the gRNA and a Cas9 enzyme (which acts as a molecular scissors) to the target cell, and then allowing the cell to repair the cut in the DNA. When the cell repairs the cut, it can either join the cut ends back together, resulting in a non-functional gene, or introduce a mutation that disrupts the gene's function.
This technique can be used in a variety of organisms, including bacteria, yeast, plants, and animals, and it allows scientists to study the function of specific genes by observing the effects of their absence. CRISPR-based gene knockout is a powerful tool for understanding the genetic basis of disease and for developing new therapies.
It is important to note that CRISPR-based gene knockout, like any genetic engineering technique, has the potential to produce unintended or harmful effects on the organism, so it should be used with caution. The coupled Cas9 will cause a double stranded break in the DNA. Following the same principle as zinc-fingers and TALENs, the attempts to repair these double stranded breaks often result in frameshift mutations that result in an nonfunctional gene. Non invasive CRISPR-Cas9 technology has successfully knocked out a gene associated in depression and anxiety in mice, being the first successful delivery passing through the blood–brain barrier to enable gene modification. | 1 | Biochemistry |
Although there are numerous benefits in using the SQT approach, drawbacks in its use have been identified. The major limitations include: lack of statistical criteria development within the framework, large database requirements, difficulties in chemical mixture application, and data interpretation can be laboratory intensive (Chapman 1989). The SQT does not evidently consider the bioavailability of complexed or sediment-associated contaminants (FDEP 1994). Lastly, it is difficult to translate laboratory toxicity results to biological effects seen in the field (Kamlet 1989). | 2 | Environmental Chemistry |
Specim, Spectral Imaging Ltd is a European technology firm headquartered in Oulu, Finland. Specim manufactures and sells imaging spectrographs, hyperspectral cameras and systems. Specim's airborne AISA hyperspectral cameras have been utilized for example in monitoring the environmental effects of major industrial catastrophes such as Deepwater Horizon oil spill and Red mud spill.
In 2010, Specim was widely credited for its Thermal Infrared Hyperspectral Cameras, including a position as a Prism Awards for Photonics Innovation finalist. The credited Specim Owl is world's first Thermal Hyperspectral Camera that can efficiently be used for outdoor surveillance and UAV applications without an external light source such as the Sun or the Moon.
In 2013, together with Germany's Forschungszentrum Jülich research centre, Specim developed and thoroughly tested the novel Hyplant airborne hyperspectral sensor. This was the first airborne sensor to map the fluorescence over large areas. Since then it has been used to map various types of vegetation all over Europe and also in the USA. This project is one step in assessing feasibility of possible new ESA satellite instrument that could provide global maps of vegetation fluorescence called the Fluorescence Explorer (FLEX). | 7 | Physical Chemistry |
Commonly, isocyanides are synthesized by dehydration of formamides. The formamide can be dehydrated with toluenesulfonyl chloride, phosphorus oxychloride, phosgene, diphosgene, or the Burgess reagent in the presence of a base such as pyridine or triethylamine.
The formamide precursors are, in turn, prepared from amines by formylation with formic acid or formyl acetyl anhydride.or from the Ritter reaction of alkenes (and other sources of carbocations) and hydrogen cyanide. | 0 | Organic Chemistry |
Super-resolution optical fluctuation imaging (SOFI) is a super-resolution technique that achieves spatial resolutions below the diffraction limit by post-processing analysis with correlation equations, similar to FCS. While original reports of SOFI used fluctuations from stationary, blinking of fluorophores, FCS has been combined with SOFI where fluctuations are produced from diffusing probes to produce super-resolution spatial maps of diffusion coefficients. This has been applied to understand diffusion and spatial properties of porous and confined materials. This includes agarose and temperature-responsive PNIPAM hydrogels, liquid crystals, and phase-separated polymers and RNA/protein condensates. | 7 | Physical Chemistry |
Rowley led the Peoples National Movement in the September 2015 general election, in which his party secured 23 out of 41 seats in the House of Representatives to form the government, defeating the previous Peoples Partnership coalition government. On 9 September 2015, Rowley was sworn in as Prime Minister of Trinidad and Tobago by President Anthony Carmona.
He becomes the seventh Prime Minister of Trinidad and Tobago and the second Tobago-born Prime Minister. Rowley again led the Peoples National Movement to victory in the 10 August 2020 general election for a second term in government under his premiership. He was sworn in as Prime Minister of Trinidad and Tobago on 19 August by President Paula-Mae Weekes at the Presidents House in St. Anns after the opposition party asked for recounts to be done in marginal constituencies.
During his tenure, on 5 February 2022, the Trinidad and Tobago coast guard fired upon a vessel with Venezuelan migrants while attempting to stop it, killing a nine-month-old baby and injuring his mother. The coast guard claimed that the shots were fired "in self-defense". Rowley deemed the action "legal and appropriate"; the Trinidadian police and coast guard opened an investigation of the event. | 9 | Geochemistry |
The extraction is performed in water with the addition of potassium hydroxide (KOH), sequestering agents, and hydrotropic surfactants. Heat is used to increase the solubility of humic acids and hence more potassium humate can be extracted. The resulting liquid is dried to produce the amorphous crystalline like product which can then be added as a granule to fertilizer. The potassium humate granules by way of chemical extraction lose their hydrophobic properties and are now soluble. | 9 | Geochemistry |
Isobornyl acetate is an organic compound consisting of the acetate ester or the terpenoid isoborneol. It is a colorless liquid with a pleasant pine-like scent, and it is produced on a multi-ton scale for this purpose. The compound is prepared by reaction of camphene with acetic acid in the presence of a strongly acidic catalyst such as sulfuric acid. Hydrolysis of isobornyl acetate gives isoborneol, a precursor to camphor.
Like many plant exudates, isobornyl acetate appears to have antifeedant properties. | 0 | Organic Chemistry |
Various kits have a 93 to 95% sensitivity (true positive rate). For hospitalized patients, one study found the specificity to be about 50% (related to false positive rate) in the diagnosis of thrombotic disease.
* False positive readings can be due to various causes: liver disease, high rheumatoid factor, inflammation, malignancy, trauma, pregnancy, recent surgery as well as advanced age.
* False negative readings can occur if the sample is taken either too early after thrombus formation or if testing is delayed for several days. Additionally, the presence of anti-coagulation can render the test negative because it prevents thrombus extension. The anti-coagulation medications dabigatran and rivaroxaban decrease D-dimer levels but do not interfere with the D-dimer assay.
* False values may be obtained if the specimen collection tube is not sufficiently filled (false low value if underfilled and false high value if overfilled). This is due to the dilutional effect of the anticoagulant (the blood must be collected in a 9:1 blood to anticoagulant ratio).
* Likelihood ratios are derived from sensitivity and specificity to adjust pretest probability.
In interpretation of the D-dimer, for patients over age 50, a value of (patient's age) × 10 μg/L may be abnormal. | 1 | Biochemistry |
In molecular biology, the Ycf4 protein is involved in the assembly of the photosystem I complex which is part of an energy-harvesting process named photosynthesis. Without Ycf4, photosynthesis would be inefficient affecting plant growth. Ycf4 is located in the thylakoid membrane of the chloroplast. Ycf4 is important for the light dependent reaction of photosynthesis.
To date, three thylakoid proteins involved in the stable accumulation of PSI have been identified, these are as follows:
* BtpA ([http://www.ebi.ac.uk/interpro/IEntry?ac=IPR005137 INTERPRO]),
* Ycf3
* Ycf4.
The Ycf4 protein is firmly associated with the thylakoid membrane, presumably through a transmembrane domain. Ycf4 co-fractionates with a protein complex larger than PSI upon sucrose density gradient centrifugation of solubilised thylakoids.
Ycf is an acronym standing for hypothetical chloroplast open reading frame. | 5 | Photochemistry |
Sintering and hot isostatic pressing are processing techniques used to densify materials from a loosely packed "green body" into a solid object with physically merged grains. Sintering occurs below the melting point, and causes adjacent particles to merge at their boundaries, creating a strong bond between them. In hot isostatic pressing, a sintered material is placed in a pressure vessel and compressed from all directions (isostatically) in an inert atmosphere to affect densification. | 8 | Metallurgy |
The vulcanization of rubber results in crosslinking groups which consist of disulfide (and polysulfide) bonds; in analogy to the role of disulfides in proteins, the S−S linkages in rubber strongly affect the stability and rheology of the material. Although the exact mechanism underlying the vulcanization process is not entirely understood (as multiple reaction pathways are present but the predominant one is unknown), it has been extensively shown that the extent to which the process is allowed to proceed determines the physical properties of the resulting rubber- namely, a greater degree of crosslinking corresponds to a stronger and more rigid material. The current conventional methods of rubber manufacturing are typically irreversible, as the unregulated reaction mechanisms can result in complex networks of sulfide linkages; as such, rubber is considered to be a thermoset material. | 0 | Organic Chemistry |
The Society has hosted scientific technical meetings since 1902 including its biannual meetings in the spring and fall of each year. The ECS biannual meetings bring together the most active researchers in academia, government, and industry—both professionals and students—to engage, discuss, and innovate in the areas of electrochemistry solid-state science, and related technology. They are a premier destination—in person or online—for industry professionals to experience five days of learning, technical presentations, business development, and networking. ECS also sponsors meetings for other renowned scientific organizations including the Storage X International Symposium Series, the International Meeting on Chemical Sensors, and the International Symposium on Solid Oxide Fuel Cells. | 7 | Physical Chemistry |
Photosystem II is damaged by light irrespective of light intensity. The quantum yield of the damaging reaction in typical leaves of higher plants exposed to visible light, as well as in isolated thylakoid membrane preparations, is in the range of 10 to 10 and independent of the intensity of light. This means that one PSII complex is damaged for every 10-100 million photons that are intercepted. Therefore, photoinhibition occurs at all light intensities and the rate constant of photoinhibition is directly proportional to light intensity. Some measurements suggest that dim light causes damage more efficiently than strong light. | 5 | Photochemistry |
Mill scale is a complex oxide that contains around 70% iron with traces of nonferrous metals and alkaline compounds. Reduced iron powder may be obtained by conversion of mill scale into a single highest oxide i.e. hematite () followed by reduction with hydrogen. Shahid and Choi reported the reverse co-precipitation method for the synthesis of magnetite () from mill scale and used for multiple environmental applications such as nutrient recovery, ballasted coagulation in activated sludge process, and heavy metal remediation in an aqueous environment. | 8 | Metallurgy |
Blood based protein biomarkers are often used as a diagnostic test that usually monitor one or more protein that are indicative of the presence of disease or disorder or the presence of a disease/disorder subphtnotype. Such a Blood based protein biomarker-based test can aoften be used Bas prognosticator of disease outcome. An example is neuronal Ubiquitin carboxy-terminal hydrolase L1 (UCH-L1) and Glial fibrillary acidic protein (GFAP) can aid in the diagnosis of the presence a cranial lesion among moderate to mild TBI patients that is otherwise only diagnosable with the use of a CT scan of the head. | 1 | Biochemistry |
Stress corrosion cracking (SCC) happens when a stressed material is in a corrosive (chemically destructive) environment. One example of SSC embrittlement is when moisture increases static fatigue effects in glass. SCC is also seen in hydrogen embrittlement, embrittlement of some polymers, and more. | 8 | Metallurgy |
The types of spectroscopy also can be distinguished by the nature of the interaction between the energy and the material. These interactions include:
* Absorption spectroscopy: Absorption occurs when energy from the radiative source is absorbed by the material. Absorption is often determined by measuring the fraction of energy transmitted through the material, with absorption decreasing the transmitted portion.
* Emission spectroscopy: Emission indicates that radiative energy is released by the material. A material's blackbody spectrum is a spontaneous emission spectrum determined by its temperature. This feature can be measured in the infrared by instruments such as the atmospheric emitted radiance interferometer. Emission can also be induced by other sources of energy such as flames, sparks, electric arcs or electromagnetic radiation in the case of fluorescence.
* Elastic scattering and reflection spectroscopy determine how incident radiation is reflected or scattered by a material. Crystallography employs the scattering of high energy radiation, such as x-rays and electrons, to examine the arrangement of atoms in proteins and solid crystals.
* Impedance spectroscopy: Impedance is the ability of a medium to impede or slow the transmittance of energy. For optical applications, this is characterized by the index of refraction.
* Inelastic scattering phenomena involve an exchange of energy between the radiation and the matter that shifts the wavelength of the scattered radiation. These include Raman and Compton scattering.
* Coherent or resonance spectroscopy are techniques where the radiative energy couples two quantum states of the material in a coherent interaction that is sustained by the radiating field. The coherence can be disrupted by other interactions, such as particle collisions and energy transfer, and so often require high intensity radiation to be sustained. Nuclear magnetic resonance (NMR) spectroscopy is a widely used resonance method, and ultrafast laser spectroscopy is also possible in the infrared and visible spectral regions.
* Nuclear spectroscopy are methods that use the properties of specific nuclei to probe the local structure in matter, mainly condensed matter, molecules in liquids or frozen liquids and bio-molecules.
* Quantum logic spectroscopy is a general technique used in ion traps which enables precision spectroscopy of ions with internal structures that preclude laser cooling, state manipulation, and detection. Quantum logic operations enable a controllable ion to exchange information with a co-trapped ion that has a complex or unknown electronic structure. | 7 | Physical Chemistry |
Thermodynamicists use this factor (Z) to alter the ideal gas equation to account for compressibility effects of real gases. This factor represents the ratio of actual to ideal specific volumes. It is sometimes referred to as a "fudge-factor" or correction to expand the useful range of the ideal gas law for design purposes. Usually this Z value is very close to unity. The compressibility factor image illustrates how Z varies over a range of very cold temperatures. | 7 | Physical Chemistry |
A mixture of bromo acetal 1 (549 mg, 1.78 mmol), AIBN (30.3 mg, 0.185 mmol), and BuSnH (0.65 mL, 2.42 mmol) in dry benzene (12 mL) was heated under reflux for 1 hour and then evaporated under reduced pressure. Silicagel column chromatography of the crude product with hexane–EtOAc (92:8) as eluant gave tetrahydropyran 2 (395 mg, 97%) as an oily mixture of two diastereomers. (c 0.43, CHCl); IR (CHCl):1732 cm–1;1H NMR (CDCl)δ 4.77–4.89 (m, 0.6H), 4.66–4.69 (m, 0.4H), 3.40–4.44 (m, 4H), 3.68 (s, 3H), 2.61 (dd, J = 15.2, 4.2 Hz, 1H), 2.51 (dd, J = 15.2, 3.8 Hz, 1H), 0.73–1.06 (m, 3H); mass spectrum: m/z 215 (M+–Me); Anal. Calcd for CHO: C, 62.6; H, 9.65. Found: C, 62.6; H, 9.7. | 0 | Organic Chemistry |
IPA can be converted in the liver or kidneys to 3-indoleacrylic acid, which is subsequently conjugated with glycine, forming indolylacryloyl glycine. | 1 | Biochemistry |
The discovery that a hormone can influence phosphoinositide metabolism was made by Mabel R. Hokin (1924–2003) and her husband Lowell E. Hokin in 1953, when they discovered that radioactive P phosphate was incorporated into the phosphatidylinositol of pancreas slices when stimulated with acetylcholine. Up until then phospholipids were believed to be inert structures only used by cells as building blocks for construction of the plasma membrane.
Over the next 20 years, little was discovered about the importance of PIP metabolism in terms of cell signaling, until the mid-1970s when Robert H. Michell hypothesized a connection between the catabolism of PIP and increases in intracellular calcium (Ca) levels. He hypothesized that receptor-activated hydrolysis of PIP produced a molecule that caused increases in intracellular calcium mobilization. This idea was researched extensively by Michell and his colleagues, who in 1981 were able to show that PIP is hydrolyzed into DAG and IP by a then unknown phosphodiesterase. In 1984 it was discovered that IP acts as a secondary messenger that is capable of traveling through the cytoplasm to the endoplasmic reticulum (ER), where it stimulates the release of calcium into the cytoplasm.
Further research provided valuable information on the IP pathway, such as the discovery in 1986 that one of the many roles of the calcium released by IP is to work with DAG to activate protein kinase C (PKC). It was discovered in 1989 that phospholipase C (PLC) is the phosphodiesterase responsible for hydrolyzing PIP into DAG and IP. Today the IP signaling pathway is well mapped out, and is known to be important in regulating a variety of calcium-dependent cell signaling pathways. | 1 | Biochemistry |
Mass spectrometry (MS) can identify proteins and their relative levels, hence it can be used to study protein expression. When used in combination with affinity purification, mass spectrometry (AP/MS) can be used to study protein complexes, that is, which proteins interact with one another in complexes and in which ratios. In order to purify protein complexes, usually a "bait" protein is tagged with a specific protein or peptide that can be used to pull out the complex from a complex mix. The purification is usually done using an antibody or a compound that binds to the fusion part. The proteins are then digested into short peptide fragments and mass spectrometry is used to identify the proteins based on the mass-to-charge ratios of those fragments. | 1 | Biochemistry |
The embryo transfer procedure starts by placing a speculum in the vagina to visualize the cervix, which is cleansed with saline solution or culture media. A transfer catheter is loaded with the embryos and handed to the clinician after confirmation of the patient's identity. The catheter is inserted through the cervical canal and advanced into the uterine cavity. Several types of catheters are used for this process, however, there is good evidence that using a soft vs a hard transfer catheter can increase the chances of clinical pregnancy.
There is good and consistent evidence of benefit in ultrasound guidance, that is, making an abdominal ultrasound to ensure correct placement, which is 1–2 cm from the uterine fundus. There is evidence of a significant increase in clinical pregnancy using ultrasound guidance compared with only "clinical touch", as well as performing the transfer with hyaluronic acid enriched transfer media. Anesthesia is generally not required. Single embryo transfers in particular require accuracy and precision in placement within the uterine cavity. The optimal target for embryo placement, known as the maximal implantation potential (MIP) point, is identified using 3D/4D ultrasound. However, there is limited evidence that supports deposition of embryos in the midportion of the uterus.
After insertion of the catheter, the contents are expelled and the embryos are deposited. Limited evidence supports making trial transfers before performing the procedure with embryos. After expulsion, the duration that the catheter remains inside the uterus has no effect on pregnancy rates. Limited evidence suggests avoiding negative pressure from the catheter after expulsion. After withdrawal, the catheter is handed to the embryologist, who inspects it for retained embryos.
In the process of zygote intrafallopian transfer (ZIFT), eggs are removed from the woman, fertilised, and then placed in the woman's fallopian tubes rather than the uterus. | 1 | Biochemistry |
The parent compound can be prepared by heating urea at 150 °C for ~6 hours until it gets slightly cloudy, then recrystallizing from water. After that, it can be recrystallized repeatedly from 2% sodium hydroxide solution and water to finally get base-free crystalline needles of the monohydrate which are free of cyanuric acid. While heating, a lot of ammonia is expelled:
Under related conditions, pyrolysis of urea affords triuret .
In general, organic biurets (those with alkyl or aryl groups in place of one or more H atoms) are prepared by trimerization of isocyanates. For example, the trimer of 1,6-hexamethylene diisocyanate is also known as HDI-biuret.
In the anhydrous form, the molecule is planar and unsymmetrical in the solid state owing to intramolecular hydrogen bonding. The terminal C–N distances of 1.327 and 1.334 Å are shorter than the internal C–N distances of 1.379 and 1.391 Å. The C=O bond distances 1.247 and 1.237 Å. It crystallizes from water as the monohydrate. | 0 | Organic Chemistry |
* Platyhelminthes (flatworms) and Nematoda (roundworms).
Code 14 differs from code 9 (the echinoderm and flatworm mitochondrial code) only by translating UAA to Tyr rather than STOP. A study in 2000 has found no evidence that the codon UAA codes for Tyr in the flatworms but other opinions exist. There are very few GenBank records that are translated with code 14 but a test translation shows that re-translating these records with code 9 can cause premature terminations. More recently, UAA has been found to code for tyrosine in the nematodes Radopholus similis and Radopholus arabocoffeae. | 1 | Biochemistry |
Malonyl-CoA is formed in the first step of mitochondrial fatty acid synthesis (mtFASII) from malonic acid by malonyl-CoA synthetase (ACSF3). | 1 | Biochemistry |
The Lauritzen–Hoffman plot (right) models the three different regimes when (logG) + U*/k(T-T) is plotted against (TΔT). It can be used to describe the rate at which secondary nucleation competes with lateral addition at the growth front among the different temperatures. This theory can be used to help understand the preferences of nucleation and growth based on the polymer's properties including its standard melting temperature. | 7 | Physical Chemistry |
Areteia Therapeutics is currently conducting three global Phase III clinical trials of dexpramipexole in eosinophil-associated asthma as listed below.
EXHALE-2: a global Phase III clinical trial to evaluate the efficacy and safety of dexpramipexole as an add-on oral therapy in participants with inadequately controlled eosinophilic asthma, is currently recruiting people ≥12 years old with a documented physician diagnosis of asthma who require medium to high dose inhaled corticosteroids with at least one other controller medicine and a history of asthma exacerbations. The study will assess the effects of two different doses of dexpramipexole on exacerbation rates and lung function.
EXHALE-3: a global Phase III clinical trial to evaluate the efficacy and safety of dexpramipexole as an add-on oral therapy in participants with inadequately controlled eosinophilic asthma, is currently recruiting people ≥12 years old with a documented physician diagnosis of asthma who require medium to high dose inhaled corticosteroids with at least one other controller medicine and a history of asthma exacerbations. The study will assess the effects of two different doses of dexpramipexole on exacerbation rates and lung function.
EXHALE-4: a global Phase III clinical trial to evaluate dexpramipexole as an add-on oral therapy in participants with inadequately controlled eosinophilic asthma, is currently recruiting people ≥12 years old with a documented physician diagnosis of asthma who require treatment with at least low-dose inhaled corticosteroids and one other controller medicine. The study will assess improvements in lung function, asthma control, and quality of life. | 4 | Stereochemistry |
EosFP is a photoactivatable green to red fluorescent protein. Its green fluorescence (516 nm) switches to red (581 nm) upon UV irradiation of ~390 nm (violet/blue light) due to a photo-induced modification resulting from a break in the peptide backbone near the chromophore. Eos was first discovered as a tetrameric protein in the stony coral Lobophyllia hemprichii. Like other fluorescent proteins, Eos allows for applications such as the tracking of fusion proteins, multicolour labelling and tracking of cell movement. Several variants of Eos have been engineered for use in specific study systems including mEos2, mEos4 and CaMPARI. | 1 | Biochemistry |
As depicted in the five photographs below, Dr. Perera perhaps became the first disabled person in Sri Lanka to be recognised in Sri Lanka for his outstanding voluntary contributions to the community – to the promotion and establishment of Accessibility to the Built environment, enhancing safety and social inclusion with empowerment of people with all abilities.
Perera has aggressively promoted in Sri Lanka the concept of Social Inclusion for All with the Vision: Accessible Sri Lanka focusing on built environments that does not marginalise or cause discrimination against people on the grounds of inevitable diversity in ability and campaigned against arbitrary categorisation of people.
Undeterred by his personal adversity, playing eight different roles over 17 consecutive years for the promotion of Accessibility Rights in Sri Lanka, he was recognised and appreciated in 2016 for his outstanding voluntary contributions to the community – please see below.
First, in September 2016, he was named the "Sri Lankan of the Year 2016" under the category of Unsung Hero; and then on the UN Day in October 2016 he was presented with the APEX award by the United Nations Association of Sri Lanka. | 3 | Analytical Chemistry |
Electrochemical engineering combines the study of heterogeneous charge transfer at electrode/electrolyte interphases with the development of practical materials and processes. Fundamental considerations include electrode materials and the kinetics of redox species. The development of the technology involves the study of the electrochemical reactors, their potential and current distribution, mass transport conditions, hydrodynamics, geometry and components as well as the quantification of its overall performance in terms of reaction yield, conversion efficiency, and energy efficiency. Industrial developments require further reactor and process design, fabrication methods, testing, and product development.
Electrochemical engineering considers current distribution, fluid flow, mass transfer, and the kinetics of the electro reactions to design efficient electrochemical reactors.
Most electrochemical operations are performed in filter-press reactors with parallel plate electrodes or, less often, in stirred tanks with rotating cylinder electrodes. Fuel cell and flow battery stacks are types of filter-press reactors. Most of them are continuous operations. | 7 | Physical Chemistry |
Carbon compounds can be distinguished as either organic or inorganic, and dissolved or particulate, depending on their composition. Organic carbon forms the backbone of key component of organic compounds such as – proteins, lipids, carbohydrates, and nucleic acids. Inorganic carbon is found primarily in simple compounds such as carbon dioxide, carbonic acid, bicarbonate, and carbonate (CO, HCO, HCO, CO respectively).
Marine carbon is further separated into particulate and dissolved phases. These pools are operationally defined by physical separation – dissolved carbon passes through a 0.2 μm filter, and particulate carbon does not.
There are two main types of inorganic carbon that are found in the oceans. Dissolved inorganic carbon (DIC) is made up of bicarbonate (HCO), carbonate (CO) and carbon dioxide (including both dissolved CO and carbonic acid HCO). DIC can be converted to particulate inorganic carbon (PIC) through precipitation of CaCO (biologically or abiotically). DIC can also be converted to particulate organic carbon (POC) through photosynthesis and chemoautotrophy (i.e. primary production). DIC increases with depth as organic carbon particles sink and are respired. Free oxygen decreases as DIC increases because oxygen is consumed during aerobic respiration.
Particulate inorganic carbon (PIC) is the other form of inorganic carbon found in the ocean. Most PIC is the CaCO that makes up shells of various marine organisms, but can also form in whiting events. Marine fish also excrete calcium carbonate during osmoregulation.
Some of the inorganic carbon species in the ocean, such as bicarbonate and carbonate, are major contributors to alkalinity, a natural ocean buffer that prevents drastic changes in acidity (or pH). The marine carbon cycle also affects the reaction and dissolution rates of some chemical compounds, regulates the amount of carbon dioxide in the atmosphere and Earth's temperature. | 9 | Geochemistry |
Ionophores are widely used in cell physiology experiments and biotechnology as these compounds can effectively perturb gradients of ions across biological membranes and thus they can modulate or enhance the role of key ions in the cell. Many ionophores have shown antibacterial and antifungal activities. Some of them also act against insects, pests and parasites. Some ionophores have been introduced into medicinal products for dermatological and veterinary use. A large amount of research has been directed toward investigating novel antiviral, anti-inflammatory, anti-tumor, antioxidant and neuroprotective properties of different ionophores.
Chloroquine is an antimalarial and antiamebic drug. It is also used in the management of rheumatoid arthritis and lupus erythematosus. Pyrithione is used as an anti-dandruff agent in medicated shampoos for seborrheic dermatitis. It also serves as an anti-fouling agent in paints to cover and protect surfaces against mildew and algae. Clioquinol and PBT2 are 8-hydroxyquinoline derivatives. Clioquinol has antiprotozoal and topical antifungal properties, however its use as an antiprotozoal agent has widely restricted because of neurotoxic concerns. Clioquinol and PBT2 are currently being studied for neurodegenerative diseases, such as Alzheimers disease, Huntingtons disease and Parkinson's disease. Gramicidin is used in throat lozenges and has been used to treat infected wounds. Epigallocatechin gallate is used in many dietary supplements and has shown slight cholesterol-lowering effects. Quercetin has a bitter flavor and is used as a food additive and in dietary supplements. Hinokitiol (ß-thujaplicin) is used in commercial products for skin, hair and oral care, insect repellents and deodorants. It is also used as a food additive, shelf-life extending agent in food packaging, and wood preservative in timber treatment.
Polyene antimycotics, such as nystatin, natamycin and amphotericin B, are a subgroup of macrolides and are widely used antifungal and antileishmanial medications. These drugs act as ionophores by binding to ergosterol in the fungal cell membrane and making it leaky and permeable for K and Na ions, as a result contributing to fungal cell death.
Carboxylic ionophores, i.e. monensin, lasalocid, salinomycin, narasin, maduramicin, semduramycin and laidlomycin, are marketed globally and widely used as anticoccidial feed additives to prevent and treat coccidiosis in poultry. Some of these compounds have also been used as growth and production promoters in certain ruminants, such as cattle, and chickens, however this use has been mainly restricted because of safety issues.
Zinc ionophores have been shown to inhibit replication of various viruses in vitro, including coxsackievirus, equine arteritis virus, coronavirus, HCV, HSV, HCoV-229E, HIV, mengovirus, MERS-CoV, rhinovirus, SARS-CoV-1, Zika virus. | 7 | Physical Chemistry |
Moureu was widely respected for his research work. As part of his research on acrylic acid and its derivatives, he was the first to synthesize acrylonitrile in 1893.
In addition, he studied acetylene compounds, phenolic compounds, plant essences, and rare gases found in wells and mines.
During the war, Moureu researched acrolein and sulfur mustard gas, working with his student Charles Dufraisse.
Acrolein was an extremely unstable compound, which tended to polymerize on contact with air. Already familiar with the preparation of acrolein, Moureu and Dufraisse were able to develop a way to stabilize it after carefully studying the processes by which it altered. Their work led to the use of acrolein and later benzyl iodide in weapons.
Their research also had great impact and long-lasting significance after the war. It was first published in the Bulletin of the Chemical Society of France in 1922.
The autoxidation reactions that Moureu and Dufraisse described occur spontaneously in most organic products in the presence of oxygen from the air and certain catalysts. Autoxidation affects virtually all living organisms. Moureu identified catalysts that could trigger such reactions, and other compounds that could slow or inhibit such reactions. He called the inhibitors "antioxygens", now known as "antioxidants".
Moureu is best known for this pioneering research. It has led to the use of antioxidants in the rubber and vegetable oil industries,
and to widespread applications in foods and medicines. Antioxidants are added to slow the spoiling of foods and the aging of rubber.
Moureu's work with sulfur mustard also became important after the war, as later researchers realized that some of the chemicals that were in mustard gas could be used as anti-cancer drugs, suppressing the division and proliferation of blood and bone marrow cells in leukaemia and lymphatic tumours.
With Adolphe Lepape, Moureu studied rare gases including krypton and xenon.
He developed methods for analyzing the gaseous components of mineral springs, and carried out comparative analyses of at least 108 springs. | 0 | Organic Chemistry |
Embryo transfer techniques allow top quality female livestock to have a greater influence on the genetic advancement of a herd or flock in much the same way that artificial insemination has allowed greater use of superior sires. ET also allows the continued use of animals such as competition mares to continue training and showing, while producing foals. The general epidemiological aspects of embryo transfer indicates that the transfer of embryos provides the opportunity to introduce genetic material into populations of livestock while greatly reducing the risk for transmission of infectious diseases. Recent developments in the sexing of embryos before transfer and implanting has great potential in the dairy and other livestock industries.
Embryo transfer is also used in laboratory mice. For example, embryos of genetically modified strains that are difficult to breed or expensive to maintain may be stored frozen, and only thawed and implanted into a pseudopregnant dam when needed.
On February 19, 2020, the first pair of Cheetah cubs to be conceived through embryo transfer from a surrogate cheetah mother was born at Columbus Zoo in Ohio. | 1 | Biochemistry |
Gay-Lussac's law states that:
Therefore,
* , or
* , or
:where P is the pressure, T is the absolute temperature, and k is another proportionality constant. | 7 | Physical Chemistry |
In 1848, Louis Pasteur became the first scientist to discover chirality and enantiomers while he was working with tartaric acid. During the experiments, he noticed that there were two crystal structures produced but these structures looked to be non-superimposable mirror images of each other; this observation of isomers that were non-superimposable mirror images became known as enantiomers. A couple years later, in 1857, Pasteur then discovered enantioselectivity when he noticed that the two enantiomer structures he had previously discovered metabolized at much different speeds. This suggested that one configuration was preferred over the other in vivo. As organic chemistry knowledge became more advanced, the discovery of enantioselectivity was used in the creation of enantiopure drugs. | 4 | Stereochemistry |
Initiation of translation in bacteria involves the assembly of the components of the translation system, which are: the two ribosomal subunits (50S and 30S subunits); the mature mRNA to be translated; the tRNA charged with N-formylmethionine (the first amino acid in the nascent peptide); guanosine triphosphate (GTP) as a source of energy, and the three prokaryotic initiation factors IF1, IF2, and IF3, which help the assembly of the initiation complex. Variations in the mechanism can be anticipated.
The ribosome has three active sites: the A site, the P site, and the E site. The A site is the point of entry for the aminoacyl tRNA (except for the first aminoacyl tRNA, which enters at the P site). The P site is where the peptidyl tRNA is formed in the ribosome. And the E site which is the exit site of the now uncharged tRNA after it gives its amino acid to the growing peptide chain. | 1 | Biochemistry |
A system with three components is called a ternary system. At constant pressure the maximum number of independent variables is three – the temperature and two concentration values. For a representation of ternary equilibria a three-dimensional phase diagram is required. Often such a diagram is drawn with the composition as a horizontal plane and the temperature on an axis perpendicular to this plane. To represent composition in a ternary system an equilateral triangle is used, called Gibbs triangle (see also Ternary plot).
The temperature scale is plotted on the axis perpendicular to the composition triangle. Thus, the space model of a ternary phase diagram is a right-triangular prism. The prism sides represent corresponding binary systems A-B, B-C, A-C.
However, the most common methods to present phase equilibria in a ternary system are the following:
1) projections on the concentration triangle ABC of the liquidus, solidus, solvus surfaces;
2) isothermal sections;
3) vertical sections. | 7 | Physical Chemistry |
Some capillary techniques provide also a chamber like arrangement, however, there is no filter between the cells and the test substance. Quantitative results are gained by the multiwell type of this probe using 4-8-12-channel pipettes. Accuracy of the pipette and increased number of the parallel running samples is the great advantage of this test.
Counting of cells: positive responder cells are count from the lower chamber (long incubation time) or from the filter (short incubation time). For detection of cells general staining techniques (e.g. trypan blue) or special probes (e.g. mt-dehydrogenase detection with MTT assay) are used. Labelled (e.g. fluorochromes) cells are also used, in some assays cells get labelled during transmigration the filter. | 1 | Biochemistry |
Direct ammonia fuel cells are researched for this exact reason and new studies presented a new integrated solar-based ammonia synthesis and fuel cell. The solar base follows from excess solar power that is used to synthesize ammonia. This is done by using an ammonia electrolytic cell (AEC) in combination with a proton exchange membrane (PEM) fuel cell. When a dip in solar power occurs, a direct ammonia fuel cell kicks into action providing the lacking energy. This recent research (2020) is a clear example of efficient use of energy, which is essentially done by temporary storage and use of ammonia as a fuel. Storage of energy in ammonia does not degrade over time, which is the case with batteries and flywheels. This provides long-term energy storage. This compact form of energy has the additional advantage that excess energy can easily be transported to other locations. This needs to be done with high safety measures due to the toxicity of ammonia for humans. Further research needs to be done to complement this system with wind energy and hydro-power plants to create a hybrid system to limit the interruptions in power supply. It is necessary to also investigate on the economic performance of the proposed system. Some scientists envision a new ammonia economy that is almost the same as the oil industry, but with the enormous advantage of inexhaustible carbon-free power. This so called green ammonia is considered as a potential fuel for super large ships. South Korean shipbuilder DSME plans on commercializing these ships by 2025. | 5 | Photochemistry |
Oxazolidinones can be prepared from amino acids or readily available amino alcohols. A large number of oxazolidinones are commercially available, including the four below.
Acylation of the oxazolidinone is achieved by deprotonation with n-butyllithium and quench with an acyl chloride. | 4 | Stereochemistry |
Chirality-induced spin selectivity (CISS) refers to multiple phenomena where handedness of a chiral chemical compound influences the spin of transmitted or emitted electrons.
Experiments were able to demonstrate the effect in the form of polarization of electrons scattered from chiral molecules, spin-dependent transmission probabilities through layers of chiral molecules, spin-selectivity of electron-transport in a chiral medium and enantio-selectivity in chemical reactions induced by spin-polarized electrons.
Theoretical models were able to qualitatively explain the effect using spin-orbit coupling (SOC). But quantitatively the predicted effect was always orders of magnitude smaller than what was measured in experiments. The mechanism underlying CISS is not completely understood. | 4 | Stereochemistry |
RNA-protein interactions have been investigated through a three-hybrid variation of the two-hybrid technique. In this case, a hybrid RNA molecule serves to adjoin together the two protein fusion domains—which are not intended to interact with each other but rather the intermediary RNA molecule (through their RNA-binding domains). Techniques involving non-fusion proteins that perform a similar function, as described in the non-fusion proteins section above, may also be referred to as three-hybrid methods. | 1 | Biochemistry |
In biological nitrification, the oxidation of to hydroxylamine is mediated by the ammonia monooxygenase (AMO). Hydroxylamine oxidoreductase (HAO) further oxidizes hydroxylamine to nitrite.
Cytochrome P460, an enzyme found in the ammonia-oxidizing bacteria Nitrosomonas europea, can convert hydroxylamine to nitrous oxide, a potent greenhouse gas.
Hydroxylamine can also be used to highly selectively cleave asparaginyl-glycine peptide bonds in peptides and proteins. It also bonds to and permanently disables (poisons) heme-containing enzymes. It is used as an irreversible inhibitor of the oxygen-evolving complex of photosynthesis on account of its similar structure to water. | 0 | Organic Chemistry |
In organic chemistry, transamidification is the process of exchanging the subunits of a peptide, amide or ester compound with another amine or fatty acid to produce a new amide or peptide. The process has been used for the production of emulsifiers and dispersing agents and oil drilling fluids. | 0 | Organic Chemistry |
As many as 20% of human tumors are caused by viruses. Some such viruses that are commonly recognized include HPV, T-cell Leukemia virus type I, and hepatitis B.
Viral oncogenesis are most common with DNA and RNA tumor viruses, most frequently the retroviruses. There are two types of oncogenic retroviruses: acute transforming viruses and non-acute transforming viruses. Acute transforming viruses induce a rapid tumor growth since they carry viral oncogenes in their DNA/RNA to induce such growth. An example of an acute transforming virus is the Rous Sarcoma Virus (RSV) that carry the v-src oncogene. v-Src is part of the c-src, which is a cellular proto-oncogene that stimulates rapid cell growth and expansion. A non-acute transforming virus on the other hand induces a slow tumor growth, since it does not carry any viral oncogenes. It induces tumor growth by transcriptionally activating the proto-oncogenes particularly the long terminal repeat (LTR) in the proto-oncogenes.
Viral Oncogenesis through transformation can occur via 2 mechanisms:
# The tumor virus can introduce and express a "transforming" gene either through the integration of DNA or RNA into the host genome.
# The tumor virus can alter expression on preexisting genes of the host.
One or both of these mechanisms can occur in the same host cell. | 1 | Biochemistry |
In order to study its potential as a cancer therapy target, Globo H has been synthesized in the laboratory. One synthesis is achieved by first building two trisaccharides from their component sugars, and then linking them. The trisaccharides, with most of their functional groups protected to prevent side reactions, are linked by creating the GalNAcβ(1-3)Gal bond. A thioethyl group is added to the 1 position on one of the protected galactose rings, and in the presence of methyl triflate, this reacts with the hydroxyl group on the 3 position of the other galactose to link the trisaccharides and form the hexasaccharide. The ceramide is added to the 1 position of the terminal glucose ring after hexasaccharide formation. | 1 | Biochemistry |
Inhalation of chloromethane gas produces central nervous system effects similar to alcohol intoxication. The TLV is 50 ppm and the MAC is the same. Prolonged exposure may have mutagenic effects. | 2 | Environmental Chemistry |
Philip Joseph Kocienski (born 23 December 1946) is a British organic chemist. He is an Emeritus Professor at the University of Leeds. | 0 | Organic Chemistry |
Transient liquid phase diffusion bonding (TLPDB) is a joining process that has been applied for bonding many metallic and ceramic systems which cannot be bonded by conventional fusion welding techniques. The bonding process produces joints with a uniform composition profile, tolerant of surface oxides and geometrical defects. The bonding technique has been exploited in a wide range of applications, from the production and repair of turbine engines in the aerospace industry, to nuclear power plants, and in making connections to integrated circuit dies as a part of the microelectronics industry. | 8 | Metallurgy |
The process of binding is central in determining the "strength" of promoters, that is the relative estimation of how "well" a promoter perform the expression of a gene under specific circumstances. Brewster et al., using a simple thermodynamical model based on the postulate that transcriptional activity is proportional to the probability of finding the RNA polymerase bound at the promoter, obtained predictions of the scaling of the RNA polymerase binding energy. This models support the relationship between the probability of binding and the output of gene expression | 1 | Biochemistry |
Cavity ring-down spectroscopy (CRDS) is a highly sensitive optical spectroscopic technique that enables measurement of absolute optical extinction by samples that scatter and absorb light. It has been widely used to study gaseous samples which absorb light at specific wavelengths, and in turn to determine mole fractions down to the parts per trillion level. The technique is also known as cavity ring-down laser absorption spectroscopy (CRLAS).
A typical CRDS setup consists of a laser that is used to illuminate a high-finesse optical cavity, which in its simplest form consists of two highly reflective mirrors. When the laser is in resonance with a cavity mode, intensity builds up in the cavity due to constructive interference. The laser is then turned off in order to allow the measurement of the exponentially decaying light intensity leaking from the cavity. During this decay, light is reflected back and forth thousands of times between the mirrors giving an effective path length for the extinction on the order of a few kilometers.
If a light-absorbing material is now placed in the cavity, the mean lifetime decreases as fewer bounces through the medium are required before the light is fully absorbed, or absorbed to some fraction of its initial intensity. A CRDS setup measures how long it takes for the light to decay to 1/e of its initial intensity, and this "ringdown time" can be used to calculate the concentration of the absorbing substance in the gas mixture in the cavity. | 7 | Physical Chemistry |
In prehistory gold could be found in several areas of Europe; the Carpathian region, Iberia, south-western France, Brittany, Britain and Ireland. The latter in particular had rich gold reserves, and as such has been labelled an "ancient El Dorado". Across the world, and in many cultures, gold has been highly valued as a precious metal, in part because of its rarity and also because of its properties; for instance, unlike copper it is malleable, flexible and homogenous, and can be worked by hammering, rather than having to be worked through casting, annealing or soldering. Any products made from gold do not corrode, but instead have what has been described as an "intrinsic beauty", with many prehistoric peoples probably ascribing gold items a "symbolic as well as a decorative function". | 8 | Metallurgy |
Immunogold labeling was first used in 1971 by Faulk and Taylor to identify Salmonella antigens. It was first applied in transmission electron microscopy (TEM) and was especially useful in highlighting proteins found in low densities, such as some cell surface antigens. As the resolution of scanning electron microscopy (SEM) increased, so too did the need for nanoparticle-sized labels such as immunogold. In 1975, Horisberger and coworkers successfully visualised gold nanoparticles with a diameter of less than 30 nm
and this soon became an established SEM technique. | 1 | Biochemistry |
Andrée Marquet (born 1934), is a French chemist specializing in organic chemistry and chemical biology, professor emeritus at the Pierre and Marie Curie University and correspondent at the French Academy of sciences since 1993. | 0 | Organic Chemistry |
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*Yang, F., Moss, L. G., & Phillips Jr, G. N. (1996). The molecular structure of green fluorescent protein. Nature biotechnology, 14(10), 1246–1251.
*Schotte, F., Lim, M., Jackson, T. A., Smirnov, A. V., Soman, J., Olson, J. S., ... & Anfinrud, P. A. (2003). Watching a protein as it functions with 150-ps time-resolved x-ray crystallography. Science, 300(5627), 1944–1947. | 1 | Biochemistry |
IVF success rates are the percentage of all IVF procedures that result in favourable outcomes. Depending on the type of calculation used, this outcome may represent the number of confirmed pregnancies, called the pregnancy rate, or the number of live births, called the live birth rate. Due to advances in reproductive technology, live birth rates by cycle five of IVF have increased from 76% in 2005 to 80% in 2010, despite a reduction in the number of embryos being transferred (which decreased the multiple birth rate from 25% to 8%).
The success rate depends on variable factors such as age of the birthing person, cause of infertility, embryo status, reproductive history, and lifestyle factors. Younger candidates of IVF are more likely to get pregnant. People older than 41 are more likely to get pregnant with a donor egg. People who have been previously pregnant are in many cases more successful with IVF treatments than those who have never been pregnant. | 1 | Biochemistry |
* Sadideen H, Swaminathan R. (2006): "Macroprolactin: what is it and what is its importance?" Int J Clin Pract. 60(4):457-61. | 1 | Biochemistry |
John Michael Ramsey is an American analytical chemist at the University of North Carolina at Chapel Hill. He currently holds the position of Minnie N. Goldby Distinguished Professor of Chemistry. His current research with the university focuses on microscale and nanoscale devices such as microchip electrospray, microscale Ion trap mass spectrometers, and microfluidic point of care devices. He is ranked #2 in the "Giants of Nano" field on The Analytical Scientist Power List. | 3 | Analytical Chemistry |
Both enantiomers of pseudoephedrine are commercially available. Racemic pseudoephedrine has many medical uses. Because pseudoephedrine can be used to illegally make methamphetamine, the purchase of pseudoephedrine for use in academic or industrial research is rather regulated. As an alternative, Myers et al. reported the utility of pseudoephenamine chiral auxiliaries in alkylation reactions. While pseudoephenamine is not readily available from commercial sources, it can be synthesized with relative ease from benzil and cannot be used to make amphetamines.
Pseudoephedrine amides are typically prepared by acylation with an acyl chloride or anhydride.
<br /> | 4 | Stereochemistry |
The choice of working fluids is known to have a significant impact on the thermodynamic as well as economic performance of the cycle. A suitable fluid must exhibit favorable physical, chemical, environmental, safety and economic properties such as low specific volume (high density), viscosity, toxicity, flammability, ozone depletion potential (ODP), global warming potential (GWP) and cost, as well as favorable process characteristics such as high thermal and exergetic efficiency. These requirements apply both to pure (single-component) and mixed (multicomponent) working fluids. Existing research is largely focused on the selection of pure working fluids, with vast number of published reports currently available. An important restriction of pure working fluids is their constant temperature profile during phase change. Working fluid mixtures are more appealing than pure fluids because their evaporation temperature profile is variable, therefore follows the profile of the heat source better, as opposed to the flat (constant) evaporation profile of pure fluids. This enables an approximately stable temperature difference during evaporation in the heat exchanger, coined as temperature glide, which significantly reduces exergetic losses. Despite their usefulness, recent publications addressing the selection of mixed fluids are considerably fewer.<br>
Many authors like for example O. Badr et al. have suggested the following thermodynamic and physical criteria which a working fluid should meet for heat engines like Rankine cycles. There are some differences in the criteria concerning the working fluids used in heat engines and refrigeration cycles or heat pumps, which are listed below accordingly: | 7 | Physical Chemistry |
The Gallic acid reagent is used as a simple spot-test to presumptively identify drug precursor chemicals. It is composed of a mixture of gallic acid and concentrated sulfuric acid.
0.05 g of gallic acid is used for every 10 mls of sulfuric acid. The same ratio of gallic acid n-propyl ester in sulfuric acid can also be used.
Because of its short shelf life (changing to pale violet color) it is sometimes prepared by dissolving gallic acid into ethanol and adding the sulfuric acid at the time of testing from a separate bottle. In this case 100 mL ethanol is used and one drop of sulfuric acid is used per drop of gallic acid in ethanol. | 3 | Analytical Chemistry |
Genome-wide association studies (GWAS) identify linkages between alleles and observable traits such as phenotypes and diseases. Most of the associations are between single-nucleotide polymorphisms (SNPs) and the trait being examined and most of these SNPs are located in non-functional DNA. The association establishes a linkage that helps map the DNA region responsible for the trait but it does not necessarily identify the mutations causing the disease or phenotypic difference.
SNPs that are tightly linked to traits are the ones most likely to identify a causal mutation. (The association is referred to as tight linkage disequilibrium.) About 12% of these polymorphisms are found in coding regions; about 40% are located in introns; and most of the rest are found in intergenic regions, including regulatory sequences. | 1 | Biochemistry |
Locascio is an interdisciplinary researcher. She worked at NIST for 31 years, rising from a research biomedical engineer to eventually leading the agencys material measurement laboratory. Locascio also served as the acting associate director for laboratory programs, the number two position at NIST, providing direction and operational guidance for NISTs lab research programs across two campuses in Gaithersburg, Maryland, and Boulder, Colorado. She received the 2017 American Chemical Society Earle B. Barnes Award for Leadership in Chemical Research Management, and the 2017 Washington Academy of Sciences Special Award in Scientific Leadership. Locascio has published 115 scientific papers and has received 12 patents in the fields of bioengineering and analytical chemistry. During her time at NIST, she received the Department of Commerce Silver Medal, American Chemical Society Division of Analytical Chemistry Arthur F. Findeis Award, the NIST Safety Award and the NIST Applied Research Award. Locascio is also a fellow of the American Chemical Society and the American Institute for Medical and Biological Engineering.
In late 2017, Locascio joined University of Marylands faculty. She was the first person to serve as the vice president for research of both the College Park and Baltimore campuses. In this role, Locascio oversaw the University of Marylands research and innovation enterprise at these two campuses, which garner a combined $1.1 billion in external research funding each year. Within Locascio's purview was the development of large interdisciplinary research programs, technology commercialization, innovation and economic development efforts, and strategic partnerships with industry, federal, academic, and nonprofit collaborators. She also served as a professor in the Fischell Department of Bioengineering at the A. James Clark School of Engineering with a secondary appointment in the department of pharmacology in the School of Medicine. In 2021, Locascio inducted as a fellow of the National Academy of Inventors. At the University of Maryland that same year, she was succeeded by interim vice president Amitabh Varshney.
On July 16, 2021, President Joe Biden nominated Locascio as the under secretary of commerce for standards and technology. She was confirmed by the Senate on April 7, 2022. On April 19, 2022, Locascio sworn in by U.S. secretary of commerce Gina Raimondo. She is the fourth Under Secretary of Commerce for Standards and Technology and 17th director of NIST. Locascio is the third female head of NIST. | 3 | Analytical Chemistry |
CRP concentrations between 2 and 10 mg/L are considered as metabolic inflammation: metabolic pathways that cause arteriosclerosis and type II diabetes mellitus | 1 | Biochemistry |
Superelectrophiles are defined as cationic electrophilic reagents with greatly enhanced reactivities in the presence of superacids. These compounds were first described by George A. Olah. Superelectrophiles form as a doubly electron deficient superelectrophile by protosolvation of a cationic electrophile. As observed by Olah, a mixture of acetic acid and boron trifluoride is able to remove a hydride ion from isobutane when combined with hydrofluoric acid via the formation of a superacid from BF and HF. The responsible reactive intermediate is the [CHCOH] dication. Likewise, methane can be nitrated to nitromethane with nitronium tetrafluoroborate NOBF only in presence of a strong acid like fluorosulfuric acid via the protonated nitronium dication.
In gitionic (gitonic) superelectrophiles, charged centers are separated by no more than one atom, for example, the protonitronium ion O=N=O—H (a protonated nitronium ion). And, in distonic superelectrophiles, they are separated by 2 or more atoms, for example, in the fluorination reagent F-TEDA-BF. | 7 | Physical Chemistry |
Porphyrin complexes consist of a square planar MN core. The periphery of the porphyrins, consisting of sp-hybridized carbons, generally display small deviations from planarity. "Ruffled" or saddle-shaped porphyrins is attributed to interactions of the system with its environment. Additionally, the metal is often not centered in the N plane. For free porphyrins, the two pyrrole protons are mutually trans and project out of the N plane. These nonplanar distortions are associated with altered chemical and physical properties. Chlorophyll-rings are more distinctly nonplanar, but they are more saturated than porphyrins. | 1 | Biochemistry |
Some bacteria such as enteropathogenic E. coli and enterohemorrhagic E. coli can induce membrane ruffling by secreting toxins via the type three secretion system and modifying the host cytoskeleton. Such toxins include EspT, Map, and SopE, which mimic RhoGEF and activate endogenous Rho GTPases to manipulate actin polymerisation in the infected cell. | 1 | Biochemistry |
Transcription factor 7-like 2 (T-cell specific, HMG-box), also known as TCF7L2 or TCF4, is a protein acting as a transcription factor that, in humans, is encoded by the TCF7L2 gene. The TCF7L2 gene is located on chromosome 10q25.2–q25.3, contains 19 exons. As a member of the TCF family, TCF7L2 can form a bipartite transcription factor and influence several biological pathways, including the Wnt signalling pathway.
Single-nucleotide polymorphisms (SNPs) in this gene are especially known to be linked to higher risk to develop type 2 diabetes, gestational diabetes, multiple neurodevelopmental disorders including schizophrenia and autism spectrum disorder, as well as other diseases. The SNP rs7903146, within the TCF7L2 gene, is, to date, the most significant genetic marker associated with type 2 diabetes risk. | 1 | Biochemistry |
Alternative means of assimilating iron are surface reduction, lowering of pH, utilization of heme, or extraction of protein-complexed metal. Recent data suggest that iron-chelating molecules with similar properties to siderophores, were produced by marine bacteria under phosphate limiting growth condition. In nature phosphate binds to different type of iron minerals, and therefore it was hypothesized that bacteria can use siderophore-like molecules to dissolve such complex in order to access the phosphate. | 1 | Biochemistry |
Monoallelic gene expression (MAE) is the phenomenon of the gene expression, when only one of the two gene copies (alleles) is actively expressed (transcribed), while the other is silent. Diploid organisms bear two homologous copies of each chromosome (one from each parent), a gene can be expressed from both chromosomes (biallelic expression) or from only one (monoallelic expression). MAE can be Random monoallelic expression (RME) or Constitutive monoallelic expression (constitutive). Constitutive monoallelic expression occurs from the same specific allele throughout the whole organism or tissue, as a result of genomic imprinting. RME is a broader class of monoallelic expression, which is defined by random allelic choice in somatic cells, so that different cells of the multi-cellular organism express different alleles. | 1 | Biochemistry |
Vacuum fusion is an analytical chemistry technique, used for determining the oxygen, hydrogen, and sometimes nitrogen content of metals. While ineffective when used on alkali or earth metals, vacuum fusion remains a viable means when applied to almost all other metals. | 3 | Analytical Chemistry |
Amides are usually prepared by coupling a carboxylic acid with an amine. The direct reaction generally requires high temperatures to drive off the water:
Esters are far superior substrates relative to carboxylic acids.
Further "activating" both acid chlorides (Schotten-Baumann reaction) and anhydrides (Lumière–Barbier method) react with amines to give amides:
Peptide synthesis use coupling agents such as HATU, HOBt, or PyBOP. | 0 | Organic Chemistry |
The expression host of choice for the expression of many proteins is Escherichia coli as the production of heterologous protein in E. coli is relatively simple and convenient, as well as being rapid and cheap. A large number of E. coli expression plasmids are also available for a wide variety of needs. Other bacteria used for protein production include Bacillus subtilis.
Most heterologous proteins are expressed in the cytoplasm of E. coli. However, not all proteins formed may be soluble in the cytoplasm, and incorrectly folded proteins formed in cytoplasm can form insoluble aggregates called inclusion bodies. Such insoluble proteins will require refolding, which can be an involved process and may not necessarily produce high yield. Proteins which have disulphide bonds are often not able to fold correctly due to the reducing environment in the cytoplasm which prevents such bond formation, and a possible solution is to target the protein to the periplasmic space by the use of an N-terminal signal sequence. Another possibility is to manipulate the redox environment of the cytoplasm. Other more sophisticated systems are also being developed; such systems may allow for the expression of proteins previously thought impossible in E. coli, such as glycosylated proteins.
The promoters used for these vector are usually based on the promoter of the lac operon or the T7 promoter, and they are normally regulated by the lac operator. These promoters may also be hybrids of different promoters, for example, the Tac-Promoter is a hybrid of trp and lac promoters. Note that most commonly used lac or lac-derived promoters are based on the lacUV5 mutant which is insensitive to catabolite repression. This mutant allows for expression of protein under the control of the lac promoter when the growth medium contains glucose since glucose would inhibit gene expression if wild-type lac promoter is used. Presence of glucose nevertheless may still be used to reduce background expression through residual inhibition in some systems.
Examples of E. coli expression vectors are the pGEX series of vectors where glutathione S-transferase is used as a fusion partner and gene expression is under the control of the tac promoter, and the pET series of vectors which uses a T7 promoter.
It is possible to simultaneously express two or more different proteins in E. coli using different plasmids. However, when 2 or more plasmids are used, each plasmid needs to use a different antibiotic selection as well as a different origin of replication, otherwise one of the plasmids may not be stably maintained. Many commonly used plasmids are based on the ColE1 replicon and are therefore incompatible with each other; in order for a ColE1-based plasmid to coexist with another in the same cell, the other would need to be of a different replicon, e.g. a p15A replicon-based plasmid such as the pACYC series of plasmids. Another approach would be to use a single two-cistron vector or design the coding sequences in tandem as a bi- or poly-cistronic construct. | 1 | Biochemistry |
Transcription attenuation is a type of prokaryotic regulation that happens only under certain conditions. This process occurs at the beginning of RNA transcription and causes the RNA chain to terminate before gene expression. Transcription attenuation is caused by the incorrect formation of a nascent RNA chain. This nascent RNA chain adopts an alternative secondary structure that does not interact appropriately with the RNA polymerase. In order for gene expression to proceed, regulatory proteins must bind to the RNA chain and remove the attenuation, which is costly for the cell.
In prokaryotes there are two mechanisms of transcription attenuation. These two mechanisms are intrinsic termination and factor-dependent termination.
- In the intrinsic termination mechanism, also known as Rho-independent termination, the RNA chain forms a stable transcript hairpin structure at the 3end of the genes that cause the RNA polymerase to stop transcribing. The stem-loop is followed by a run of Us (poly U tail) which stalls the polymerase, so the RNA hairpin have enough time to form. Then, the polymerase is dissociated due to the weak binding between the poly U tail, from the transcript RNA, and the poly A tail, from the DNA template, causing the mRNA to be prematurely released. This process inhibits transcription. To clarify, this mechanism is called Rho-independent because it does not require any additional protein factor as the factor-dependent termination does, which is a simpler mechanism for the cell to regulate gene transcription. Some examples of bacteria where this type of regulation predominates are Neisseria, Psychrobacter and Pasteurellaceae, as well as the majority of bacteria in the Firmicutes phylum.
- In factor-dependent termination, which is a protein factor complex containing Rho factor, is bound to a segment from the RNA chain transcript. The Rho complex then starts looking in the 3 direction for a paused RNA polymerase. If the polymerase is found, the process immediately stops, which results in the abortion of RNA transcription. Even though this system is not as common as the one described above, there are some bacteria that uses this type of termination, such as the tna operon in E.coli'.
This type of regulation is not efficient in eukaryotes because transcription occurs in the nucleus while translation occurs in the cytoplasm. Therefore, the mechanism is not continued and it cannot execute appropriately as it would if both processes happen on the cytoplasm. | 1 | Biochemistry |
The LH 2 is usually bound to photosystem II, but it can undock and bind PS I instead depending on light conditions. This behavior is controlled by reversible phosphorylation. This reaction represents a system for balancing the excitation energy between the two photosystems. | 5 | Photochemistry |
Mass spectrometric immunoassay (MSIA) is a rapid method is used to detect and/ or quantify antigens and or antibody analytes. This method uses an analyte affinity (either through antigens or antibodies) isolation to extract targeted molecules and internal standards from biological fluid in preparation for matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF-MS). This method allows for "top down" and "bottom up" analysis. This sensitive method allows for a new and improved process for detecting multiple antigens and antibodies in a single assay. This assay is also capable of distinguishing mass shifted forms of the same molecule via a panantibody, as well as distinguish point mutations in proteins. Each specific form is detected uniquely based on their characteristic molecular mass. MSIA has dual specificity because of the antibody-antigen reaction coupled with the power of a mass spectrometer.
There are various other immunoassy techniques that have been used previously such as radioimmunoassay (RIA) and enzyme immunoassay (EIA and ELISA). These techniques are extremely sensitive however, there are many limitations to these methods. For example, quantification for ELISA and EIA require several hours because the binding has to reach equilibrium. RIA's disadvantage is that you need radioactive particles which are universally known to be carcinogens.
The creation of MSIA fulfilled the need to determine the presence of one or more antigens in a specimen as well as the quantification of those said species. | 1 | Biochemistry |
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