Question

Which of the following is an example of negative feedback in the glucagon signaling pathway:

PKA activates cyclic nucleotide phosphodiesterase, which converts cAMP to AMP

PKA inhibits cyclic nucleotide phosphodiesterase, which converts cAMP to AMP

PKA activates adenylate cyclase GAP, which inactivates adenylate cyclase PKA inhibits adenylate cyclase GAP, which inactivates adenylate cyclase

PKA activates phosphorylase kinase phosphatase, which dephosphorylates phosphorylase kinase

PKA inhibits phosphorylase kinase phosphatase, which dephosphorylates phosphorylase kinase ?

Answer 1

Glucagon binds with G protein coupled receptor on the cell surface. The G protein in turn activates adenylate cyclase enzyme which converts ATP to cAMP. The cAMP stimulates the enzyme protein kinase A which in turn stimulates phosphorylase kinase which then phosphorylates glycogen phosphorylase b converting it into phosphorylase a which then releases glucose-1-phosphate from glycogen polymers.

When there is enough glucose, the protein kinase A (PKA) activates cyclic nucleotide phosphodiesterase which decreases the concentration of cAMP by converting them into AMP. This breaks the activation cascade resulting in the decrease of blood glucose levels. So, the answer for this question is option 1.