Question

26.  Complete three and only three of the following:

1. Outline the summary of events in the β-adrenergic receptor signal transduction pathway.2.
2. Define the Cooperativity Index (AKA Saturation Ratio) and review its significance with regard to the function of enzymes and ligand binding proteins.3.
3. Discuss hormonal regulation of glycogen synthesis and breakdown.4
4. Give a summary of hormonal regulation of triglyceride metabolism in adipocytes.5.
5. Discuss the choice of substrate concentrations for enzyme kinetic experiments to determine K_M. To determine V_max.6.
6. Review hormonal regulation of gluconeogenesis and glycolysis in liver.

Answer 1

Glycogen breakdown and synthesis are reciprocally regulated by a hormone-triggered cAMP cascade acting through protein kinase. protein kinase A adds a phosphoryl group to glycogen synthase, which leads to a decrease in enzymatic activity.This mechanism prevents glycogen from being synthesized at the same time that it is being broken down. Changes in enzymatic activity produced by protein kinases are reversed by protein phosphatases.

The changes in enzymatic activity produced by protein kinases are reversed by protein phosphatases. The hydrolysis of phosphorylated serine and threonine residues in proteins is catalyzed by protein phosphatases. The enzyme protein phosphatase 1, plays key roles in regulating glycogen metabolism. PP1 inactivates phosphorylase kinase and phosphorylase a by dephosphorylating these enzymes. PP1 decreases the rate of glycogen breakdown: it reverses the effects of the phosphorylation cascade. PP1 also removes the phosphoryl group from glycogen synthase to convert it into the much more active a form. Hence, PP1 accelerates glycogen synthesis. PP1 is yet another molecular device for coordinating carbohydrate storage.