2.6.6: Key Terms

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apoptosis: programmed cell death

autocrine signal: signal that is sent and received by the same or similar nearby cells

autoinducer: signaling molecule secreted by bacteria to communicate with other bacteria of its kind

cell-surface receptor: cell-surface protein that transmits a signal from the exterior of the cell to the interior, even though the ligand does not enter the cell

chemical synapse: small space between axon terminals and dendrites of nerve cells where neurotransmitters function

cyclic AMP (cAMP): second messenger that is derived from ATP

cyclic AMP-dependent kinase: (also, protein kinase A, or PKA) kinase that is activated by binding to cAMP

diacylglycerol (DAG): cleavage product of PIP₂ that is used for signaling within the plasma membrane

dimer: chemical compound formed when two molecules join together

dimerization: (of receptor proteins) interaction of two receptor proteins to form a functional complex called a dimer

endocrine cell: cell that releases ligands involved in endocrine signaling (hormones)

endocrine signal: long-distance signal that is delivered by ligands (hormones) traveling through an organism's circulatory system from the signaling cell to the target cell

enzyme-linked receptor: cell-surface receptor with intracellular domains that are associated with membrane-bound enzymes

extracellular domain: region of a cell-surface receptor that is located on the cell surface

G-protein-linked receptor: cell-surface receptor that activates membrane-bound G-proteins to transmit a signal from the receptor to nearby membrane components

growth factor: ligand that binds to cell-surface receptors and stimulates cell growth

inhibitor: molecule that binds to a protein (usually an enzyme) and keeps it from functioning

inositol phospholipid: lipid present at small concentrations in the plasma membrane that is converted into a second messenger; it has inositol (a carbohydrate) as its hydrophilic head group

inositol triphosphate (IP₃): cleavage product of PIP₂ that is used for signaling within the cell

intercellular signaling: communication between a cell

internal receptor: (also, intracellular receptor) receptor protein that is located in the cytosol of a cell and binds to ligands that pass through the plasma membrane

intracellular mediator: (also, second messenger) small molecule that transmits signals within a cell

intracellular signaling: communication within cells

ion channel-linked receptor: cell-surface receptor that forms a plasma membrane channel, which opens when a ligand binds to the extracellular domain (ligand-gated channels)

kinase: enzyme that catalyzes the transfer of a phosphate group from ATP to another molecule

ligand: molecule produced by a signaling cell that binds with a specific receptor, delivering a signal in the process

mating factor: signaling molecule secreted by yeast cells to communicate to nearby yeast cells that they are available to mate

neurotransmitter: chemical ligand that carries a signal from one nerve cell to the next

paracrine signal: signal between nearby cells that is delivered by ligands traveling in the liquid medium in the space between the cells

phosphatase: enzyme that removes the phosphate group from a molecule that has been previously phosphorylated

phosphodiesterase: enzyme that degrades cAMP, producing AMP, to terminate signaling

quorum sensing: method of cellular communication used by bacteria that informs them of the abundance of similar (or different) bacteria in the environment

receptor: protein in or on a target cell that bind to ligands

second messenger: small, non-protein molecule that propagates a signal within the cell after activation of a receptor causes its release

signal integration: interaction of signals from two or more different cell-surface receptors that merge to activate the same response in the cell

signal transduction: propagation of the signal through the cytoplasm (and sometimes also the nucleus) of the cell

signaling cell: cell that releases signal molecules that allow communication with another cell

signaling pathway: (also signaling cascade) chain of events that occurs in the cytoplasm of the cell to propagate the signal from the plasma membrane to produce a response

synaptic signal: chemical signal (neurotransmitter) that travels between nerve cells

target cell: cell that has a receptor for a signal or ligand from a signaling cell