signal transduction pathway

signal transduction pathways

methods for cells to respond to changing conditions using extracellular and intracellular signals

step 1

release of primary messenger to communicate environmental change

step 2

binding of primary messenger to receptor on cell membrane; changing receptor’s shape to change its function, starts intracellular cascade

step 3

delivery of message via secondary messenger inside cell, amplifies signal

step 4

activation of effectors that alter physiological function to respond (activate or inhibit enzyme, pump, transcription factor)

step 5

termination of signal (either the enzyme is deactivated or the primary messenger dissociates from the receptor)

epinephrine

primary messenger, neurotransmitter in fight or flight response (step 1)

B-androgenic G-protein

receptor for epinephrine, off: alpha bound to GDP, receptor, beta and gamma subunits; on: subunits dissociate, alpha binds GTP instead of GDP; can rebind more inactive alpha to amplify signal (step 2)

adenylate cyclase

binds GTP-alpha subunit, releases cAMP from ATP (step 3)

protein kinase A

activated by cAMP to induce physiological change; not amplifying (step 4)

termination of epinephrine pathway

dissociation of ligand or a-subunit intrinsic GTPase activity → deactivates adenylate cyclase, rebinds alpha subunit to B-androgenic receptor