cadherins

Cadherins are developmentally regulated, calcium-dependent homophilic cell-cell adhesion molecules (CAMs), through which cell-cell and cell-matrix interactions are mediated.[]im[]

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cAMP-dependent protein kinase

cAMP-dependent protein kinase (PKA) is a serine/threonine kinase with catalytic (protein phosphorylating) activity that is modulated by cAMP levels.

Specific protein kinases transfer a phosphate group from a donor such as ATP to amino acid acceptors in proteins, while protein phosphatases remove the phosphate groups that have been attached by protein kinases.

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capping

Capping occurs shortly after initiation of transcription, and is a stage of RNA processing in which the 5’ end of the nascent pre-mRNA is capped with a 7-methyl guanosine nucleotide, 7-methylguanylate.

The 5' cap is retained in mature mRNAs. Capping is required to protect the RNA transcript from degradation. It plays an important role in mRNA transport to the cytoplasm and in the initiation of protein synthesis (translation).

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catabolite gene activator protein

A catabolite gene activator protein (im), also called catabolite gene activator, is a cAMP dependent RNA polymerase that up-regulates gene expression by binding the polymerase at or near the DNA to be transcribed (families).

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cell adhesion

Cell adhesion relies upon specialized transmembrane cellular adhesion molecules (CAMs) that usually extend from the intracellular space to the extracellular space where they may bind to other cell membranes or to the extracellular matrix.

CAMs include cadherins, focal adhesion kinase (FAK), members of the Ig superfamily, integrins, and selectins. Some signaling molecules act as adhesion receptors, and cluster in focal adhesions upon ligand binding. (Rho protein, Rho GTPase).

 Cell Adhesion Molecules  Second Messengers  Cell signaling

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cellular stress response

The cellular stress response (heat-shock response) protects organisms from damage resulting from environmental stressors such as heat, UV light, trace metals, and xenobiotics.

Physical or chemical stress inactivates or down-regulates many genes, including many housekeeping genes, while up-regulating stress genes that perform orchestrated induction of key proteins necessary for cellular protein repair and degradation systems. Stress genes are highly conserved in biological evolution and play similar roles in organisms from bacteria to humans.

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chromatin

Chromatin is the composite form of DNA in nuclear eukaryotic chromosomes in which long helical strands of DNA are wrapped around structural proteins called histones (diagram).

Chromatin occurs in two forms euchromatin and heterochromatin.

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chromosome

A chromosome contains a long strand of deoxyribonucleic acid containing genes, regulatory sequences, and non-coding sequences of nucleotides, condensed around histone proteins as chromatin.[]im[]

The full chromosomal complement of a cell comprises the genome, which is the complete hereditary information of an organism contained within macromolecules of archival DNA.

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cis-acting elements

Cis-acting elements are DNA sequences in the vicinity of the structural portion of a gene, which are required for gene expression.

Most often, signal elements act only on the intramolecular nucleotide sequence to which they are attached, and they are said to act "in cis".

 Regulatory Proteins Sequences

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codon

Triplets of DNA nucleotides arranged in sequence along DNA are transcribed into the codons of mRNA strands.[]im[]code[]

Each tri-nucleotide sequence in the DNA reading frame and its transcribed mRNA codon signals for the insertion of one amino acid into a polymerizing peptide chain. The sequence of codons in genes determines the sequence of amino acids inserted into peptide, polypeptide and protein chains (primary structure).

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cognate

The adjective 'cognate' signifies specificity of binding, as applied, for example, to antigen-antibody or protein-ligand or enzyme-substrate pairs.

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commensal

Commensal organisms (symbionts) benefit from living symbiotically within another organism while not harming the host organism.

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constitutive

In biology, constitutive refers to any molecule that is constantly produced or to any gene that is constantly expressed (without need for regulatory stimulation by regulatory proteins or transcription factors).

Also referred to as 'wild-type', such genes are to be contrasted with inducible genes, which are subject to up-and down-regulation. Molecules such as proteins and RNAs that are not constitutive have cellular levels that are regulated by protein degradation or RNA decay.

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CpG island

CpG islands are discrete clusters of nonmethylated CpG dinucleotide segments composed of large numbers of phosphodiester-linked cytosine "p" guanine nucleobases. CpG islands comprise about 1 to 2% of the mammalian genome (4, 7), and are located near or within approximately 40% of promoters in mammalian genes.

The formal definition of a CpG island is 'a region with at least 200 bp and with a GC percentage that is greater than 50% and with an observed/expected CpG ratio that is greater than 0.6.'

In a CpG island, a cytosine nucleotide occurs phosphodiester-bonded to a guanine nucleotide. The "p" in the CpG notation distinguishes a cytosine adjacent to a phosphodiester-linked guanine from a cytosine base paired to a guanine on a complementary strand.

Unlike CpG sites in the coding region of a gene, bases within CpG islands are unmethylated if the promoted genes are expressed. Most CpG islands are associated with genes or recognition sites for restriction enzmes. This includes all genes that are ubiquitously expressed (housekeeping genes) plus many genes with a tissue-restricted pattern of expression. Many human and mouse major histocompatibility locus (MHC) genes contain CpG-rich regions (64), yet only the β-chain genes for class II MHC have CpG-rich regions [r].

Promoters are normally located at the upstream edge of the CpG island, such that one or more of the 5′ exons of the gene generally fall within the island region. Although most CpG islands are nonmethylated in all tissues, a small proportion of islands become methylated during development [s]. 82% of all Not 1 sites are found in CpG islands.


Toll-like receptors, a type of innate immune system pattern-recognition receptor, recognize and ligate unmethylated CpGs as a subclass of pathogen-associated molecular pattern (PAMP)

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cyclin-dependent kinases

Cyclin-dependent kinases (CDKs) are a subclass of serine/threonine protein kinases that play a role in regulation of transcription and mRNA processing, and in regulation of the cell cycle. Specific protein kinases transfer a phosphate group from a donor such as ATP to amino acid acceptors in proteins, while protein phosphatases remove the phosphate groups that have been attached by protein kinases.

The activity of cyclin-dependent kinases is modulated by binding to cyclins, which are proteins so-named because their levels vary periodically during the cell cycle. The binding of cyclins to cyclin-dependent kinases regulates CDK activity, selecting the proteins to be phosphorylated. Although levels of CDK-molecules are constant during the cell cycle, their activities vary because of the regulatory function of the cyclins. Thus, periodic protein degradation is an important general control mechanism of the cell cycle.

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cytolysis

Cytolysis (cell lysis) results when the plasma membrane is ruptured, resulting in osmosis-induced swelling and ultimately cell death.

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cytokines

Cytokines are small proteins that regulate and mediate immunity, inflammation, and hemotopoiesis.

Cytokines are secreted de novo in response to immune stimuli, and usually act briefly, locally, at very low concentrations (the exception being endocrine action at distant cells). Cytokines bind to specific membrane receptors, which then signal the cell via second messengers, often tyrosine kinases, to alter cellular activity (gene expression).

Table  Immune Cytokines.

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