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Home >> Dictionary of Bioinformatics, Biochemistry, Biotechnology >> Cosmid - CpG Methylation
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Corynebacteria
A genus of small Gram-positive rod shaped bacteria with aerobic to chemorganic metabolism. One of the members of this group of bacteria is C.diphtheriae, which causes diphtheria.
COS cells
A derivative of CV-1 monkey cells infected with SV40 virus. They do not produce SV40 virus but express the SV40 early genes, the T antigens required for viral replication. COS cells are useful as hosts in cloning experiments.
Cos ends
The 12-base, single stranded, complementary sticky ends of bacteriophage lambda (l) DNA. Also termed cos sites.
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Cosmid
A plasmid vector that contains cos sites of phage lambda (l) and one or more selectable markers such as an antibiotic resistance gene. Cosmids combine the best features of plasmids and phages. They can be packaged into phage heads and can undergo replication in plasmid form. Cosmids have higher cloning capacity than plasmids and phages and enable large, 40-50 kb DNA fragments to be cloned with high efficiency.
Cot
The product of DNA concentration and time of reaction in a reassociation reaction.
Cot curve
The graph that shows the proportion of renatured DNA against cot. When double stranded DNA is heated, it denatures to form single strands. On cooling, the complementary strands of DNA tend to anneal or renature. The extent of renaturation depends on the product of DNA concentration in moles of nucleotides per litre, and time in seconds. The cot at which half the DNA has renatured is the half-cot, which is an index of the degree of complexity of the DNA.
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Cotransduction
The introduction of two linked genes into a bacterial cell on the same fragment of DNA by transformation.
Contransfection
The simultaneous transfection of two markers. For example, the simultaneous introduction of baculovirus and transfer vector into insect cells in culture.
Cotransformation
A technique in which host cells are incubated with two types of plasmid, one of which is selectable, whereas the other is nonselectable. Cells that have been transformed with the first plasmid are selected. Transformation with the second (nonselectable) plasmid is possible if the transformation is carried out at high DNA concentration. This method is often used in experiments with mammalian cells.
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Cotranslational transfer
The insertion of one end of a polypeptide into the membrane of the endoplasmic reticulum before the synthesis of the polypeptide is completed.
Cotransport
Transport of an ion or a small molecule against a concentration gradient coupled to the movement of a second molecule down its concentration gradient in the same (symport) or opposite (antiport) direction.
Cotyledon
A seed leaf that develops as part of the plant embryo and provides nutrients to the germinating seeding.
Coulter counter
An instrument that counts cells by measuring changes in resistance that take place when cells in suspension pass through a small slit.
Coumarins
Vitamin K antagonists (eg. Warfarin) that cause a decrease in plasma levels of prothrombin and the factors VII, IX and X. These agents inhibit vitamin L-dependent g-carboxylation of glutamater residues in these clotting factors. Coumarins prevent clot formation on prosthetic implants and can be used for longer periods than heparin. However, excess warmfarin can cause haemorrhage, which can be reversed by administration of vitamin K.
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Countercurrent distribution
A chromatographic separation process based on the distribution of a compound between two immiscible liquid phase. These phases may be mixtures of solvents, buffers, salts and various Complexing agents with neither phase supported by adsorbent nor paper.
Countercurrents exchange
A process by which water without solute is reabsorbed from the DCT and the collecting duct along the osmotic gradient created by counter current multiplication. By this mechanism, the urine becomes concentrated.
Countercurrent immunoelectrophoresis
An immunotechnique technique that involves simultaneous electrophoresis of the antigen and antibody in a gel in opposite directions resulting in precipitation at a point between them.
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This method produces visible precipitation lines within 30 minutes and is more sensitive that strandard double diffusion techniques. It is used to detect antigens such as a-fetoprotein in serum.
Cotranslational
Refers to the import of a protein into the endoplasmic reticulum before the polypeptide chain is fully synthesized.
Cos sites
See cos ends.
Cosegregation
Inheritance of two genetic conditions together.
Countercurrent multiplication
An active process whereby high medullary osmolality created in the renal medulla reduces the osmolality of urine producing a dilute urine. As the tubular filtrate passes down the descending limb, it becomes hyperosmotic. As a result, water without solute is lost in the decending limb.
Counts per minute/per second (c.p.m./c.p.s.)
The recorded rate of radioactive decay.
Coupled reaction
Two chemical reactions that share a common intermediate. The intermediate functions as a means of energy transfer from one reaction to another.
Coupled transport
Obligatory simultaneous transport of two solutes across the membrane.
Coupling
1. A measure of interconnections among modules in a programme structure. 2. The phase state in which either two dominant or two recessive alleles of two different genes occur on the same chromosome. Also called cis configuration.
Covalent Bond
A chemical bond formed by sharing electron pairs.
Covalent chromatography
A technique developed to separate thiol-containing proteins by using their interaction with an immobilized ligand containing a disulphide group.
Covalent Closed Circle (CCC)
A DNA duplex with no free ends. The two strands are interlinked and remain together even after denaturation. In its native form, a CCC adopts a Supercoiled configuration.
Covariance
Coincident change at two or more positions in related sequences that may influence the secondary structures of RNA or protein molecules.
Coxsackie virus
An antigenically distinct enterovirus found in the intestines and excreted in the faeces.
cPCR
See competitive PCR.
cpDNA
The DNA of plant plastids, including chloroplasts.
CpG island
A DNA sequence rich in CG dinucleotides usually found at the 5’ end of eukaryotic genes.
CpG methylation
In mammals, transcriptionally inactive regions of the chromatin that can be recognised by methylation of cytosine residues in the sequence 5’-CG-3’. CpG methylation signals the degree of chromosomal packaging at the sites of expressed genes. Islands of unmethylated CpG are found near the 5’ end of the eukaryotic genes. The CpG islands are 1-2 kb in length and present throughout the genome.
There are 45,000 CpG islands in the human genome of which 50 percent are associated with housekeeping genes and the rest with cell-type specific genes. The structure of chromatin in CpG islands shows changes associated with gene expression including decreased content of histone H1, extensive Acetylation of histones and DNase I hypersensitivity.
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