Question

Write out by hand the steps of the signal transduction pathway starting from binding of insulin to its receptor on a liver cell, leading to inhibition of glycogenolysis in that tissue. Include all steps in detail and hand write out this process. Look for hints as to the amount of detail on the Note Outlines with additional notes associated with Module 8. This also requires some review of module 5 on glycogen metabolism. Also remember insulin my cause multiple effects leading to this outcome.  

Answer 1

Inhibition of glycogenolysis by insulin would involve the dephosphorylation of active glycogen phosphorylase a into inactive phosphorylase b and the steps as as below:

1. Upon binding with the insulin receptor on the liver cell, insulin activates protein phosphatase 1 (PP1) and the enzyme phosphodiesterase.
2. Phosphodiesterase breaks down cAMP to AMP as a result of which the activity of PKA to phosphorylate and activate glycogen phosphorylase is inhibited.
3. Phosphatase 1 dephosphorylates active glycogen phosphorylase A to inactive glycogen phospharylase B thereby inhibiting glycogenolysis.

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