Which of the following is an example of negative feedback in the glucagon signal

Question

Which of the following is an example of negative feedback in the glucagon signaling pathway, depicted below? (select two answers)

1.PKA activates cyclic nucleotide phosphodiesterase, which converts cAMP to AMP

2.PKA inhibits cyclic nucleotide phosphodiesterase, which converts cAMP to AMP

3.PKA activates adenylate cyclase GAP, which inactivates adenylate cyclase

4.PKA inhibits adenylate cyclase GAP, which inactivates adenylate cyclase

5.PKA activates phosphorylase kinase phosphatase, which dephosphorylates phosphorylase kinase

6.PKA inhibits phosphorylase kinase phosphatase, which dephosphorylates phosphorylase kinase

Glucagon receptor Adenylate cyclase GAP Adenylate cyclase Glycogen synthase PKA > Glycogen synthesis Cyclic nucleotide phosphodiesterase Phosphorylase Glycoge Glycogenolysis kinase phosphorylase (Glycogen breakdown) Phosphorylase kinase phosphatase AMP

Explanation / Answer

Glucose is stored in the liver in the form of the polysaccharide glycogen, which is a glucan (a polymer made up of glucose molecules). Liver cells (hepatocytes) have glucagon receptors. When glucagon binds to the glucagon receptors, the liver cells convert the glycogen into individual glucose molecules and release them into the bloodstream, in a process known as glycogenolysis. As these stores become depleted, glucagon then encourages the liver and kidney to synthesize additional glucose by gluconeogenesis. Glucagon turns off glycolysis in the liver, causing glycolytic intermediates to be shuttled to gluconeogenesis.

Glucagon binds to the glucagon receptor, a G protein-coupled receptor, located in the plasma membrane. The conformation change in the receptor activates G proteins, a heterotrimeric protein with ?, ?, and ? subunits. When the G protein interacts with the receptor, it undergoes a conformational change that results in the replacement of the GDP molecule that was bound to the ? subunit with a GTP molecule. This substitution results in the releasing of the ? subunit from the ? and ? subunits. The alpha subunit specifically activates the next enzyme in the cascade, adenylate cyclase.

Adenylate cyclase manufactures cyclic adenosine monophosphate (cyclic AMP or cAMP), which activates protein kinase A(cAMP-dependent protein kinase). This enzyme, in turn, activates phosphorylase kinase, which then phosphorylates glycogen phosphorylase b (PYG b), converting it into the active form called phosphorylase a (PYG a). Phosphorylase a is the enzyme responsible for the release of glucose-1-phosphate from glycogen polymers.

Answers:

1. cAMP activates protein kinase A, which further gives glycogenolysis. But if it is used in converting cAMP to AMP then further actual work will not happen. So it will give positive feedback to glucagon signaling pathway to produce more cAMP.

2. negative feedback.

3. adenylate cylase is here to convert ATP to cAMP. Its inactivation will give positive feedback to glucagon signaling pathway to produce more cAMP.

4. positive feedback

5. this process enhance glycogenolysis process so it will give negative feedback to the glucagon signaling pathway for less production of glucose.

6. positive feedback.

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.