General principles of cellular communication

# Glossary

consensus sequence
  A consensus sequence is a common order of nucleotides in DNA, or amino acids in proteins. Proteins interact with DNA, and with other proteins, via specified consensus sequences. In DNA, the consensus sequence is a generalised nucleotide sequence derived from comparisons of closely related DNA sequences from many places within, or between, genomes.

covalent modification
  The covalent linking to protein amino acid side-chains of groups that can affect their function and/or the localisation of the protein in the cell; such modifications include methylation, acetylation, glycosylation, phosphorylation and lipidation.

domains
  Physically and functionally distinct regions within a protein molecule.

G-protein-coupled receptors (GPCRs)
  A family of integral membrane proteins that activate signal transduction processes inside cells; they typically bind extrinsic signals via their carboxy-terminal extracellular domains, and via a conformational change alter the activity of associated GTP-binding proteins. They are sometimes referred to as 7-helix transmembrane (7TM) receptors, serpentine receptors or heptahelical receptors because they possess seven transmembrane domains. GPCRs can also be considered as guanine nucleotide-exchange factors since they promote the exchange of GTP for GDP on associated G-proteins.

GTPase-activating proteins (GAPs)
  GTPase-activating proteins associate with GTP-binding proteins and accelerate the rate of GTP hydrolysis.

guanine nucleotide-binding proteins (G-proteins)
  Also known as GTP-binding proteins. Proteins that act as molecular switches, being activated when GTP is exchanged for GDP. Can be monomeric proteins, or exist as a trimeric complex of α, β and γ subunits. With trimeric G-proteins, the α subunit binds guanine nucleotides.

guanine nucleotide-exchange factor (GEF)
  Proteins that associate with GTP-binding proteins and accelerate the exchange of GTP for GDP to switch on signalling.

ligand
  A molecule or ion that binds to a receptor or other protein at a specific binding site and may cause activation or inhibition of the receptor and its downstream signalling processes.

mitogen-activated protein kinase (MAP kinase or MAPK)
  Kinases that were so-named because they were first identified in the signalling pathways activated by molecules that stimulate cells to divide (i.e. mitogens). MAP kinases are components of intracellular signalling cascades that are activated by extrinsic ligands binding to cell membrane receptors; often function in a cascade of kinases in which the final kinase phosphorylates target proteins including transcription factors.

mitogen-activated protein kinase (MAP kinase) pathway
  Signalling pathways involving MAP kinases.

molecular switches
  Cellular proteins that change between an active (on) and an inactive (off) conformation. The conformational change is usually brought about by the addition/removal of a phosphate group, either by phosphorylation/dephosphorylation of an amino acid residue or by GTP/GDP exchange.

motifs
  Sequences of amino acids that are found in a number of related proteins. Alternatively, sequences of bases that are found in functionally related gene segments in different genes, e.g. the target sites for transcription factors. This term is also used to describe combinations of secondary structure (supersecondary structures) in proteins.

phosphorylation
  The transfer of a phosphate group from one molecule to another. Many proteins are phosphorylated by kinases that transfer the terminal phosphate group from ATP. Phosphorylation changes the conformation of a target protein so that its activity, or ability to interact with other molecules, is altered.

pleiotropic
  Describes a cellular process, signal or gene that has more than one effect, or more than one phenotypic outcome. At the genetic level, describes a situation where a single mutation affects two or more apparently unrelated phenotypic traits.

OpenLearn - General principles of cellular communication
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