|
LuxS
The enzyme S-ribosylhomocysteine lyase (EC 4.4.1.21) catalyzes the reaction :''S''-(5-deoxy-D-ribos-5-yl)-L-homocysteine = L-homocysteine + (4''S'')-4,5-dihydroxypentan-2,3-dione Nomenclature This enzyme belongs to the family of lyases, specifically the class of carbon-sulfur lyases. The systematic name of this enzyme class is ''S''-(5-deoxy-D-ribos-5-yl)-L-homocysteine L-homocysteine-lyase 4''S'')-4,5-dihydroxypentan-2,3-dione-forming''. Other names in common use include ''S''-ribosylhomocysteinase, and LuxS. This enzyme participates in methionine metabolism. Structure and function LuxS is a homodimeric iron-dependent metalloenzyme containing two identical tetrahedral metal-binding sites similar to those found in peptidases and amidases. Furthermore, LuxS is involved in the synthesis of autoinducer AI-2 ( autoinducer-2), which mediates quorum sensing in roughly half of bacterial species. AI-2, a furanosyl borate diester, is a small signaling molecule generated by bacter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Quorum Sensing
In biology, quorum sensing or quorum signaling (QS) is the process of cell-to-cell communication that allows bacteria to detect and respond to cell population density by gene regulation, typically as a means of acclimating to environmental disadvantages. Quorum sensing is a type of cellular signaling, and can be more specifically considered a type of paracrine signaling. However, it also contains traits of autocrine signaling: a cell produces both an autoinducer molecule and the receptor for the autoinducer. As one example, quorum sensing enables bacteria to restrict the expression of specific genes to the high cell densities at which the resulting phenotypes will be most beneficial, especially for phenotypes that would be ineffective at low cell densities and therefore too energetically costly to express. Many species of bacteria use quorum sensing to coordinate gene expression according to the density of their local population. In a similar fashion, some social insects use q ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Catalysis
Catalysis () is the increase in rate of a chemical reaction due to an added substance known as a catalyst (). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quickly, very small amounts of catalyst often suffice; mixing, surface area, and temperature are important factors in reaction rate. Catalysts generally react with one or more reactants to form intermediates that subsequently give the final reaction product, in the process of regenerating the catalyst. The rate increase occurs because the catalyst allows the reaction to occur by an alternative mechanism which may be much faster than the noncatalyzed mechanism. However the noncatalyzed mechanism does remain possible, so that the total rate (catalyzed plus noncatalyzed) can only increase in the presence of the catalyst and never decrease. Catalysis may be classified as either homogeneous, whose components are dispersed in the same phase (usual ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Autoinducer-2
Autoinducer-2 (AI-2) is a furanosyl borate diester or tetrahydroxy furan (species dependent) that—as the name suggests—is an autoinducer, a member of a family of signaling molecules used in quorum sensing. AI-2 is one of only a few known biomolecules incorporating boron. First identified in the marine bacterium '' Vibrio harveyi'', AI-2 is produced and recognized by many Gram-negative and Gram-positive bacteria. AI-2 arises by the reaction of 4,5-dihydroxy-2,3-pentanedione, which is produced enzymatically, with boric acid and is recognized by the two-component sensor kinase LuxPQ in Vibrionaceae. AI-2 is actively transported by the Lsr ABC-type transporter into the cell in Enterobacteriaceae and few other bacterial taxa such as ''Pasteurella'', ''Photorhabdus'', ''Haemophilus'', and ''Bacillus'', where it is phosphorylated by LsrK. Then, Phospho-AI-2 binds the transcriptional repressor protein, LsrR, which subsequently is released from the promoter/operator region of the ls ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Population Density
Population density (in agriculture: Standing stock (other), standing stock or plant density) is a measurement of population per unit land area. It is mostly applied to humans, but sometimes to other living organisms too. It is a key geographical term.Matt RosenberPopulation Density Geography.about.com. March 2, 2011. Retrieved on December 10, 2011. Biological population densities Population density is population divided by total land area, sometimes including seas and oceans, as appropriate. Low densities may cause an extinction vortex and further reduce fertility. This is called the Allee effect after the scientist who identified it. Examples of the causes of reduced fertility in low population densities are: * Increased problems with locating sexual mates * Increased inbreeding Human densities Population density is the number of people per unit of area, usually transcribed as "per square kilometre" or square mile, and which may include or exclude, for example, ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bacteria
Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit the air, soil, water, Hot spring, acidic hot springs, radioactive waste, and the deep biosphere of Earth's crust. Bacteria play a vital role in many stages of the nutrient cycle by recycling nutrients and the nitrogen fixation, fixation of nitrogen from the Earth's atmosphere, atmosphere. The nutrient cycle includes the decomposition of cadaver, dead bodies; bacteria are responsible for the putrefaction stage in this process. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, suc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gene
In biology, the word gene has two meanings. The Mendelian gene is a basic unit of heredity. The molecular gene is a sequence of nucleotides in DNA that is transcribed to produce a functional RNA. There are two types of molecular genes: protein-coding genes and non-coding genes. During gene expression (the synthesis of Gene product, RNA or protein from a gene), DNA is first transcription (biology), copied into RNA. RNA can be non-coding RNA, directly functional or be the intermediate protein biosynthesis, template for the synthesis of a protein. The transmission of genes to an organism's offspring, is the basis of the inheritance of phenotypic traits from one generation to the next. These genes make up different DNA sequences, together called a genotype, that is specific to every given individual, within the gene pool of the population (biology), population of a given species. The genotype, along with environmental and developmental factors, ultimately determines the phenotype ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cell Signalling
In biology, cell signaling (cell signalling in British English) is the process by which a cell interacts with itself, other cells, and the environment. Cell signaling is a fundamental property of all cellular life in both prokaryotes and eukaryotes. Typically, the signaling process involves three components: the signal, the receptor, and the effector. In biology, signals are mostly chemical in nature, but can also be physical cues such as pressure, voltage, temperature, or light. Chemical signals are molecules with the ability to bind and activate a specific receptor. These molecules, also referred to as ligands, are chemically diverse, including ions (e.g. Na+, K+, Ca2+, etc.), lipids (e.g. steroid, prostaglandin), peptides (e.g. insulin, ACTH), carbohydrates, glycosylated proteins (proteoglycans), nucleic acids, etc. Peptide and lipid ligands are particularly important, as most hormones belong to these classes of chemicals. Peptides are usually polar, hydrophilic molecules ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homocysteine
Homocysteine (; symbol Hcy) is a non-proteinogenic α-amino acid. It is a homologous series, homologue of the amino acid cysteine, differing by an additional methylene bridge (). It is biosynthesized from methionine by the removal of its terminal Cε methyl group. In the body, homocysteine can be recycled into methionine or converted into cysteine with the aid of Vitamin B6, vitamin B6, Folate, B9, and Vitamin B12, B12. High levels of homocysteine in the blood (hyperhomocysteinemia) is regarded as a marker of cardiovascular disease, likely working through atherogenesis, which can result in Ischemia, ischemic injury. Therefore, hyperhomocysteinemia is a possible risk factor for coronary artery disease. Coronary artery disease occurs when an atherosclerotic plaque blocks blood flow to the Coronary artery, coronary arteries, which supply the heart with oxygenated blood. Hyperhomocysteinemia has been correlated with the occurrence of blood clots, heart attacks, and strokes, although ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cell Signalling
In biology, cell signaling (cell signalling in British English) is the process by which a cell interacts with itself, other cells, and the environment. Cell signaling is a fundamental property of all cellular life in both prokaryotes and eukaryotes. Typically, the signaling process involves three components: the signal, the receptor, and the effector. In biology, signals are mostly chemical in nature, but can also be physical cues such as pressure, voltage, temperature, or light. Chemical signals are molecules with the ability to bind and activate a specific receptor. These molecules, also referred to as ligands, are chemically diverse, including ions (e.g. Na+, K+, Ca2+, etc.), lipids (e.g. steroid, prostaglandin), peptides (e.g. insulin, ACTH), carbohydrates, glycosylated proteins (proteoglycans), nucleic acids, etc. Peptide and lipid ligands are particularly important, as most hormones belong to these classes of chemicals. Peptides are usually polar, hydrophilic molecules ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Autoinducer
In biology, an autoinducer is a signaling molecule that enables detection and response to changes in the population density of bacterial cells. Synthesized when a bacterium reproduces, autoinducers pass outside the bacterium and into the surrounding medium. They are a key component of the phenomenon of quorum sensing: as the density of quorum-sensing bacterial cells increases, so does the concentration of the autoinducer. A bacterium’s detection of an autoinducer above some minimum threshold triggers altered gene expression. Performed by both Gram-negative and Gram-positive bacteria, detection of autoinducers allows them to sense one another and to regulate a wide variety of physiological activities, including symbiosis, virulence, motility, production of antibiotics, and formation of biofilms. Autoinducers take a number of different forms depending on the species of bacteria, but their effect is in many cases similar. They allow bacteria to communicate both within and between ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lyase
In biochemistry, a lyase is an enzyme that catalyzes the breaking (an elimination reaction) of various chemical bonds by means other than hydrolysis (a substitution reaction) and oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ..., often forming a new double bond or a new ring structure. The reverse reaction is also possible (called a Michael reaction). For example, an enzyme that catalyzed this reaction would be a lyase: : ATP → cAMP + PPi Lyases differ from other enzymes in that they require only one substrate for the reaction in one direction, but two substrates for the reverse reaction. Nomenclature Systematic names are formed as "''substrate group-lyase''." Common names include decarboxylase, dehydratase, aldolase, etc. When the product is more importan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Biosynthesis
Biosynthesis, i.e., chemical synthesis occurring in biological contexts, is a term most often referring to multi-step, enzyme-Catalysis, catalyzed processes where chemical substances absorbed as nutrients (or previously converted through biosynthesis) serve as enzyme substrate (chemistry), substrates, with conversion by the living organism either into simpler or more complex Product (chemistry), products. Examples of biosynthetic pathways include those for the production of amino acids, lipid membrane components, and nucleotides, but also for the production of all classes of biological macromolecules, and of acetyl-coenzyme A, adenosine triphosphate, nicotinamide adenine dinucleotide and other key intermediate and transactional molecules needed for metabolism. Thus, in biosynthesis, any of an array of Chemical compound, compounds, from simple to complex, are converted into other compounds, and so it includes both the catabolism and anabolism (building up and breaking down) of comple ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
