Question

When secreted in the human body, the hormone glucagon causes rapid degradation of glycogen in liver cells. This mobilization of glycogen is accomplished though a signaling pathway. What is the proper temporal sequence of the following steps in this reaction cascade?

A - displacement of GDP with GTP on the a-subunit of the G-proteins

B - phosphorolysis of glycogen

C - dissociation of the regulatory subunits activates protein kinase A

D - phosphorylation of glycogen phosphorylase

E - glucagons binds to a specific, transmembrane receptor

F - formation of cyclic-AMP by adenylyl cyclase


a. E-C-A-F-D-B


b. E-F-A-C-D-B


c. E-C-A-F-B-D


d. E-A-F-C-B-D


e. E-A-F-C-D-B

Answer 1

The correct sequence for the steps in the glucagon-signaling pathway that leads to glycogen degradation in liver cells is: glucagon binds to receptor, G-protein activation, cAMP formation, protein kinase A activation, phosphorylation of glycogen phosphorylase, and finally glycogen phosphorolysis.

Step-by-step explanation:

When the hormone glucagon is secreted in the human body, it initiates a signaling pathway resulting in the degradation of glycogen in liver cells through a series of steps. The correct temporal sequence for the steps in this signaling pathway is as follows:

1. Glucagon binds to a specific, transmembrane receptor (E).
2. Displacement of GDP with GTP on the a-subunit of the G-proteins (A).
3. Formation of cyclic-AMP by adenylyl cyclase (F).
4. Dissociation of the regulatory subunits activates protein kinase A (C).
5. Phosphorylation of glycogen phosphorylase (D).
6. Phosphorolysis of glycogen (B).

This sequence leads to the mobilization of glycogen, converting it into glucose which can then be used as energy or released into circulation.