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Methylotrophs are a diverse group of microorganisms that can use reduced one-carbon compounds, such as methanol or methane, as the carbon source for their growth; and multi-carbon compounds that contain no carbon-carbon bonds, such as dimethyl ether and dimethylamine. This group of microorganisms also includes those capable of assimilating reduced one-carbon compounds by way of carbon dioxide using the ribulose bisphosphate pathway. These organisms should not be confused with methanogens which on the contrary produce methane as a by-product from various one-carbon compounds such as carbon dioxide.
Some methylotrophs can degrade the greenhouse gas methane, and in this case they are called methanotrophs. The abundance, purity, and low price of methanol compared to commonly used sugars make methylotrophs competent organisms for production of amino acids, vitamins, recombinant proteins, single-cell proteins, co-enzymes and cytochromes. | 0 | Organic Chemistry |
The hydration reaction of sulfuric acid is highly exothermic, dilution.
As indicated by its acid dissociation constant, sulfuric acid is a strong acid:
: K = 1000 (pK = −3)
The product of this ionization is , the bisulfate anion. Bisulfate is a far weaker acid:
: K = 0.01 (pK = 2)
The product of this second dissociation is , the sulfate anion. | 7 | Physical Chemistry |
For water at standard temperature (25 C) the net cell reaction may be written:
Using Gibbs potentials ( kJ/mol), the thermodynamic voltage at standard conditions is
: 1.229 Volt (2 electrons needed to form H(g))
Just as the combustion of hydrogen and oxygen generates heat, the reverse reaction generating hydrogen and oxygen will absorb heat. The thermoneutral voltage is (using kJ/mol):
: 1.481 Volts. | 7 | Physical Chemistry |
The definition employed by Lieb and Yngvason is rather different since the state changes considered can be the result of arbitrarily complicated, possibly violent, irreversible processes and there is no mention of heat or differential forms. In the example of the water given above, if the stirring is done slowly, the transition from cool water to warm water will be quasistatic. However, a system containing an exploded firecracker is adiabatically accessible from a system containing an unexploded firecracker (but not vice versa), and this transition is far from quasistatic. Lieb and Yngvasons definition of adiabatic accessibility is: A state is adiabatically accessible from a state , in symbols (pronounced X precedes' Y), if it is possible to transform into in such a way that the only net effect of the process on the surroundings is that a weight has been raised or lowered (or a spring is stretched/compressed, or a flywheel is set in motion). | 7 | Physical Chemistry |
Acid Base Accounting (ABA), namely, the practice of quantifying sources of acidity and alkalinity, is a critical aspect of managing acid sulfate soils. For example, ABA is used to calculate the amount of neutralising agent (e.g., lime) required to neutralise stockpiled sulfidic material generated from excavation or dredging activities.
The standard Australian ABA system describes three operationally defined pools of acidity (mol H per tonne dry soil).
Potential Sulfidic Acidity (PSA) is a measure of the ‘oxidisable sulfur’ associated with Reduced Inorganic Sulfur (RIS) (e.g., iron sulfides and elemental sulfur) that may oxidise to produce sulfuric acid.
Titratable Actual Acidity (TAA) is a measure of soluble and exchangeable acidity associated with organic acids and loosely bound Al and Fe ions – which react with water to produce H (i.e., hydrolysis).
Retained Acidity (RA) is a measure of sparingly soluble sulfates such as [https://www.mindat.org/min-2078.html jarosite] and [https://www.mindat.org/min-7281.html schwertmannite], which slowly generate acidity via the release and hydrolysis of Al and Fe.
The Acid Neutralising Capacity (ANC) of the soil sample is subtracted from the sum of the PSA, TAA and RA to calculate the net acidity. ANC is typically associated with carbonates and, to a lesser extent, organic matter.
In Australia, net acidity is used in combination with the texture or clay content of the sample and the weight of acid sulfate soil to be disturbed (e.g., excavated for construction) to determine whether or not an Acid Sulfate Soil Management Plan (ASSMP) is required as part of statutory environmental management protocols. | 9 | Geochemistry |
Inductively, the negatively charged carboxylate ion moderately repels the electrons in the bond attaching it to the ring. Thus, there is a weak electron-donating +I effect. There is an almost zero -M effect since the electron-withdrawing resonance capacity of the carbonyl group is effectively removed by the delocalisation of the negative charge of the anion on the oxygen. Thus overall the carboxylate group (unlike the carboxyl group) has an activating influence. | 0 | Organic Chemistry |
Cancer cells lack or have reduced ferrochelatase activity and this results in accumulation of Protoporphyrin IX, a fluorescent substance that can easily be visualized. | 1 | Biochemistry |
Human genes encoding heterogeneous nuclear ribonucleoproteins include:
* HNRNPA0, HNRNPA1, HNRNPA1L1, HNRNPA1L2, HNRNPA3, HNRNPA2B1
* HNRNPAB
* HNRNPB1
* HNRNPC, HNRNPCL1
* HNRNPD (AUF1), HNRPDL
* HNRNPF
* HNRNPG (RBMX)
* HNRNPH1, HNRNPH2, HNRNPH3
* HNRNPI (PTB)
* HNRNPK
* HNRNPL, HNRPLL
* HNRNPM
* HNRNPP2 (FUS/TLS)
* HNRNPR
* HNRNPQ (SYNCRIP)
* HNRNPU, HNRNPUL1, HNRNPUL2, HNRNPUL3
* FMR1 | 1 | Biochemistry |
Systems have been developed to create transgenic organisms in a wide variety of other animals. Chickens have been genetically modified for a variety of purposes. This includes studying embryo development, preventing the transmission of bird flu and providing evolutionary insights using reverse engineering to recreate dinosaur-like phenotypes. A GM chicken that produces the drug Kanuma, an enzyme that treats a rare condition, in its egg passed US regulatory approval in 2015. Genetically modified frogs, in particular Xenopus laevis and Xenopus tropicalis, are used in developmental biology research. GM frogs can also be used as pollution sensors, especially for endocrine disrupting chemicals. There are proposals to use genetic engineering to control cane toads in Australia.
The nematode Caenorhabditis elegans is one of the major model organisms for researching molecular biology. RNA interference (RNAi) was discovered in C. elegans and could be induced by simply feeding them bacteria modified to express double stranded RNA. It is also relatively easy to produce stable transgenic nematodes and this along with RNAi are the major tools used in studying their genes. The most common use of transgenic nematodes has been studying gene expression and localization by attaching reporter genes. Transgenes can also be combined with RNAi techniques to rescue phenotypes, study gene function, image cell development in real time or control expression for different tissues or developmental stages. Transgenic nematodes have been used to study viruses, toxicology, diseases, and to detect environmental pollutants.
The gene responsible for albinism in sea cucumbers has been found and used to engineer white sea cucumbers, a rare delicacy. The technology also opens the way to investigate the genes responsible for some of the cucumbers more unusual traits, including hibernating in summer, eviscerating their intestines, and dissolving their bodies upon death. Flatworms have the ability to regenerate themselves from a single cell. Until 2017 there was no effective way to transform them, which hampered research. By using microinjection and radiation scientists have now created the first genetically modified flatworms. The bristle worm, a marine annelid, has been modified. It is of interest due to its reproductive cycle being synchronized with lunar phases, regeneration capacity and slow evolution rate. Cnidaria such as Hydra and the sea anemone Nematostella vectensis are attractive model organisms to study the evolution of immunity and certain developmental processes. Other animals that have been genetically modified include snails, geckos, turtles, crayfish, oysters, shrimp, clams, abalone and sponges. | 1 | Biochemistry |
The zincblende structure is similar to the diamond structure except that it is a compound of two distinct interpenetrating fcc lattices, rather than all the same element. Denoting the two elements in the compound by and , the resulting structure factor is | 3 | Analytical Chemistry |
Starting as lecturer at Rivers State University in food chemistry/biochemistry, food process technology, safety and fermentation, toxicology and nutrition in 1975, he has remained there to-date. He is also a researcher in Rivers State University, Port Harcourt (formerly Rivers State University of Science and Technology) and research is mostly centered on the composition and quality evaluation of Nigerian local foodstuff.
As of 2021, Achinewhu serves as professor emeritus at the Rivers State University.
Prior to being appointed vice-chancellor of Rivers State University 2000, Achinewhu held the following positions:
* Dean, Post Graduate School (1998-2000)
* Head of the Department of Food Science & Technology (November 1995 – June 1998)
* Dean, Faculty of Agriculture (1989-1994)
* Director, Rivers Institute of Agricultural Research & Training (RIART), Rivers State University (1986-1989) | 1 | Biochemistry |
Caseins are a family of phosphoproteins (αS1, αS2, β, κ) that account for nearly 80% of bovine milk proteins and that form soluble aggregates are known as "casein micelles" in which κ-casein molecules stabilize the structure. There are several models that account for the spatial conformation of casein in the micelles. One of them proposes that the micellar nucleus is formed by several submicelles, the periphery consisting of microvillosities of κ-casein Another model suggests that the nucleus is formed by casein-interlinked fibrils. Finally, the most recent model proposes a double link among the caseins for gelling to take place. All 3 models consider micelles as colloidal particles formed by casein aggregates wrapped up in soluble κ-casein molecules.
Milk-clotting proteases act on the soluble portion, κ-casein, thus originating an unstable micellar state that
results in clot formation. | 1 | Biochemistry |
HO masers, a type of astrophysical maser, were the first masers to be discovered in space and have been observed in more environments than any other type of maser.
In the Milky Way, HO masers are found in stellar masers (evolved stars), interstellar masers (regions of massive star formation), or in the interface between supernova remnants and molecular material. Interstellar HO masers are often observed from molecular material surrounding ultracompact H II regions (UC H II). But there are masers associated with very young stars that have yet to create UC H II regions. This class of HO masers appears to form near the edges of very dense material, places where HO masers form, and where total densities drop rapidly, and UV radiation from young stars can dissociate the HO molecules. So, observations of HO masers in these regions, can be an important way to probe the distribution of the important HO molecule in interstellar shocks at high spatial resolutions.
Application in water purification
Hydroxyl radicals also play a key role in the oxidative destruction of organic pollutants. | 2 | Environmental Chemistry |
Transmetalation is often used as a step in the catalytic cycles of cross-coupling reactions. Some of the cross-coupling reactions that include a transmetalation step are Stille cross-coupling, Suzuki cross-coupling, Sonogashira cross-coupling, and Negishi cross-coupling. The most useful cross-coupling catalysts tend to be ones that contain palladium. Cross-coupling reactions have the general form of R′–X + M–R → R′–R + M–X and are used to form C–C bonds. R and R′ can be any carbon fragment. The identity of the metal, M, depends on which cross-coupling reaction is being used. Stille reactions use tin, Suzuki reactions use boron, Sonogashira reactions use copper, and Negishi reactions use zinc. The transmetalation step in palladium catalyzed reactions involve the addition of an R–M compound to produce an R′–Pd–R compound. Cross-coupling reactions have a wide range of applications in synthetic chemistry including the area of medicinal chemistry. The Stille reaction has been used to make an antitumor agent, (±)-epi-jatrophone; the Suzuki reaction has been used to make an antitumor agent, oximidine II; the Sonogashira reaction has been used to make an anticancer drug, eniluracil; and the Negishi reaction has been used to make the carotenoid β-carotene via a transmetalation cascade. | 0 | Organic Chemistry |
* The mass-market application of microchannel plates is in image intensifier tubes of night vision goggles, which amplify visible and invisible light to make dark surroundings visible to the human eye.
* A 1 GHz real-time display CRT for an analog oscilloscope (the Tektronix 7104) used a microchannel plate placed behind the phosphor screen to intensify the image. Without the plate, the image would be excessively dim, because of the electron-optical design.
* MCP detectors are often employed in instrumentation for physical research, and they can be found in devices such as electron and mass spectrometers. | 7 | Physical Chemistry |
Vibrational spectroscopy provides the most widely used means for characterizing ion associates. Both infrared spectroscopy and Raman spectroscopy have been used. Anions containing a CN group, such as cyanide, cyanate and thiocyanide have a vibration frequency a little above 2000 cm, which can be easily observed, as the spectra of most solvents (other than nitriles) are weak in this region. The anion vibration frequency is "shifted" on formation of ion pairs and other associates, and the extent of the shift gives information about the nature of the species. Other monovalent anions that have been studied include nitrate, nitrite and azide. Ion pairs of monatomic anions, such as halide ions, cannot be studied by this technique. Standard NMR spectroscopy is not very useful, as association/dissociation reactions tend to be fast on the NMR time scale, giving time-averaged signals of the cation and/or anion. However, diffusion ordered spectroscopy (DOSY), with which the sample tube is not spinning, can be used as ion pairs diffuse more slowly than do single ions due to their greater size.
Nearly the same shift of vibration frequency is observed for solvent-shared ion pairs of LiCN, Be(CN) and Al(CN) in liquid ammonia. The extent of this type of ion pairing decreases as the size of the cation increases. Thus, solvent-shared ion pairs are characterized by a rather small shift of vibration frequency with respect to the "free" solvated anion, and the value of the shift is not strongly dependent on the nature of the cation. The shift for contact ion pairs is, by contrast, strongly dependent on the nature of the cation and decreases linearly with the ratio of the cations charge to the squared radius:
:Cs > Rb > K > Na > Li;
:Ba > Sr > Ca.
The extent of contact ion pairing can be estimated from the relative intensities of the bands due to the ion pair and free ion. It is greater with the larger cations. This is counter to the trend expected if coulombic energy were the determining factor. Instead, the formation of a contact ion pair is seen to depend more on the energy needed to displace a solvent molecule from the primary solvation sphere of the cation. This energy decreases with the size of the cation, making ion pairing occur to a greater extent with the larger cations. The trend may be different in other solvents.
Higher ion aggregates, sometimes triples MXM, sometimes dimers of ion pairs (MX), or even larger species can be identified in the Raman spectra of some liquid-ammonia solutions of Na salts by the presence of bands that cannot be attributed to either contact- or solvent-shared ion pairs.
Evidence for the existence of fully solvated ion pairs in solution is mostly indirect, as the spectroscopic properties of such ion pairs are indistinguishable from those of the individual ions. Much of the evidence is based on the interpretation of conductivity measurements. | 7 | Physical Chemistry |
In 1999, the Dioxin Affair occurred when 50 kg of PCB transformer oils were added to a stock of recycled fat used for the production of 500 tonnes of animal feed, eventually affecting around 2,500 farms in several countries. The name Dioxin Affair was coined from early misdiagnosis of dioxins as the primary contaminants, when in fact they turned out to be a relatively small part of the contamination caused by thermal reactions of PCBs. The PCB congener pattern suggested the contamination was from a mixture of Aroclor 1260 and 1254. Over 9 million chickens, and 60,000 pigs were destroyed because of the contamination. The extent of human health effects has been debated, in part because of the use of differing risk assessment methods. One group predicted increased cancer rates, and increased rates of neurological problems in those exposed as neonates. A second study suggested carcinogenic effects were unlikely and that the primary risk would be associated with developmental effects due to exposure in pregnancy and neonates. Two businessmen who knowingly sold the contaminated feed ingredient received two-year suspended sentences for their role in the crisis. | 2 | Environmental Chemistry |
The storage of seeds in a temperature and moisture controlled environment. This technique is used for taxa with orthodox seeds that tolerate desiccation. Seed bank facilities vary from sealed boxes to climate controlled walk-in freezers or vaults. Taxa with recalcitrant seeds that do not tolerate desiccation are typically not held in seed banks for extended periods of time. | 1 | Biochemistry |
The first zinc(I) dimer was isolated in 2004, with more being synthesized in subsequent years. The chemical similarities between magnesium and zinc led researchers to believe that a Mg(I) dimer could then be achieved. With a calculated stability of Mg—Mg bonded dimers, a synthesis route was needed. | 7 | Physical Chemistry |
Studying the decomposition of double salts of aryldiazonium halides with mercury halides by copper powder, in 1929 Nesmeyanov proposed a new method for obtaining arylmercury halides. Later, the diazo method was extended to the synthesis of organometallic compounds of thallium, germanium, tin, lead, arsenic, antimony, and bismuth. The features of the diazo method, which distinguish it from direct metalation methods, are the possibility of obtaining organometallic compounds with different functional groups in the carbon radical and the possibility of selectively introducing a metal atom into a certain position. In 1935 – 1948, Nesmeyanov, together with K. A. Kocheshkov, obtained organic derivatives of tin, lead, antimony and other metals. Due to mutual transitions from organic derivatives of some elements to organic compounds of other elements, organometallic compounds obtained by the diazo method have found new applications in synthesis. | 0 | Organic Chemistry |
Many electrophiles are chiral and optically stable. Typically chiral electrophiles are also optically pure.
One such reagent is the fructose-derived organocatalyst used in the Shi epoxidation. The catalyst can accomplish highly enantioselective epoxidations of trans-disubstituted and trisubstituted alkenes. The Shi catalyst, a ketone, is oxidized by stoichiometric oxone to the active dioxirane form before proceeding in the catalytic cycle.
Oxaziridines such as chiral N-sulfonyloxaziridines effect enantioselective ketone alpha oxidation en route to the AB-ring segments of various natural products, including γ-rhodomycionone and α-citromycinone.
Polymer-bound chiral selenium electrophiles effect asymmetric selenenylation reactions. The reagents are aryl selenenyl bromides, and they were first developed for solution phase chemistry and then modified for solid phase bead attachment via an aryloxy moiety. The solid-phase reagents were applied toward the selenenylation of various alkenes with good enantioselectivities. The products can be cleaved from the solid support using organotin hydride reducing agents. Solid-supported reagents offers advantages over solution phase chemistry due to the ease of workup and purification. | 7 | Physical Chemistry |
TMSCl is reactive toward nucleophiles, resulting in the replacement of the chloride. In a characteristic reaction of TMSCl, the nucleophile is water, resulting in hydrolysis to give the hexamethyldisiloxane:
The related reaction of trimethylsilyl chloride with alcohols can be exploited to produce anhydrous solutions of hydrochloric acid in alcohols, which find use in the mild synthesis of esters from carboxylic acids and nitriles as well as, acetals from ketones. Similarly, trimethylsilyl chloride is also used to silanize laboratory glassware, making the surfaces more lipophilic. | 0 | Organic Chemistry |
RNA editing (also RNA modification) is a molecular process through which some cells can make discrete changes to specific nucleotide sequences within an RNA molecule after it has been generated by RNA polymerase. It occurs in all living organisms and is one of the most evolutionarily conserved properties of RNAs. RNA editing may include the insertion, deletion, and base substitution of nucleotides within the RNA molecule. RNA editing is relatively rare, with common forms of RNA processing (e.g. splicing, 5-capping, and 3-polyadenylation) not usually considered as editing. It can affect the activity, localization as well as stability of RNAs, and has been linked with human diseases.
RNA editing has been observed in some tRNA, rRNA, mRNA, or miRNA molecules of eukaryotes and their viruses, archaea, and prokaryotes. RNA editing occurs in the cell nucleus, as well as within mitochondria and plastids. In vertebrates, editing is rare and usually consists of a small number of changes to the sequence of the affected molecules. In other organisms, such as squids, extensive editing (pan-editing) can occur; in some cases the majority of nucleotides in an mRNA sequence may result from editing. More than 160 types of RNA modifications have been described so far.
RNA-editing processes show great molecular diversity, and some appear to be evolutionarily recent acquisitions that arose independently. The diversity of RNA editing phenomena includes nucleobase modifications such as cytidine (C) to uridine (U) and adenosine (A) to inosine (I) deaminations, as well as non-template nucleotide additions and insertions. RNA editing in mRNAs effectively alters the amino acid sequence of the encoded protein so that it differs from that predicted by the genomic DNA sequence. | 1 | Biochemistry |
The roots of the term absorbance are in the Beer–Lambert law. As light moves through a medium, it will become dimmer as it is being "extinguished". Bouguer recognized that this extinction (now often called attenuation) was not linear with distance traveled through the medium, but related by what we now refer to as an exponential function.
If is the intensity of the light at the beginning of the travel and is the intensity of the light detected after travel of a distance the fraction transmitted, is given by
where is called an attenuation constant (a term used in various fields where a signal is transmitted though a medium) or coefficient. The amount of light transmitted is falling off exponentially with distance. Taking the natural logarithm in the above equation, we get
For scattering media, the constant is often divided into two parts, separating it into a scattering coefficient and an absorption coefficient obtaining
If a size of a detector is very small compared to the distance traveled by the light, any light that is scattered by a particle, either in the forward or backward direction, will not strike the detector. (Bouguer was studying astronomical phenomena, so this condition was met.) In such case, a plot of as a function of wavelength will yield a superposition of the effects of absorption and scatter. Because the absorption portion is more distinct and tends to ride on a background of the scatter portion, it is often used to identify and quantify the absorbing species. Consequently, this is often referred to as absorption spectroscopy, and the plotted quantity is called "absorbance", symbolized as Some disciplines by convention use decadic (base 10) absorbance rather than Napierian (natural) absorbance, resulting in: (with the subscript 10 usually not shown). | 7 | Physical Chemistry |
Antifreeze proteins (AFPs) or ice structuring proteins refer to a class of polypeptides produced by certain animals, plants, fungi and bacteria that permit their survival in temperatures below the freezing point of water. AFPs bind to small ice crystals to inhibit the growth and recrystallization of ice that would otherwise be fatal. There is also increasing evidence that AFPs interact with mammalian cell membranes to protect them from cold damage. This work suggests the involvement of AFPs in cold acclimatization. | 1 | Biochemistry |
Compared to both healthy volunteers and subjects with hypothyroidism and hyperthyroidism, SPINA-GD is reduced in subacute thyroiditis. In this condition, it has a higher specificity, positive and negative likelihood ratio than serum concentrations of thyrotropin, free T4 or free T3. These measures of diagnostic utility are also high in nodular goitre, where SPINA-GD is elevated. Among subjects with subclinical thyrotoxicosis, calculated deiodinase activity is significantly lower in exogenous thyrotoxicosis (resulting from therapy with levothyroxine) than in true hyperthyroidism (ensuing from toxic adenoma, toxic multinodular goitre or Graves' disease). SPINA-GD may therefore be an effective biomarker for the differential diagnosis of thyrotoxicosis.
Compared to healthy subjects, SPINA-GD is significantly reduced in euthyroid sick syndrome. | 1 | Biochemistry |
Excavations from sites where Indus Valley civilisation once flourished reveal usage of bronze for various purposes. Earliest known usage of bronze for art form can be traced back to 2500 BC. Dancing Girl of Mohenjo Daro is attributed for the same. Archaeologists working on excavation site at Kosambi in Uttar Pradesh unearthed a bronze figure of a Girl riding two bulls which is dated approximately between 2000 - 1750 BC further reveals the usage of bronze for casting into an art form during the Late Harappan period. Another such instance of a Late Harappan period bronze artifact was found at Daimbad in Maharashtra suggesting a possibility of a more widespread usage of bronze then localised to places around Indus Valley alone.
Bronze continued to be used as a metal for various statues and statuettes during Classical Period as can be seen from the Bronze hoard discovered in Chausa Bihar, which consisted of bronze statuettes dating between 2nd BC to 6th Century AD.
Bronze art picked up in South India during the Middle Ages during the rule of Pallava's, 8th Century Ardhaparyanka asana icon of Shiva is one notable artifact from this period. Bronze sculpting however peaked during the reign of Cholas (c. 850 CE - 1250 CE). Many of the bronze sculptures from this period are now present in various museums around the world. Nataraja statue found in the Metropolitan Museum of Art, New York City is a remarkable piece of sculpting from this period. | 8 | Metallurgy |
In molecular biology, RNA polymerase (abbreviated RNAP or RNApol), or more specifically DNA-directed/dependent RNA polymerase (DdRP), is an enzyme that catalyzes the chemical reactions that synthesize RNA from a DNA template.
Using the enzyme helicase, RNAP locally opens the double-stranded DNA so that one strand of the exposed nucleotides can be used as a template for the synthesis of RNA, a process called transcription. A transcription factor and its associated transcription mediator complex must be attached to a DNA binding site called a promoter region before RNAP can initiate the DNA unwinding at that position. RNAP not only initiates RNA transcription, it also guides the nucleotides into position, facilitates attachment and elongation, has intrinsic proofreading and replacement capabilities, and termination recognition capability. In eukaryotes, RNAP can build chains as long as 2.4 million nucleotides.
RNAP produces RNA that, functionally, is either for protein coding, i.e. messenger RNA (mRNA); or non-coding (so-called "RNA genes"). Examples of four functional types of RNA genes are:
; Transfer RNA (tRNA): Transfers specific amino acids to growing polypeptide chains at the ribosomal site of protein synthesis during translation;
; Ribosomal RNA (rRNA): Incorporates into ribosomes;
; Micro RNA (miRNA): Regulates gene activity; and, RNA silencing
; Catalytic RNA (ribozyme): Functions as an enzymatically active RNA molecule.
RNA polymerase is essential to life, and is found in all living organisms and many viruses. Depending on the organism, a RNA polymerase can be a protein complex (multi-subunit RNAP) or only consist of one subunit (single-subunit RNAP, ssRNAP), each representing an independent lineage. The former is found in bacteria, archaea, and eukaryotes alike, sharing a similar core structure and mechanism. The latter is found in phages as well as eukaryotic chloroplasts and mitochondria, and is related to modern DNA polymerases. Eukaryotic and archaeal RNAPs have more subunits than bacterial ones do, and are controlled differently.
Bacteria and archaea only have one RNA polymerase. Eukaryotes have multiple types of nuclear RNAP, each responsible for synthesis of a distinct subset of RNA: | 1 | Biochemistry |
The desalinated water is stabilized to protect downstream pipelines and storage, usually by adding lime or caustic soda to prevent corrosion of concrete-lined surfaces. Liming material is used to adjust pH between 6.8 and 8.1 to meet the potable water specifications, primarily for effective disinfection and for corrosion control. Remineralisation may be needed to replace minerals removed from the water by desalination, although this process has proved to be costly and inconvenient in order to meet mineral demand by humans and plants as found in typical freshwater. For instance water from Israels national water carrier typically contains dissolved magnesium levels of 20 to 25 mg/liter, while water from the Ashkelon plant has no magnesium. Ashkelon water created magnesium-deficiency symptoms in crops, including tomatoes, basil, and flowers, and had to be remedied by fertilization. Israeli drinking water standards require a minimum calcium level of 20 mg/liter. Askelons post-desalination treatment uses sulfuric acid to dissolve calcite (limestone), resulting in calcium concentrations of 40 to 46 mg/liter, lower than the 45 to 60 mg/liter found in typical Israeli fresh water. | 3 | Analytical Chemistry |
In 1940, ZoBell and Conn stated that they had never encountered "true psychrophiles" or organisms that grow best at relatively low temperatures. In 1958, J. L. Ingraham supported this by concluding that there are very few or possibly no bacteria that fit the textbook definitions of psychrophiles. Richard Y. Morita emphasizes this by using the term psychrotroph to describe organisms that do not meet the definition of psychrophiles. The confusion between the terms psychrotrophs and psychrophiles was started because investigators were unaware of the thermolability of psychrophilic organisms at the laboratory temperatures. Due to this, early investigators did not determine the cardinal temperatures for their isolates.
The similarity between these two is that they are both capable of growing at zero, but optimum and upper temperature limits for the growth are lower for psychrophiles compared to psychrotrophs. Psychrophiles are also more often isolated from permanently cold habitats compared to psychrotrophs. Although psychrophilic enzymes remain under-used because the cost of production and processing at low temperatures is higher than for the commercial enzymes that are presently in use, the attention and resurgence of research interest in psychrophiles and psychrotrophs will be a contributor to the betterment of the environment and the desire to conserve energy. | 1 | Biochemistry |
Cyclamin is an irritant compound that causes gastroenteritis, bloody stools, dizziness, seizures and even death by asphyxiation. Studied by many physiologists, cyclamin was viewed merely as a local irritant. However, considering the toxic effects of cyclamin, this a misconception. The roots and bulbs of cyclamen plants containing cyclamin are known to cause severe diarrhea, nausea, vomiting and even death if eaten raw. | 0 | Organic Chemistry |
In molecular biology, the protein domain S-adenosylmethionine synthetase, C-terminal domain refers to the C terminus of the S-adenosylmethionine synthetase | 1 | Biochemistry |
Bilbao Crystallographic Server is an open access website offering online crystallographic database and programs aimed at analyzing, calculating and visualizing problems of structural and mathematical crystallography, solid state physics and structural chemistry. Initiated in 1997 by the Materials Laboratory of the Department of Condensed Matter Physics at the University of the Basque Country, Bilbao, Spain, the Bilbao Crystallographic Server is developed and maintained by academics. | 3 | Analytical Chemistry |
PTEN is a tumor suppressor that inhibits the PI3K/AKT pathway. PTEN inhibitors, such as bisperoxovanadium, can enhance the PI3K/AKT pathway to promote cell migration, survival and proliferation. While there are some concerns over possible cell cycle dysregulation and tumorigenesis, temporary and moderate PTEN inhibition may confer neuroprotection against traumatic brain injury and improve CNS recovery by reestablishing lost connections by axonogenesis. Medicinal value of PTEN inhibitors remains to be determined. | 1 | Biochemistry |
These drugs fall into two groups:
*Non-depolarizing blocking agents: These agents constitute the majority of the clinically relevant neuromuscular blockers. They act by competitively blocking the binding of ACh to its receptors, and in some cases, they also directly block the ionotropic activity of the ACh receptors.
*Depolarizing blocking agents: These agents act by depolarizing the sarcolemma of the skeletal muscle fiber. This persistent depolarization makes the muscle fiber resistant to further stimulation by ACh. | 1 | Biochemistry |
The overall process is as follows:
A primer that matches the beginning of the DNA to sequence is used to synthesize a short DNA strand adjacent to the unknown sequence, starting with the primer (see PCR).
The new short DNA strand is sequenced using the chain termination method.
The end of the sequenced strand is used as a primer for the next part of the long DNA sequence, hence the term "walking".
The method can be used to sequence entire chromosomes (hence "chromosome walking"). Primer walking was also the basis for the development of shotgun sequencing, which uses random primers instead of specifically chosen ones. | 1 | Biochemistry |
This style is traditional to suburbs of Philadelphia, Pennsylvania, including Chester, Bucks, and Montgomery Counties. The amount of the required offset is divided evenly between the hinge and the pintle. | 8 | Metallurgy |
All metals can be classified into a galvanic series representing the electrical potential they develop in a given electrolyte against a standard reference electrode. The relative position of two metals on such a series gives a good indication of which metal is more likely to corrode more quickly. However, other factors such as water aeration and flow rate can influence the rate of the process markedly. | 8 | Metallurgy |
Cellulose is a polyol and thus susceptible to acetylation, which is achieved using acetic anhydride. Acetylation disrupts hydrogen bonding, which otherwise dominates the properties of cellulose. Consequently, the cellulose esters are soluble in organic solvents and can be cast into fibers and films. | 0 | Organic Chemistry |
In Thomson scattering a charged particle emits radiation under incident light. The particle may be an ordinary atomic electron, so emission coefficients have practical applications.
If is the energy scattered by a volume element into solid angle between wavelengths and per unit time then the Emission coefficient is .
The values of in Thomson scattering can be predicted from incident flux, the density of the charged particles and their Thomson differential cross section (area/solid angle). | 7 | Physical Chemistry |
The Mg ion tends to bind only weakly to proteins (K ≤ 10) and this can be exploited by the cell to switch enzymatic activity on and off by changes in the local concentration of Mg. Although the concentration of free cytoplasmic Mg is on the order of 1 mmol/L, the total Mg content of animal cells is 30 mmol/L and in plants the content of leaf endodermal cells has been measured at values as high as 100 mmol/L (Stelzer et al., 1990), much of which buffered in storage compartments. The cytoplasmic concentration of free Mg is buffered by binding to chelators (e.g., ATP), but also, what is more important, it is buffered by storage of Mg in intracellular compartments. The transport of Mg between intracellular compartments may be a major part of regulating enzyme activity. The interaction of Mg with proteins must also be considered for the transport of the ion across biological membranes. | 1 | Biochemistry |
A glycocalyx can also be found on the apical portion of microvilli within the digestive tract, especially within the small intestine. It creates a meshwork 0.3 μm thick and consists of acidic mucopolysaccharides and glycoproteins that project from the apical plasma membrane of epithelial absorptive cells. It provides additional surface for adsorption and includes enzymes secreted by the absorptive cells that are essential for the final steps of digestion of proteins and sugars. | 1 | Biochemistry |
Photographic film responds to ultraviolet radiation but the glass lenses of cameras usually block radiation shorter than 350 nm. Slightly yellow UV-blocking filters are often used for outdoor photography to prevent unwanted bluing and overexposure by UV rays. For photography in the near UV, special filters may be used. Photography with wavelengths shorter than 350 nm requires special quartz lenses which do not absorb the radiation.
Digital cameras sensors may have internal filters that block UV to improve color rendition accuracy. Sometimes these internal filters can be removed, or they may be absent, and an external visible-light filter prepares the camera for near-UV photography. A few cameras are designed for use in the UV.
Photography by reflected ultraviolet radiation is useful for medical, scientific, and forensic investigations, in applications as widespread as detecting bruising of skin, alterations of documents, or restoration work on paintings. Photography of the fluorescence produced by ultraviolet illumination uses visible wavelengths of light.
In ultraviolet astronomy, measurements are used to discern the chemical composition of the interstellar medium, and the temperature and composition of stars. Because the ozone layer blocks many UV frequencies from reaching telescopes on the surface of the Earth, most UV observations are made from space. | 5 | Photochemistry |
Carbenes had first been postulated by Eduard Buchner in 1903 in cyclopropanation studies of ethyl diazoacetate with toluene. In 1912 Hermann Staudinger also converted alkenes to cyclopropanes with diazomethane and CH as an intermediate. Doering in 1954 demonstrated their synthetic utility with dichlorocarbene. | 0 | Organic Chemistry |
This argument for formation of mesocrystals requires only a confined space that the reaction takes place in. As the nanoparticle grow into crystals, they have no choice but to align with each other in such a confined space. | 7 | Physical Chemistry |
Before analyzing target genome structural aberration and copy number variation (CNV) with ESP, the target genome is usually amplified and conserved with artificial chromosome construction. The classic strategy to construct an artificial chromosome is bacterial artificial chromosome (BAC). Basically, the target chromosome is randomly digested and inserted into plasmids which are transformed and cloned in bacteria. The size of fragments inserted is 150–350 kb. Another commonly used artificial chromosome is fosmid. The difference between BAC and fosmids is the size of the DNA inserted. Fosmids can only hold 40 kb DNA fragments, which allows a more accurate breakpoint determination. | 1 | Biochemistry |
This work also explains why genomes such as the human genome have billions of bases, and why only a small fraction (~2%) codes for proteins and other regulatory elements. If split genes originated from random primordial DNA sequences, they would contain a significant amount of DNA that represented by introns. Furthermore, a genome assembled from random DNA containing split genes would also include intergenic random DNA. Thus, genomes that originated from random DNA sequences had to be large, regardless of the complexity of the organism.
The observation that several organisms such as the onion (~16 billion bases) and salamander (~32 billion bases) have much larger genomes than humans (~3 billion bases) while the organisms are no more complex than humans comports with the theory. Furthermore, the fact that several organisms with smaller genomes have a similar number of genes as human, such as C. elegans (genome size ~100 million bases, ~19,000 genes) and Arabidopsis thaliana (genome size ~125 million bases, ~25,000 genes), supports the theory. The theory predicts that the introns in the split genes in these genomes could be the “reduced” (or deleted) form compared to larger genes with long introns, thus leading to reduced genomes. In fact, researchers have recently proposed that these smaller genomes are actually reduced genomes. | 1 | Biochemistry |
Many microorganisms living in sea ice possess AFPs that belong to a single family. The diatoms Fragilariopsis cylindrus and F. curta play a key role in polar sea ice communities, dominating the assemblages of both platelet layer and within pack ice. AFPs are widespread in these species, and the presence of AFP genes as a multigene family indicates the importance of this group for the genus Fragilariopsis. AFPs identified in F. cylindrus belong to an AFP family which is represented in different taxa and can be found in other organisms related to sea ice (Colwellia spp., Navicula glaciei, Chaetoceros neogracile and Stephos longipes and Leucosporidium antarcticum) and Antarctic inland ice bacteria (Flavobacteriaceae), as well as in cold-tolerant fungi (Typhula ishikariensis, Lentinula edodes and Flammulina populicola).
Several structures for sea ice AFPs have been solved. This family of proteins fold into a beta helix that form a flat ice-binding surface. Unlike the other AFPs, there is not a singular sequence motif for the ice-binding site.
AFP found from the metagenome of the ciliate Euplotes focardii and psychrophilic bacteria has an efficient ice re-crystallization inhibition ability. 1 μM of Euplotes focardii consortium ice-binding protein (EfcIBP) is enough for the total inhibition of ice re-crystallization in –7.4 °C temperature. This ice-recrystallization inhibition ability helps bacteria to tolerate ice rather than preventing the formation of ice. EfcIBP produces also thermal hysteresis gap, but this ability is not as efficient as the ice-recrystallization inhibition ability. EfcIBP helps to protect both purified proteins and whole bacterial cells in freezing temperatures. Green fluorescent protein is functional after several cycles of freezing and melting when incubated with EfcIBP. Escherichia coli survives longer periods in 0 °C temperature when the efcIBP gene was inserted to E. coli genome. EfcIBP has a typical AFP structure consisting of multiple beta-sheets and an alpha-helix. Also, all the ice-binding polar residues are at the same site of the protein. | 1 | Biochemistry |
Supercritical drying is a method of removing solvent without surface tension effects. As a liquid dries, the surface tension drags on small structures within a solid, causing distortion and shrinkage. Under supercritical conditions there is no surface tension, and the supercritical fluid can be removed without distortion. Supercritical drying is used in the manufacturing process of aerogels and drying of delicate materials such as archaeological samples and biological samples for electron microscopy. | 7 | Physical Chemistry |
The catalytic cycle begins with coordination of the Cu(I) species to the olefin, followed by oxidative addition at the γ position and an allylic shift to displace the leaving group. This generates a Cu(III) allyl complex intermediate. Finally, reductive elimination yields the final product and regenerates Cu(I). A Cu(III) intermediate has not been confirmed by isolation from allylic substitutions, but Cu(III) intermediates have been isolated before, thus providing credence to the proposed mechanism. If reductive elimination does not occur fast enough, the γ allyl complex can isomerize to the α allyl complex and yield the α substituted isomer as a byproduct. This side pathway can be prevented by using electron withdrawing ligands on copper, typically a cyanide or halide ligand, which promote reductive elimination. | 0 | Organic Chemistry |
In chemistry, intervalence charge transfer, often abbreviated IVCT or even IT, is a type of charge-transfer band that is associated with mixed valence compounds. It is most common for systems with two metal sites differing only in oxidation state. Quite often such electron transfer reverses the oxidation states of the sites. The term is frequently extended to the case of metal-to-metal charge transfer between non-equivalent metal centres. The transition produces a characteristically intense absorption in the electromagnetic spectrum. The band is usually found in the visible or near infrared region of the spectrum and is broad.
The process can be described as follows:
:LM-bridge-ML + hν → LM-bridge-ML
where L is a bridging ligand. | 7 | Physical Chemistry |
Predominant reaction in Mond Gas Process: C + 2HO = CO+ 2H
The Mond gas was composed of roughly:
* 12% CO (Carbon monoxide)
* 28% H (Hydrogen)
* 2.2% CH (Methane)
* 16% CO (Carbon dioxide)
* 42% N (Nitrogen) | 7 | Physical Chemistry |
When two carbonyl groups are coupled and undergo a McMurry reaction, there is a possibility of the formation of cycloalkenes under specific conditions. When both carbonyls are within the same molecule and not sufficiently separated from each other, a cycloalkene can be formed through an intramolecular McMurry reaction. | 0 | Organic Chemistry |
Often, reactive intermediates such as carbocations and free radicals have more delocalized structure than their parent reactants, giving rise to unexpected products. The classical example is allylic rearrangement. When 1 mole of HCl adds to 1 mole of 1,3-butadiene, in addition to the ordinarily expected product 3-chloro-1-butene, we also find 1-chloro-2-butene. Isotope labelling experiments have shown that what happens here is that the additional double bond shifts from 1,2 position to 2,3 position in some of the product. This and other evidence (such as NMR in superacid solutions) shows that the intermediate carbocation must have a highly delocalized structure, different from its mostly classical (delocalization exists but is small) parent molecule. This cation (an allylic cation) can be represented using resonance, as shown above.
This observation of greater delocalization in less stable molecules is quite general. The excited states of conjugated dienes are stabilised more by conjugation than their ground states, causing them to become organic dyes.
A well-studied example of delocalization that does not involve π electrons (hyperconjugation) can be observed in the non-classical 2-Norbornyl cation Another example is methanium (). These can be viewed as containing three-center two-electron bonds and are represented either by contributing structures involving rearrangement of σ electrons or by a special notation, a Y that has the three nuclei at its three points.
Delocalized electrons are important for several reasons; a major one is that an expected chemical reaction may not occur because the electrons delocalize to a more stable configuration, resulting in a reaction that happens at a different location. An example is the Friedel–Crafts alkylation of benzene with 1-chloro-2-methylpropane; the carbocation rearranges to a tert-butyl group stabilized by hyperconjugation, a particular form of delocalization. | 7 | Physical Chemistry |
hnRNPs affect several aspects of the cell cycle by recruiting, splicing, and co-regulating certain cell cycle control proteins. Much of hnRNPs' importance to cell cycle control is evidenced by its role as an oncogene, in which a loss of its functions results in various common cancers. Often, misregulation by hnRNPs is due to splicing errors, but some hnRNPs are also responsible for recruiting and guiding the proteins themselves, rather than just addressing nascent RNAs. | 1 | Biochemistry |
Isocyanates are usually produced from amines by phosgenation, i.e. treating with phosgene:
These reactions proceed via the intermediacy of a carbamoyl chloride (). Owing to the hazardous nature of phosgene, the production of isocyanates requires special precautions. A laboratory-safe variation masks the phosgene as oxalyl chloride.
Another route to isocyanates entails addition of isocyanic acid to alkenes. Complementarily, alkyl isocyanates form by displacement reactions involving alkyl halides and alkali metal cyanates.
Three rearrangement reactions involving nitrenes give isocyanates:
* Schmidt reaction, a reaction where a carboxylic acid is treated with ammonia and hydrazoic acid yielding an isocyanate.
* Curtius rearrangement degradation of an acyl azide to an isocyanate and nitrogen gas.
* Lossen rearrangement, the conversion of a hydroxamic acid to an isocyanate via the formation of an O-acyl, sulfonyl, or phosphoryl intermediate. | 0 | Organic Chemistry |
Mecillinam is used in the treatment of infections due to susceptible gram-negative bacteria, especially urinary tract infections which are most commonly caused by Escherichia coli. Mecillinam is active against most pathogenic Gram-negative bacteria, except Pseudomonas aeruginosa and some species of Proteus. Several studies have also found it to be as effective as other antibiotics for treating Staphylococcus saprophyticus infection, though it is Gram-positive, possibly because mecillinam reaches very high concentrations in urine.
Worldwide resistance to mecillinam in bacteria causing urinary tract infection has remained very low since its introduction; a 2003 study conducted in 16 European countries and Canada found resistance to range from 1.2% (Escherichia coli) to 5.2% (Proteus mirabilis). Another large study conducted in Europe and Brazil obtained similar results — 95.9% of E. coli strains, for instance, were sensitive to mecillinam. | 4 | Stereochemistry |
In molecular physics and chemistry, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and therefore more susceptible to disturbance. The van der Waals force quickly vanishes at longer distances between interacting molecules.
Named after Dutch physicist Johannes Diderik van der Waals, the van der Waals force plays a fundamental role in fields as diverse as supramolecular chemistry, structural biology, polymer science, nanotechnology, surface science, and condensed matter physics. It also underlies many properties of organic compounds and molecular solids, including their solubility in polar and non-polar media.
If no other force is present, the distance between atoms at which the force becomes repulsive rather than attractive as the atoms approach one another is called the van der Waals contact distance; this phenomenon results from the mutual repulsion between the atoms' electron clouds.
The van der Waals forces are usually described as a combination of the London dispersion forces between "instantaneously induced dipoles", Debye forces between permanent dipoles and induced dipoles, and the Keesom force between permanent molecular dipoles whose rotational orientations are dynamically averaged over time. | 6 | Supramolecular Chemistry |
Possible applications for volatiles like volatile organic compounds with VMAA are: maintaining hygiene in hospitals, treating post-harvest contamination, protecting crops against pathogens and pests, and treating infections of the digestive, vaginal or respiratory tract. | 1 | Biochemistry |
Specific areas of the 16S rRNA in the Enterobacteriaceae genus are bound by oligonucleotide probes, which aids in monitoring the quality of drinking water. Specifically, E. coli is labelled with a soybean peroxidase-labeled peptide nucleic acid (PNA) probes that bind to a specific sequence in their 16S rRNA. When used in conjunction with a chemiluminescent substrate, light is produced where each colony of E. coli is located, indicating that they are present in the sample. | 3 | Analytical Chemistry |
This stage is useful for identifying patients with bacterial overgrowth syndrome. The physician will provide a course of 2 weeks of antibiotics to eliminate any possible bacterial overgrowth and repeat the test to check whether radio-labeled Vitamin B12 would be found in urine or not. | 1 | Biochemistry |
Drospirenone is an agonist of the PR, the biological target of progestogens like progesterone. It has about 35% of the affinity of promegestone for the PR and about 19 to 70% of the affinity of progesterone for the PR. Drospirenone has antigonadotropic and functional antiestrogenic effects as a result of PR activation. The ovulation-inhibiting dosage of drospirenone is 2 to 3 mg/day. Inhibition of ovulation occurred in about 90% of women at a dose of 0.5 to 2 mg/day and in 100% of women at a dose of 3 mg/day. The total endometrial transformation dose of drospirenone is about 50 mg per cycle, whereas its daily dose is 2 mg for partial transformation and 4 to 6 mg for full transformation. The medication acts as a contraceptive by activating the PR, which suppresses the secretion of luteinizing hormone, inhibits ovulation, and alters the cervical membrane and endometrium.
Due to its antigonadotropic effects, drospirenone inhibits the secretion of the gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and suppresses gonadal sex hormone production, including of estradiol, progesterone, and testosterone. Drospirenone alone at 4 mg/day has been found to suppress estradiol levels in premenopausal women to about 40 to 80 pg/mL depending on the time of the cycle. No studies of the antigonadotropic effects of drospirenone or its influence on hormone levels appear to have been conducted in men. In male cynomolgus monkeys however, 4 mg/kg/day oral drospirenone strongly suppressed testosterone levels. | 4 | Stereochemistry |
Cobalt is essential to the metabolism of all animals. It is a key constituent of cobalamin, also known as vitamin B, the primary biological reservoir of cobalt as an ultratrace element. Bacteria in the stomachs of ruminant animals convert cobalt salts into vitamin B, a compound which can only be produced by bacteria or archaea. A minimal presence of cobalt in soils therefore markedly improves the health of grazing animals, and an uptake of 0.20 mg/kg a day is recommended because they have no other source of vitamin B.
Proteins based on cobalamin use corrin to hold the cobalt. Coenzyme B features a reactive C-Co bond that participates in the reactions. In humans, B has two types of alkyl ligand: methyl and adenosyl. MeB promotes methyl (−CH) group transfers. The adenosyl version of B catalyzes rearrangements in which a hydrogen atom is directly transferred between two adjacent atoms with concomitant exchange of the second substituent, X, which may be a carbon atom with substituents, an oxygen atom of an alcohol, or an amine. Methylmalonyl coenzyme A mutase (MUT) converts MMl-CoA to Su-CoA, an important step in the extraction of energy from proteins and fats.
Although far less common than other metalloproteins (e.g. those of zinc and iron), other cobaltoproteins are known besides B. These proteins include methionine aminopeptidase 2, an enzyme that occurs in humans and other mammals that does not use the corrin ring of B, but binds cobalt directly. Another non-corrin cobalt enzyme is nitrile hydratase, an enzyme in bacteria that metabolizes nitriles. | 1 | Biochemistry |
Initially, analytes in a metabolomic sample comprise a highly complex mixture. This complex mixture can be simplified prior to detection by separating some analytes from others. Separation achieves various goals: analytes which cannot be resolved by the detector may be separated in this step; in MS analysis, ion suppression is reduced; the retention time of the analyte serves as information regarding its identity. This separation step is not mandatory and is often omitted in NMR and "shotgun" based approaches such as shotgun lipidomics.
Gas chromatography (GC), especially when interfaced with mass spectrometry (GC-MS), is a widely used separation technique for metabolomic analysis. GC offers very high chromatographic resolution, and can be used in conjunction with a flame ionization detector (GC/FID) or a mass spectrometer (GC-MS). The method is especially useful for identification and quantification of small and volatile molecules. However, a practical limitation of GC is the requirement of chemical derivatization for many biomolecules as only volatile chemicals can be analysed without derivatization. In cases where greater resolving power is required, two-dimensional chromatography (GCxGC) can be applied.
High performance liquid chromatography (HPLC) has emerged as the most common separation technique for metabolomic analysis. With the advent of electrospray ionization, HPLC was coupled to MS. In contrast with GC, HPLC has lower chromatographic resolution, but requires no derivatization for polar molecules, and separates molecules in the liquid phase. Additionally HPLC has the advantage that a much wider range of analytes can be measured with a higher sensitivity than GC methods.
Capillary electrophoresis (CE) has a higher theoretical separation efficiency than HPLC (although requiring much more time per separation), and is suitable for use with a wider range of metabolite classes than is GC. As for all electrophoretic techniques, it is most appropriate for charged analytes. | 1 | Biochemistry |
Additional reported applications of genome-wide CRISPR screens include the study of: mitochondrial metabolism, bacterial toxin resistance, genetic drivers of metastasis, cancer drug resistance, West Nile virus-induced cell death, and immune cell gene networks. | 1 | Biochemistry |
Companion planting in gardening and agriculture is the planting of different crops in proximity for any of a number of different reasons, including weed suppression, pest control, pollination, providing habitat for beneficial insects, maximizing use of space, and to otherwise increase crop productivity. Companion planting is a form of polyculture.
Companion planting is used by farmers and gardeners in both industrialized and developing countries for many reasons. Many of the modern principles of companion planting were present many centuries ago in forest gardens in Asia, and thousands of years ago in Mesoamerica. The technique may allow farmers to reduce costly inputs of artificial fertilisers and pesticides. | 1 | Biochemistry |
Retinalophototrophs achieve adequate energy conversion via a proton-motive force. In retinalophototrophs, proton-motive force is generated from rhodopsin-like proteins, primarily bacteriorhodopsin and proteorhodopsin, acting as proton pumps along a cellular membrane.
To capture photons needed for activating a protein pump, retinalophototrophs employ organic pigments known as carotenoids, namely beta-carotenoids. Beta-carotenoids present in retinalophototrophs are unusual candidates for energy conversion, but they possess high Vitamin-A activity necessary for retinaldehyde, or retinal, formation. Retinal, a chromophore molecule configured from Vitamin A, is formed when bonds between carotenoids are disrupted in a process called cleavage. Due to its acute light sensitivity, retinal is ideal for activation of proton-motive force and imparts a unique purple coloration to retinalophototrophs. Once retinal absorbs enough light, it isomerizes, thereby forcing a conformational (i.e., structural) change among the covalent bonds of the rhodopsin-like proteins. Upon activation, these proteins mimic a gateway, allowing passage of ions to create an electrochemical gradient between the interior and exterior of the cellular membrane. Ions diffusing outwards across the gradient through proton pumps are then bound to ATP synthase proteins on the cell’s surface. As they diffuse back into the cell, their protons catalyze the creation of ATP (from ADP and a phosphorus ion), providing energy for retinalophototrophic self-sustenance and proliferation. | 5 | Photochemistry |
When insulator sequences are located in close proximity to the promoter of a gene, it has been suggested that they might serve to stabilize enhancer-promoter interactions. When they are located farther away from the promoter, insulator elements would compete with the enhancer and interfere with activation of transcription. Loop formation is common in eukaryotes to bring distal elements (enhancers, promoters, locus control regions) into closer proximity for interaction during transcription. The mechanism of enhancer-blocking insulators then, if in the correct position, could play a role in regulating transcription activation. | 1 | Biochemistry |
The Freundlich adsorption isotherm is mathematically expressed as
In Freundlichs notation (used for his experiments dealing with the adsorption of organic acids on coal in aqueous solutions), signifies the ratio between the adsorbed mass or adsorbate and the mass of the adsorbent , which in Freundlichs studies was coal. In the figure above, the x-axis represents , which denotes the equilibrium concentration of the adsorbate within the solvent.
Freundlich's numerical analysis of the three organic acids for the parameters and according to equation
were:
Freundlich's experimental data can also be used in a contemporary computer based fit. These values are added to appreciate the numerical work done in 1907.
△ K and △ n values are the error bars of the computer based fit. The K and n values itself are used to calculate the dotted lines in the figure.
Equation can also be written as
Sometimes also this notation for experiments in the gas phase can be found:
: = mass of adsorbate
: = mass of adsorbent
: = equilibrium pressure of the gaseous adsorbate in case of experiments made in the gas phase (gas/solid interaction with gaseous species/adsorbed species)
and are constants for a given adsorbate and adsorbent at a given temperature (from there, the term isotherm needed to avoid significant gas pressure fluctuations due to uncontrolled temperature variations in the case of adsorption experiments of a gas onto a solid phase).
: = distribution coefficient
: = correction factor
At high pressure , hence extent of adsorption becomes independent of pressure.
The Freundlich equation is unique; consequently, if the data fit the equation, it is only likely, but not proved, that the surface is heterogeneous. The heterogeneity of the surface can be confirmed with calorimetry. Homogeneous surfaces (or heterogeneous surfaces that exhibit homogeneous adsorption (single site)) have a constant of adsorption. On the other hand, heterogeneous adsorption (multi-site) have a variable of adsorption depending on the percent of sites occupied. When the adsorbate pressure in the gas phase (or the concentration in solution) is low, high-energy sites will be occupied first. As the pressure in the gas phase (or the concentration in solution) increases, the low-energy sites will then be occupied resulting in a weaker of adsorption. | 3 | Analytical Chemistry |
Sonoporation uses ultrasonic frequencies to deliver DNA into cells. The process of acoustic cavitation is thought to disrupt the cell membrane and allow DNA to move into cells. | 1 | Biochemistry |
An E2 elimination occurs when a proton adjacent to a leaving group is extracted by a base with simultaneous elimination of a leaving group and generation of a double bond.
Similar to the relationship between E1 eliminations and S1 mechanisms, E2 eliminations often occur in competition with S2 reactions. This observation is most often noted when the base is also a nucleophile. In order to minimize this competition, non-nucleophilic bases are commonly used to effect E2 eliminations.
E2 eliminations proceed through initial extraction of a proton by a base or nucleophile leading to Elimination of a leaving group justifying the E designation. Because this mechanism proceeds through the interaction of two species (substrate and base/nucleophile), E2 reactions are recognized as bi-molecular. Thus, the involvement of 2 species in the initial phase of the reaction enhances the mechanistic designation to E2. | 0 | Organic Chemistry |
In ammonia production CO and CO are considered poisons to most commonly used catalysts. Methanation catalysts are added after several hydrogen producing steps to prevent carbon oxide buildup in the ammonia synthesis loop as methane does not have similar adverse effects on ammonia synthesis rates. | 0 | Organic Chemistry |
Abnormal proteolytic activity is associated with many diseases. In pancreatitis, leakage of proteases and their premature activation in the pancreas results in the self-digestion of the pancreas. People with diabetes mellitus may have increased lysosomal activity and the degradation of some proteins can increase significantly. Chronic inflammatory diseases such as rheumatoid arthritis may involve the release of lysosomal enzymes into extracellular space that break down surrounding tissues. Abnormal proteolysis may result in many age-related neurological diseases such as Alzheimer's due to generation and ineffective removal of peptides that aggregate in cells.
Proteases may be regulated by antiproteases or protease inhibitors, and imbalance between proteases and antiproteases can result in diseases, for example, in the destruction of lung tissues in emphysema brought on by smoking tobacco. Smoking is thought to increase the neutrophils and macrophages in the lung which release excessive amount of proteolytic enzymes such as elastase, such that they can no longer be inhibited by serpins such as α-antitrypsin, thereby resulting in the breaking down of connective tissues in the lung. Other proteases and their inhibitors may also be involved in this disease, for example matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs).
Other diseases linked to aberrant proteolysis include muscular dystrophy, degenerative skin disorders, respiratory and gastrointestinal diseases, and malignancy. | 1 | Biochemistry |
Imaging is a useful tool in visualization of the radioligand after injection, with Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT) being the most common types of imaging. PET scans are often utilized after radioligand administration because of the ease of use, image accuracy, and non-invasive nature. While PET and SPECT scans function similarly when imaging radioligands, the main difference lies in the type of radiation used, with PET Scans utilizing positrons and SPECT utilizing gamma rays. When comparing the two modalities, PET offers much better image quality and high diagnostic proficiency, however, the high cost limits the overall availability as well as the short half-lives of the positron-emitting isotopes. Alternatively, SPECT imaging is more dynamic because of the lower cost burden and longer half-lives of single-photon emitters. With advances in technology came hybrid imaging that can combine PET, SPECT, Computed Tomography (CT), and Magnetic Resonance Imaging (MRI). Some hybrid imaging modalities include: SPECT/CT, PET/CT and PET/MRI. Although combined imaging presents both cost and availability barriers, the technology is an extremely useful diagnostic tool. Often, the patient does not have to be moved for both imaging types to be completed and the clinicians are provided with rich, multi-dimensional imaging. | 1 | Biochemistry |
The electrical field of terahertz pulses is measured in a detector simultaneously illuminated with an ultrashort laser pulse. Two common detection schemes are used in THz-TDS: photoconductive sampling and electro-optical sampling. The power of THz pulses can be detected by bolometers (heat detectors cooled to liquid-helium temperatures), but since bolometers can only measure the total energy of a terahertz pulse rather than its electric field over time, they are unsuitable for THz-TDS.
Because the measurement technique is coherent, it naturally rejects incoherent radiation. Additionally, because the time slice of the measurement is extremely narrow, the noise contribution to the measurement is extremely low.
The signal-to-noise ratio (S/N) of the resulting time-domain waveform depends on experimental conditions (e.g., averaging time). However due to the coherent sampling techniques described, high S/N values (>70 dB) are routinely observed with 1 minute averaging times. | 7 | Physical Chemistry |
Victor Meyer suggested a method for determining the types of alcohol i.e. (primary, secondary or tertiary). In this method the sample alcohol is treated with PI to get the iodoalkane which is again treated with AgNO to get the nitroalkane. The nitroalkane is then treated with nitrous acid which is obtained by NaNO and HCl. The resulting solution is treated with KOH and the colour is observed. The red, blue and no colour indicates the primary, secondary and tertiary alcohol respectively. | 7 | Physical Chemistry |
An allele-specific oligonucleotide (ASO) is a short piece of synthetic DNA complementary to the sequence of a variable target DNA. It acts as a probe for the presence of the target in a Southern blot assay or, more commonly, in the simpler dot blot assay. It is a common tool used in genetic testing, forensics, and molecular biology research.
An ASO is typically an oligonucleotide of 15–21 nucleotide bases in length. It is designed (and used) in a way that makes it specific for only one version, or allele, of the DNA being tested. The length of the ASO, which strand it is chosen from, and the conditions by which it is bound to (and washed from) the target DNA all play a role in its specificity. These probes can usually be designed to detect a difference of as little as 1 base in the target's genetic sequence, a basic ability in the assay of single-nucleotide polymorphisms (SNPs), important in genotype analysis and the Human Genome Project. To be detected after it has bound to its target, the ASO must be labeled with a radioactive, enzymatic, or fluorescent tag. The Illumina Methylation Assay technology takes advantage of ASO to detect one base pair difference (cytosine versus thymine) to measure methylation at a specific CpG site. | 1 | Biochemistry |
Sulfur is intimately involved in production of fossil fuels and a majority of metal deposits because of its ability to act as an oxidizing or reducing agent. The vast majority of the major mineral deposits on Earth contain a substantial amount of sulfur including, but not limited to: sedimentary exhalative deposits (SEDEX), Carbonate-hosted lead-zinc ore deposits (Mississippi Valley-Type MVT) and porphyry copper deposits. Iron sulfides, galena and sphalerite will form as by-products of hydrogen sulfide generation, as long as the respective transition or base metals are present or transported to a sulfate reduction site. If the system runs out of reactive hydrocarbons economically viable elemental sulfur deposits may form. Sulfur also acts as a reducing agent in many natural gas reservoirs and generally ore forming fluids have a close relationship with ancient hydrocarbon seeps or vents.
Important sources of sulfur in ore deposits are generally deep-seated, but they can also come from local country rocks, sea water, or marine evaporites. The presence or absence of sulfur is one of the limiting factors on both the concentration of precious metals and its precipitation from solution. pH, temperature and especially redox states determine whether sulfides will precipitate. Most sulfide brines will remain in concentration until they reach reducing conditions, a higher pH or lower temperatures.
Ore fluids are generally linked to metal rich waters that have been heated within a sedimentary basin under the elevated thermal conditions typically in extensional tectonic settings. The redox conditions of the basin lithologies exert an important control on the redox state of the metal-transporting fluids and deposits can form from both oxidizing and reducing fluids. Metal-rich ore fluids tend to be by necessity comparatively sulfide deficient, so a substantial portion of the sulfide must be supplied from another source at the site of mineralization. Bacterial reduction of seawater sulfate or a euxinic (anoxic and HS-containing) water column is a necessary source of that sulfide. When present, the δS values of barite are generally consistent with a seawater sulfate source, suggesting baryte formation by reaction between hydrothermal barium and sulfate in ambient seawater.
Once fossil fuels or precious metals are discovered and either burned or milled, the sulfur become a waste product which must be dealt with properly or it can become a pollutant. There has been a great increase in the amount of sulfur in our present day atmosphere because of the burning of fossil fuels. Sulfur acts as a pollutant and an economic resource at the same time. | 9 | Geochemistry |
In a liquid mixture, the fugacity of each component is equal to that of a vapor component in equilibrium with the liquid. In an ideal solution, the fugacities obey the Lewis-Randall rule:
where is the mole fraction in the liquid and is the fugacity of the pure liquid phase. This is a good approximation when the component molecules have similar size, shape and polarity.
In a dilute solution with two components, the component with the larger molar fraction (the solvent) may still obey Raoults law even if the other component (the solute) has different properties. That is because its molecules experience essentially the same environment that they do in the absence of the solute. By contrast, each solute molecule is surrounded by solvent molecules, so it obeys a different law known as Henrys law. By Henrys law, the fugacity of the solute is proportional to its concentration. The constant of proportionality (a measured Henrys constant) depends on whether the concentration is represented by the mole fraction, molality or molarity. | 7 | Physical Chemistry |
As the name contains the prefix thio-, these compounds contain sulfur. Examples include sinigrin, found in black mustard, and sinalbin, found in white mustard. | 0 | Organic Chemistry |
This is accomplished by comparing the different HERV from different evolutionary periods. For example, this study was done for different hominoids, which ranged from humans to apes and to monkeys. This is difficult to do with PERV because of the large diversity present. | 1 | Biochemistry |
Although organomagnesium compounds are widespread in the form of Grignard reagents, the other organo-group 2 compound are almost exclusively of academic interest. Organoberyllium chemistry is limited due to the cost and toxicity of beryllium. Calcium is nontoxic and cheap but organocalcium compounds are difficult to prepare, strontium and barium compounds even more so. One use for these type of compounds is in chemical vapor deposition. | 0 | Organic Chemistry |
Anthocyanins may be used as pH indicators because their color changes with pH; they are red or pink in acidic solutions (pH < 7), purple in neutral solutions (pH ≈ 7), greenish-yellow in alkaline solutions (pH > 7), and colorless in very alkaline solutions, where the pigment is completely reduced. | 3 | Analytical Chemistry |
In nuclear physics, spectral bands refer to the electromagnetic emission of polyatomic systems, including condensed materials, large molecules, etc. Each spectral line corresponds to the difference in two energy levels of an atom. In molecules these levels can split. When the number of atoms is large, one gets a continuum of energy levels, the so-called "spectral bands". They are often labeled in the same way as the monatomic lines.
The bands may overlap. In general, the energy spectrum can be given by a density function, describing the number of energy levels of the quantum system for a given interval. Spectral bands have constant density, and when the bands overlap, the corresponding densities are added.
Band spectra is the name given to a group of lines that are closely spaced and arranged in a regular sequence that appears to be a band. It is a colored band, separated by dark spaces on the two sides and arranged in a regular sequence. In one band, there are various sharp and wider color lines, that are closer on one side and wider on other. The intensity in each band falls off from definite limits and indistinct on the other side. In complete band spectra, there is a number lines in a band.
This spectra is produced when the emitting substance is in the molecular state. Therefore, they are also called molecular spectra.
It is emitted by a molecule in vacuum tube, C-arc core with metallic salt. The band spectrum is the combination of many different spectral lines, resulting from molecular vibrational, rotational, and electronic transition.
Spectroscopy studies spectral bands for astronomy and other purposes.
Many systems are characterized by the spectral band to which they respond. For example:
* Musical instruments produce different ranges of notes within the hearing range.
* The electromagnetic spectrum can be divided into many different ranges such as visible light, infrared or ultraviolet radiation, radio waves, X-rays and so on, and each of these ranges can in turn be divided into smaller ranges.
* A radio communications signal must occupy a range of frequencies carrying most of its energy, called its bandwidth. A frequency band may represent one communication channel or be subdivided into many. Allocation of radio frequency ranges to different uses is a major function of radio spectrum allocation. | 7 | Physical Chemistry |
Since the ERK signaling pathway is involved in both physiological and pathological cell proliferation, it is natural that ERK1/2 inhibitors would represent a desirable class of antineoplastic agents. Indeed, many of the proto-oncogenic "driver" mutations are tied to ERK1/2 signaling, such as constitutively active (mutant) receptor tyrosine kinases, Ras or Raf proteins. Although no MKK1/2 or ERK1/2 inhibitors were developed for clinical use, kinase inhibitors that also inhibit Raf kinases (e.g. Sorafenib) are successful antineoplastic agents against various types of cancer. MEK inhibitor cobimetinib has been investigated in pre-clinical lung cancer models in combination with inhibition of the PI3K pathway, where the two drugs lead to a synergistic response.
JNK kinases are implicated in the development of insulin resistance in obese individuals as well as neurotransmitter excitotoxicity after ischaemic conditions. Inhibition of JNK1 ameliorates insulin resistance in certain animal models. Mice that were genetically engineered to lack a functional JNK3 gene - the major isoform in brain – display enhanced ischemic tolerance and stroke recovery. Although small-molecule JNK inhibitors are under development, none of them proved to be effective in human tests yet. A peptide-based JNK inhibitor (AM-111, a retro-inverse D-motif peptide from JIP1, formerly known as XG-102) is also under clinical development for sensorineural hearing loss.
p38 was once believed to be a perfect target for anti-inflammatory drugs. Yet the failure of more than a dozen chemically different compounds in the clinical phase suggests that p38 kinases might be poor therapeutic targets in autoimmune diseases. Many of these compounds were found to be hepatotoxic to various degree and tolerance to the anti-inflammatory effect developed within weeks. An alternative approach is to evaluate the potential for targeting upstream MAPKs, such as ASK1. Studies in animal models of inflammatory arthritis have yielded promising results, and ASK1 has recently been found to be unique amongst the MAPKs in that it is inducible by inflammatory cytokines such as TNF-α. | 1 | Biochemistry |
UV-induced RNA-antibody crosslinking was added on top of m6A-seq to produce PA-m6A-seq (photo-crosslinking-assisted m6A-seq) which increases resolution up to ~23nt. First, 4-thiourodine (4SU) is incorporated into the RNA by adding 4SU in growth media, some incorporation sites presumably near m6A location. Immunoprecipitation is then performed on full-length RNA using m6A-specific antibody [36]. UV light at 365 nm is then shined onto RNA to activate the crosslinking to the antibody with 4SU. Crosslinked RNA was isolated via competition elution and fragmented further to ~25-30nt; proteinase K was used to dissociate the covalent bond between crosslinking site and antibody. Peptide fragments that remain after antibody removal from RNA cause the base to be read as a C as opposed to a T during reverse transcription, effectively inducing a point mutation at the 4SU crosslinking site. The short fragments are subjected to library construction and Illumina sequencing, followed by finding the consensus methylation sequence.
The presence of the T to C mutation helps increase the signal to noise ratio of methylation site detection as well as providing greater resolution to the methylation sequence.
One shortcoming of this method is that m6A sites that did not incorporate 4SU can't be detected.
Another caveat is that position of 4SU incorporation can vary relative to any single m6A residue, so it still remains challenging to precisely locate m6A site using the T to C mutation. | 1 | Biochemistry |
Since DNA replication needs a supply of guanine nucleotides, there must be some co-ordination between the DNA replication machinery and the gua operon. One method through which this happens is the DnaA protein. DnaA is a protein which recognises the origin of replication, promotes a local unwinding of an AT rich DNA region and finally guides the helicase DnaB to its entry site. DnaA is the replication initiation factor which causes DNA replication if present in sufficient concentration.
When replication happens, the origin of replication creates a "sink" for DnaA proteins. So genes which are negatively modulated by DnaA, like those of the gua operon are derepressed. Two potential DnaA binding sites, one on the gua promoter and another 200 bp downstream of the IMP dehydrogenase initiation codon on the guaB gene exist. It is thought that both the former and the latter sequences play a part, the latter part being vital and DNA binding at these sequences negatively affect transcription of the gene.
While growing on media in which growth rates are low, cAMP binds to a cAMP receptor protein forming a complex which has regulatory properties. This complex binds to a region 100 bp upstream of the guaB transcription start site which then represses the gua operon. It is a matter of debate of how this complex interacts with RNA polymerase from as long as around 100 bit/s away. One view suggests the involvement of an unknown regulatory factor. In any case, the complex confers growth rate dependent control to the promoter region of the operon.
The repressor purR encoded by purR genes controls the synthesis of enzymes involved in purine biosynthesis. A putative 16 bp pur operator was found in the gua promoter. The purR repressor works with other co-repressors, for example guanine which is a co-repressor in E. coli.
The gua mRNA leader has the potential for forming a stable stem-loop secondary structure incorporating the first 37 nucleotides of the transcript. As the ribosome binding site is sequestered in the stem loop, this structure may be involved in translational regulation.
The gua promoter lies back-to-back with the xseA promoter (encoding the mismatch repair enzyme exonuclease VII). Such close spacing of promoters may have regulatory significance and will lead to steric hindrance as the RNA polymerase molecules try to bind simultaneously. Inactivation of one promoter will naturally lead to greater expression of the other promoter. Other mechanisms include FIS (factor for inversion stimulation) which sterically hinders RNA polymerase binding. But the role of FIS is not yet properly investigated. | 1 | Biochemistry |
Kuftin was invited to Central Asia to carry out explorations in 1949. He first reconnoitered Turkmenistan and selected a very large tepe (hill), the Altyndepe (in Turkmen language meaning: the "Golden Hill" ). This tepe overlooks the Tedzen delta at the foot of Kopetdag. He found a Neolithic settlement extending into Bronze Age in southern Turkmenistan near the village of Miana, a settlement of 25 ha area with a total stratification thickness of with an strip of human habitation. This excavated tepe turned out to be a large settlement, in length and in width, and was identified as a major Bronze Age town. From the highest point of this tepe, a trench was dug to a depth of and the section was logged, which revealed layers of the Bronze Age, of neolithic and Eneolithic periods. Ceramics collected from the different layers of the trench enabled Kuftin to establish the sequence and chronology of the findings. One year after he started sequencing the site, he died suddenly and was replaced by Vadim Mikhailovich Masson who published a book on the Bronze Age sequence of this site. The settlement of Ilgynly had also shifted to Altyndepe. Early Bronze period fort walls with decorated towers and a huge entrance had encircled this settlement, though when found, they were in ruins. Discoveries by Soviet archeologists dated the finds at this place, in a chronological order, to the later half of the third millennium BC. Altyn-Depe also provided a link to the several Bronze Age cultures of Eurasia.
The most notable findings in the burial ground of the elite, located in the outskirts of Altyndepe, were "a disk-like stone weight, a miniature column, more than 1500 beads, a steatite plate with an image of cross and half-moon, a moulded clay wolf, as well as a golden head of a bull with a turquoise sickle inlaid in the forehead".
Excavations revealed bone and copper artifacts of the fifth millennium BC (Neolithic period), female figurines painted with ornaments, and necklaces of the fourth million BC.
Brick walls of thickness with brick kilns and a hearth in the middle of the house dated to early third millennium, and small temple buildings and rectangular hearths of Namazga V type of the middle third millennium were also found.
In the period from late third millennium to early second millennium, the antiquaries revealed an urban habitation with artisans' houses. Also unearthed were 62 double-tiered kilns, beads and seals.
Four stepped ziggurats were found. Further were revealed female terracotta figurines with plaited hair, stone vessels, hafted bronze and copper daggers with flat blades, tabbed silver and bronze seals.
The further findings were,
* Paintings of animals such as goats, eagles, and panthers.
* Three headed composite animal.
* A priest's tomb with gold heads of a wolf and a bull.
* Other tombs with silver ornaments, precious stones and seals.
*One quarter of a ‘nobility’ seal with two signs in Indus script conjectured to be that of Bronze Age settlers in Altyndepe.
However, the settlement gradually disappeared (it was deserted around 1600 BC) as a result of climatic changes; people migrated to the Mugrab region, another area of South Uzbekistan (Sapali), and Northern Afghanistan (Dashli). Further, these findings confirmed the Middle Asian interaction from the north to the Oxus civilization. | 8 | Metallurgy |
* Trypanosoma: UUA, UUG, CUG ;
* Leishmania: AUU, AUA ;
* Tetrahymena: AUU, AUA, AUG ;
* Paramecium: AUU, AUA, AUG, AUC, GUG, GUA(?).
(Pritchard et al., 1990) | 1 | Biochemistry |
Deuterium (hydrogen-2, symbol H or D, also known as heavy hydrogen) is one of two stable isotopes of hydrogen (the other is protium, or hydrogen-1). The deuterium nucleus, called a deuteron, contains one proton and one neutron, whereas the far more common protium has no neutrons in the nucleus. Deuterium has a natural abundance in Earth's oceans of about one atom of deuterium among every 6,420 atoms of hydrogen (see heavy water). Thus deuterium accounts for about 0.0156% by number (0.0312% by mass) of all hydrogen in the oceans: tonnes of deuterium – mainly in form of HOD (or HOH or HHO) and only rarely in form of DO (or HO) – in tonnes of water. The abundance of deuterium changes slightly from one kind of natural water to another (see Vienna Standard Mean Ocean Water).
The name deuterium comes from Greek , meaning "second". Deuterium was discovered by American chemist Harold Urey in 1931. Urey and others produced samples of heavy water in which the deuterium content had been highly concentrated. The discovery of deuterium won Urey a Nobel Prize in 1934.
Deuterium is destroyed in the interiors of stars faster than it is produced. Other natural processes are thought to produce only an insignificant amount of deuterium. Nearly all deuterium found in nature was produced in the Big Bang 13.8 billion years ago, as the basic or primordial ratio of H to H (about 26 atoms of deuterium per million hydrogen atoms) has its origin from that time. This is the ratio found in the gas giant planets, such as Jupiter. The analysis of deuterium–protium ratios in comets found results very similar to the mean ratio in Earths oceans (156 atoms of deuterium per million hydrogen atoms). This reinforces theories that much of Earths ocean water is of cometary origin. The deuterium–protium ratio of the comet 67P/Churyumov–Gerasimenko, as measured by the Rosetta space probe, is about three times that of Earth water. This figure is the highest yet measured in a comet. Deuterium–protium ratios thus continue to be an active topic of research in both astronomy and climatology. | 9 | Geochemistry |
Multiple bismuth-containing clusters were reported, some of them synthesized through carbon monoxide ligand loss from the previously reported bismuth complexes. Strained cluster complexes with monodentate as well as bridging carbon monoxide units have also been isolated, such as [{Cp(μ-CO)Fe}(μ-Bi)] and [(µ-Bi)Co(CO)(µ-CO)].
Spiro-like clusters such as [{Ru(CO)}(µ-Bi){(µ-H)Ru(CO)} and cubane-like ones as [BiCo*] are representatives as well. The former displays a tetracoordinate bismuth metallic center along with a dicoordinated hydride ligand. The structure of the latter is cubic with the edges alternating bismuth and cobalt metallic centers. | 0 | Organic Chemistry |
The first stage is called roughing, which produces a rougher concentrate. The objective is to remove the maximum amount of the valuable mineral at as coarse a particle size as practical. Grinding costs energy. The goal is to release enough gangue from the valuable mineral to get a high recovery. Some concentrators use a preflotation step to remove low density impurities such as carbonaceous dust. The rougher concentrate is normally subjected to further stages of flotation to reject more of the undesirable minerals that also reported to the froth, in a process known as cleaning. The resulting material is often subject to further grinding (usually called regrinding). Regrinding is often undertaken in specialized regrind mills, such as the IsaMill. The rougher flotation step is often followed by a scavenger flotation step that is applied to the rougher tailings to further recover any of the target minerals. | 8 | Metallurgy |
In molecular cloning, a vector is any particle (e.g., plasmids, cosmids, Lambda phages) used as a vehicle to artificially carry a foreign nucleic sequence – usually DNA – into another cell, where it can be replicated and/or expressed. A vector containing foreign DNA is termed recombinant DNA. The four major types of vectors are plasmids, viral vectors, cosmids, and artificial chromosomes. Of these, the most commonly used vectors are plasmids. Common to all engineered vectors are an origin of replication, a multicloning site, and a selectable marker.
The vector itself generally carries a DNA sequence that consists of an insert (in this case the transgene) and a larger sequence that serves as the "backbone" of the vector. The purpose of a vector which transfers genetic information to another cell is typically to isolate, multiply, or express the insert in the target cell. All vectors may be used for cloning and are therefore cloning vectors, but there are also vectors designed specially for cloning, while others may be designed specifically for other purposes, such as transcription and protein expression. Vectors designed specifically for the expression of the transgene in the target cell are called expression vectors, and generally have a promoter sequence that drives expression of the transgene. Simpler vectors called transcription vectors are only capable of being transcribed but not translated: they can be replicated in a target cell but not expressed, unlike expression vectors. Transcription vectors are used to amplify their insert.
The manipulation of DNA is normally conducted on E. coli vectors, which contain elements necessary for their maintenance in E. coli. However, vectors may also have elements that allow them to be maintained in another organism such as yeast, plant or mammalian cells, and these vectors are called shuttle vectors. Such vectors have bacterial or viral elements which may be transferred to the non-bacterial host organism, however other vectors termed intragenic vectors have also been developed to avoid the transfer of any genetic material from an alien species.
Insertion of a vector into the target cell is usually called transformation for bacterial cells, transfection for eukaryotic cells, although insertion of a viral vector is often called transduction. | 1 | Biochemistry |
The EXPOSE-E experiments are:
* PROCESS, study photochemical organic compounds in Earth orbit. Relevant to comets, meteorites, Mars and Titan.
* ADAPT, study molecular adaptation strategies of microorganisms in analogues to meteoritic matter to different space and planetary UV climate conditions.
* PROTECT, study of spores' resistance to space conditions, and their ability to recover from the damages done by such an exposition. For planetary protection purposes.
* LiFE (Lichens and Fungi Experiment), study of radiations effect on lichens, fungi and symbiotes in space conditions.
* SEEDS, test plant seed as a terrestrial model for a panspermia vehicle and as a source of universal UV screens and study of their ability to resist radiations.
* Dosis, Dobis & R3D, passive dosimeters for ionizing radiation measurement and the R3D (Radiation Risk Radiometer-Dosimeter E) active radiation measuring instrument. | 1 | Biochemistry |
Terminal restriction fragment length polymorphism (TRFLP or sometimes T-RFLP) is a molecular biology technique for profiling of microbial communities based on the position of a restriction site closest to a labelled end of an amplified gene. The method is based on digesting a mixture of PCR amplified variants of a single gene using one or more restriction enzymes and detecting the size of each of the individual resulting terminal fragments using a DNA sequencer. The result is a graph image where the x-axis represents the sizes of the fragment and the y-axis represents their fluorescence intensity. | 1 | Biochemistry |
One major use of CFCs has been as propellants of aerosols, including metered-dose inhalers for drugs used to treat asthma. The conversion of these devices and treatments from CFC to propellants that do not deplete the ozone layer is almost complete. Production and import is now banned in the United States. | 2 | Environmental Chemistry |
The anthocyanins, anthocyanidins with sugar group(s), are mostly 3-glucosides of the anthocyanidins. The anthocyanins are subdivided into the sugar-free anthocyanidin aglycones and the anthocyanin glycosides. As of 2003, more than 400 anthocyanins had been reported, while later literature in early 2006, puts the number at more than 550 different anthocyanins. The difference in chemical structure that occurs in response to changes in pH, is the reason why anthocyanins often are used as pH indicators, as they change from red in acids to blue in bases through a process called halochromism. | 3 | Analytical Chemistry |
The equation of "organic" with living organisms comes from the now-abandoned idea of vitalism that attributed a special force to life that alone could create organic substances. This idea was first questioned after the artificial synthesis of urea by Friedrich Wöhler in 1828. | 0 | Organic Chemistry |
Concrete, in perfumery, is a waxy mass obtained by solvent extraction of fresh plant material. It is usually used for the production of absolutes. | 7 | Physical Chemistry |
[RhH(CO)(PPh)] was first prepared by the reduction of [RhCl(CO)(PPh)], e.g. with sodium tetrahydroborate, or triethylamine and hydrogen, in ethanol in the presence of excess triphenylphosphine:
:[RhCl(CO)(PPh)] + NaBH + PPh → [RhH(CO)(PPh)] + NaCl + BH
It can also be prepared from an aldehyde, rhodium trichloride and triphenylphosphine in basic alcoholic media. | 0 | Organic Chemistry |
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