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 the figure below. Which of the following would enhance this effect of the acetylcholine? plasma membrane closed K' channel GTP Pr complex activated α subunit K CHANNEL open K'channel OPENING EXTRACELLULAR SPACE CYTOSOL GTP G-PROTEIN INACTIVATION K" CHANNEL CLOSING closed K' channel rt inactive G protein GOP addition of a drug that prevents the subunit from exchanging GDP for GTP O mutations in the acetylcholine receptor that weaken the interaction between the receptor and acetylcholine O addition of a high concentration of a nonhydrolyzable analog of GTP O mutations in the acetylcholine receptor that weaken the interaction between the receptor and the G protein Acetylcholine acts at a GPCR on heart muscle to make the heart beat more slowly. It does so by ultimately opening K channels in the plasma membrane (as diagrammed in the figure below), which decreases the cell's excitability by making it harder to depolarize the plasma membrane. Indicate whether the following condition would increase or decrease the effect of acetylcholine. Addition of a drug that stimulates the GTPase activity of the Ga subunit will plasma membrane closed K' channel GTP activated By complex activated α subunit K CHANNEL open K' channel OPENING EXTRACELLULAR SPACE CYTOSOL GTP G-PROTEIN NACTIVATION K CHANNEL CLOSING closed K·channel nactive G protein GDP increase the effect O decrease the effect Acetylcholine acts at a GPCR on heart muscle to make the heart beat more slowly. It does so by ultimately opening K channels in the plasma membrane (as diagrammed in the figure below), which decreases the cell's excitability by making it harder to depolarize the plasma membrane. Indicate whether the following condition would increase or decrease the effect of acetylcholine. Mutations in the K+ channel that keep it closed all the time will. plasma membrane closed K channel GTP activated Py complex activated α subunit K"CHANNEL OPENING open K+ channel K' EXTRACELLULAR SPACE CYTOSOL GTP G-PROTEIN NACTIVATION Cdosed K' c CLOSING (C nactive G protein GDP O decrease the effect increase the effect Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen, as depicted in the figure below Which of the following statements is FALSE? adrenaline activated e subunit of stimulatory G protein (G CYTOSOL activated GPCR (adrenergic receptor activated adenylyl cyclase inactive PKA CAMP active PKA active kinase inactive active glycogen kinase inactive GLYCOGEN A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glucose available A constitutively active mutant form of PKA in skeletal muscle cells would not increase the affinity of adrenaline for the adrenaline receptor A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available A constitutively active mutant form of PKA in skeletal muscle cells would lead to a decrease in the amount of unphosphorylated phosphorylase kinase

Answer 1

Question 01:-

(C) addition of high concentration of non-hydrolyzable analog of GTP -All the other choices will make it more difficult for the signal to proceed from the GPCR to the K+ channel.

Question02:-

(B) Decrease the etfect- An increase in the GTPase activity of the Gα subunit will decrease the length of time that the G protein is active.

Question 03:-

(A) Decrease the effect- If the K+ channel remains closed, acetylcholine will not slow the heart.

Question 04:-

(C) A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available.

A constitutively active mutant form of PKA in skeletal muscle cells would lead to a decrease in the amount of glycogen available, because active PKA stimulates enzymes that are responsible for the breakdown of glycogen so that glucose can be produced. (All
the other statements are true.)