signal transduction
conversion of an impulse or stimulus from one physical or chemical form to another
cell signaling
the molecular mechanisms by which cells detect and respond to external stimuli and send messages to other cells
hormones
a chemical substance produced by one set of cells in a multicellular organism and transported via body fluids to target tissues on which it exerts a specific effect
local mediators
secreted signal molecule that acts at a short range on adjacent cells
neurotransmitter
small signaling molecule secreted by a nerve cell at a chemical synapse to signal to the postsynaptic cell
receptor proteins
protein that detects a stimulus, usually a change in concentration of a specific molecule, and then initiates a response in the cell
receptor
a cell or cellular component that detects an external signal and triggers a specific cellular response
steroid hormones
lipohilic molecule related to cholesterol that acts as a hormone
nitric oxide
small highly diffusible molecule widely used as an intracellular signal
intracellular signaling molecule
molecule that is part of the mechanism for transducing and transmitting signals inside a cell
intracellular signaling pathway
the set of proteins and small-molecule second messengers that interact with each other to relay a signal from the cell membrane to its final destination in the cytoplasm or nucleus
molecular switch
protein or protein complex that operates in an intracellular signaling pathway and can reversibly switch between an active and inactive state
protein kinase
one of a very large number of enzymes that transfers the terminal phosphate group of ATP to a specific amino acid side chain on a target protein
protein phosphatase
enzyme that removes by hydrolysis a phosphate group from a protein, often with high specificity for the phosphorylated site
serine/threonine kinase
enzyme that phosphorylates specific proteins on serines or threonines
tyrosine kinase
enzyme that phosphorylates specific proteins on tyrosines
GTP binding protein
an allosteric protein whose conformation and activity are determined by its association with either GTP or GDP
ion-channel-coupled receptor
transmembrane receptor protein or protein complex that forms a gated ion channel that opens in response to the binding of a ligand to the external face of the channel
G-protein-coupled receptor
cell-surface receptor that associates with an intracellular trimeric GTP-binding protein after receptor activation by an extracellular ligand.
g protein
one of a large family of GTP-binding proteins composed of three different subunits that are important intermediaries in intracellular signaling pathways
small messenger/second messenger
small molecule formed in or release into the cytosol in response to an extracellular signal that helps to relay the signal to the interior of the cell
adenylyl cyclase
enzyme that catalyzes the formation of cyclic AMP from ATP.
cyclic AMP (cAMP)
nucleotide generated from ATP in response to hormonal stimulation of cell-surface receptors; acts as a signaling molecule by activating protein kinase A; can be hydrolyzed to AMP by phosphodiesterase
cyclic AMP dependent kinase (PKA)
enzyme that phosphorylates target proteins in response to a rise in the intracellular cyclic AMP concentration
phospholipase C
enzyme associated with the plasma membrane that performs a crucial step in inositol phospholipid signaling pathway
inositol phospholipids
(phosphoinositide) minor lipid components of plasma membranes that contain phosphorylated inositol derivatives; important both for distinguishing different intracellular membranes and for signal transduction in eucaryotic cells
diacylglycerol (DAG)
lipid produced by the vlevage of membrane inositol phospholipids in response to extracellular signals; composed of two fatty acid chains linked to glycerol, it serves as a membrane-located signaling molecule to help activate protein kinase C
inositol 1, 4, 5-triphosphate (IP3)
small intracellular signaling molecule produced during activation of the inositol phospholipid signaling pathway; causes CA2+ release from the ER
protein kinase C (PKC)
enzyme that phosphorylates target proteins in response to a rise in diacyglycerol and Ca2+ ions
calmodulin (CaM)
small Ca2+ binding protein that modifies the activity of many target enzyms and membrane transport proteins in response to changes in Ca2+ concentration
Ca2+/calmodulin-dependent protein kinase (CaM kinase)
enzyme that phosphorylates target proteins in response to an increase in Ca2+ ion concentration, through its interaction with the Ca2+ binding protein calmodulin
receptor tyrosine kinase (RTK)
enzyme-coupled receptor in which the intracellular domain has a tyrosine kinase activity which is activated by ligand binding to the receptor's extracellular domain
enzyme-coupled receptor
transmembrane receptor proteins that activate an intracellular enzyme in response to ligand binding to the extracellular part of the receptor
adaption
adjustment of sensitivity of a cell or organism following repeated stimulation
Ras
one of a large family of small GTP-binding proteins that help relay signals from cell-surface of receptors to the nucleus
monomeric gTPase
small, single-subunity GTP-binding protein
MAP kinase
mitogen-activated protein kinase; performs a crucial step in relaying signals from cell-surface receptors to the nucleus
phosphoionositide 3-kinase (PI 3-kinase)
enzyme that phosphorylates inositol phospholipids in the plasma membrane in response to signals received by a cell; the lipids become docking sites for intracellular signaling proteins
cytokine
small protein made and secreted by cells that acts on neighboring cells to alter their behavior; act via cell-surface cytokine receptors
Notch and cytokine receptors
activate a direct pathway to the nucleus; they turn on transcription regulators at the plasma membrane, which then migrate to the nucleus where they activate specific genes
endocrine signals
hormones are carried in the blood to distant target cells
neuronal signals
transmitted along axons to remote target cells
paracrine signals
signals released by cells into extracellular fluid and act locally
contact-dependent
communication through cell to cell contact
autocrine signaling
Cancer cells can also promote their own survival through this type of paracrine signaling
Large and/or hydrophilic molecules
must rely on membrane receptors to relay their message across the membrane
Small and/or hydrophobic molecules
diffuse across the plasma membrane, and bind to intracellular enzymes or intracellular receptor proteins
functions of the intracellular signaling pathways
1) relay the signal onward
2) amplify the signal received (make is stronger so that only a few intracellular signaling molecules can evoke a large intracellular response)
3) receive signals from multiple intracellular signaling pathways and integrate them
Mitogens
are extracellular signal molecules that stimulate cell proliferationq
Akt
stimulates cells to grow in size by activating Tor
Tor
(itself a serine/threonine kinase), stimulates protein synthesis and inhibits protein degradation