NIME Next Batch PGI Quest in Delhi from 10 August to 20 August
A. G protein acts as inhibitory and excitatory as cc-subunit exists in two forms
B. GTP binds to G protein in resting state
C. All the three subunits a, p. andy should bind to other for G protein to act
D. G protein binds to hormone on cell surface
TRUE about G protein receptors is
A. G protein acts as inhibitory and excitatory as cc-subunit exists in two forms B. GTP binds to G protein in resting state
C. All the three subunits a, p. andy should bind to other for G protein to act
D. G protein binds to hormone on cell surface
Ans. A. (G protein acts as inhibitory and excitatory as cc-subunit exists in
two forms)
Explanation
Adenyl cyclase system—Aseries of events occur at the membrane level that influence the activity of adenylate cyclase leading to the synthesis of cAMP. The process is mediated by G protein. The mechanism of cAMP synthesis is briefly described as
Adenyl cyclase system—Aseries of events occur at the membrane level that influence the activity of adenylate cyclase leading to the synthesis of cAMP. The process is mediated by G protein. The mechanism of cAMP synthesis is briefly described as
follows:
• The hormones bind to a stimulatory receptor at the membrane, which in turn stimulates the G-protein.
• The hormones bind to a stimulatory receptor at the membrane, which in turn stimulates the G-protein.
• G-protein
is a trimmer consisting of cc, 3, and y subunits. The cc-subunit is bound to
GDP in the native G protein structure.
• The hormone—receptor complex causes exchange of GDP with GTP on a subunit and dissociates it from G 3, y. The resultant subunit bound to GTP stimulates, and hence is called as adenylate cyclase.
• The hormone—receptor complex causes exchange of GDP with GTP on a subunit and dissociates it from G 3, y. The resultant subunit bound to GTP stimulates, and hence is called as adenylate cyclase.
•
ATP is converted to cAMP by activated adenylate cyclase.
•
The GDP bound to as is hydrolyzed to GDP and this as GDP combines with G 3, y
to regenerate the original G cc, 3, y proteins.
•
Some hormones inhibit the adenylate cyclase activity. This effect is mediated
through inhibitory G proteins. The structure of (f3 and y sub-units of GI is
similar to that of G protein with stimulatory effect. However, a subunit (Gcc)
differs in structure with a molecular weight of 41,000.
