Question

Discuss how adrenaline binding to a receptor on hepatocyte cell can ultimately lead to the breakdown of glycogen.
In your answer include
1. Receptor activation at the. Plasma membrane and
2. Single transduction in Cytoplasm leading to activate of glycogen phosphorylase.

can u tell me please in briefly because it is 20 marks questions I need and in briefly plzz

Answer 1

Epinephrine (adrenaline), is a catecholamine derived from tyrosine, from the adrenal medulla. Glucagon and adrenaline trigger the breakdown of glycogen. Muscular activity leads to the release of adrenaline and it stimulates glycogen breakdown in muscle and liver.

A signal transduction pathway in a liver cell :-

1. When the hormone binds to an epinephrine receptor on the cell surface, it triggers the receptor to change shape. The receptor is thus converted to its active form.
2. The activated receptor triggers a cascade of events within the cell. Firstly, it activates a G protein which then binds to the activated receptor. It releases GDP and takes up a molecule of GTP.
3. Then the G protein is released from the receptor and splits into two parts. One part is activated and continues the signaling cascade. Then, the hormone also leaves the receptor. After that the receptor reverts to its inactive form.
4. The G protein activates an enzyme called adenylyl cyclase that converts a large number of ATP molecules into signaling molecules, called cyclic AMP (cAMP).
5. G protein cleaves GTP and inactivates itself. Then the subunits reassociate. With the G protein no longer attached, the adenylyl cyclase turns off and can no longer convert ATP into cAMP.
6. The cAMP molecules binds to an enzyme called protein kinase and continue the signaling cascade. Protein kinase A separate into two catalytically active subunits.
7. These subunits activates phosphorylase kinase by adding phosphate groups to phosphorylase kinase.
8. Phosphorylase kinase then phosphorylates and activates glycogen phosphorylase.
9. Activated glycogen phosphorylase breaks down glycogen into glucose molecules. During the process, the enzyme adds a phosphate group to each of the glucose subunits.
10. Another enzyme removes the phosphate groups from the glucose molecules.
11. Glucose molecules can be transported across the plasma membrane of the cell after the removal of phosphate groups.