If it were injected directly into liver cells, cAMP would have the effect of: A.

Question

If it were injected directly into liver cells, cAMP would have the effect of: A. Activating G-alpha’s GTPase activity B. Directly catalytic the hydrolysis of GTP on G-alpha C. Activating Protein Kinase A and, therefore, glycogen breakdown D. None of the above; nothing would happen in the absence of the “first messenger” If it were injected directly into liver cells, cAMP would have the effect of: A. Activating G-alpha’s GTPase activity B. Directly catalytic the hydrolysis of GTP on G-alpha C. Activating Protein Kinase A and, therefore, glycogen breakdown D. None of the above; nothing would happen in the absence of the “first messenger” A. Activating G-alpha’s GTPase activity B. Directly catalytic the hydrolysis of GTP on G-alpha C. Activating Protein Kinase A and, therefore, glycogen breakdown D. None of the above; nothing would happen in the absence of the “first messenger”

Explanation / Answer

Option C is the correct answer. cAMP is a second messenger which is synthesized from ATP by adenylate cyclase. Adenylate cyclase is activated by a range of signaling molecules through the activation of adenylate cyclase stimulatory G (Gs)-protein-coupled receptors. Adenylate cyclase in liver cells strongly respond to glucagon. Thus glucagon increases the intracellular level of cAMP. cAMP phosphorylates protein kinase A (PKA) which affect protein phosphatases and ultimately increases the breakdown of glycogen.

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