G-Protien Coupled Receptors(GPCR) Flashcards
describe the basic structure of a G-protein
peripheral membrane protein, consists of 3 polypeptide subunits, contains guanine nucleotide binding site on alpha subunit , can exist as multiple types
describe the structure of the G-protein coupled receptor
integral membrane protein, single polypeptide with extracellular NH2 and COOH termini
describe how GCPRs are activated
activated by agonist binding to the GCPR to which they preferentially couple
describe the difference between the active and inactive states of the GCPR
when inactive GDP is bound to the guanine nucleotide binding site of the alpha subunit, whereas when in an active state GTP is bound instead, as well as the alpha and beta, gamma subunits dissociate
describe what happens when the GPCR is activated
when activated by binding of agonist there is a conformation change which is transmitted to the G-protein alpha subunit
describe the effects of the G-protein alpha subunit after the GCPR is activated
releases GDP and allows GTP to bind in its place, separates from the receptor and the beta-gamma dimer(subunit dissociation), generates a free GTP-bound alpha-subunit and beta-gamma dimer which both act as signalling units
describe how GPCRs work when there is no signalling
receptor is unoccupied, GDP is bound to the alpha-subunit, the effector is not modulated
describe how the GPCRs work when they are turned on by a signal
agonist activates receptor, G-protein couples with receptor, GDP dissociates and GTP binds to the alpha-subunit, G-protein alpha-subunit dissociates and combines with and modifies activity of effector
describe how the GCPRs work to turn off
the alpha-subunit acts as an enzyme to convert GTP to GDP and P, the signal is turned off and the G-protein alpha-subunit recombines with the beta-gamma dimer
