Acetylcholine binds to a GPCR on heart muscle, making the heart beat more slowly
ID: 79604 • Letter: A
Question
Acetylcholine binds to a GPCR on heart muscle, making the heart beat more slowly. The activated receptor stimulates a G protein, which opens a K+ channel in the plasma membrane, as shown in Figure 1. Which of the following would enhance this effect of the acetylcholine? (a) addition of a high concentration of a non-hydrolyzable analog of GTP (b) addition of a drug that prevents the subunit from exchanging GDP for GTP (c) mutations in the acetylcholine receptor that weaken the interaction between the receptor and acetylcholine (d) mutations in the acetylcholine receptor that weaken the interaction between the receptor and the G protein
acetylcholine At complex plasma membrane EXTRACELLULAR SPACE CYTOSOL GTP GDP G protei activated CHANNEL OPENING INACTIVATIO closed K channel K channe osed K chaExplanation / Answer
Since closing of the K+ ion channel is mainly due by exchanging GTP to GDP. Only after this step G protein attached with the GTP molecule and that cause closing of the K+ ion channel.
Thus, if we prevent the conversion of GDP from GTP, it is possible that G protein will not attach with the GDP molecule and thus we can prevent the closing of K+ ion channel.
So, by adding of a drug that prevents the alpha subunit from exchanging GDP for GTP, we can enhance the effect of acetylcholine.