Describe the regulation of glycogen synthase and glycogen phosphorylase in the s

Question

Describe the regulation of glycogen synthase and glycogen phosphorylase in the synthesis and degradation of glycogen in the liver and skeletal muscle

5: Describe the mechanism by which epinephrine induces glycogenolysis in the skeletal muscle

6: Describe the regulation of hexokinase/glucokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase in glycolysis

6: Describe the regulation of glycogen synthase and glycogen phosphorylase in the synthesis and degradation of glycogen in the liver and skeletal muscle

6: Compare and contrast glucokinase and hexokinase

Explanation / Answer

5)Regulation of Glycogen Synthase:Regulated byProteinKinase A(when phosphorylates glycogen synthase-> causes to be inactive),Protein Kinase C(when phosphorylatesglycogen synthase-> causes to be inactive),Calmodulin-dependent protein kinase(when phosphorylates glycogensynthase-> causes to be inactive),Phosphorylase Kinase(when phosphorylates glycogen synthase-> causes to beinactive) .

.Regulation of Glycogen Phosphorylase:Regulated byProtein Kinase A(when phosphorylated then active andbreaks down glycogen),Phosphorylase Kinase(whenphosphorylated then active and breaks down glycogen),Calcium-calmodulin(which activates Phosphorylase Kinase,and therefore activates glycogen phosphorylase), High levelsof AMP activates glycogen phosphorylase.

The two are opposites of one another with makes sense due to the fact then when glycogen is being degraded it is NOT also going to be synthesized in the cell. Since muscle DOES NOT have glucagon receptor, thus glucagon has no effect on the utilization and levels of glycogen. Muscle glycogen levels and usage vary in respect to the feeding and fasting state of the body since glucose is not able to leave the skeletal muscle like it does in the liver.

6)1) Epinephrine binds to a g-protein coupled receptor which then binds GTP and activates adenylate cyclase.

2) Adenylatecyclase then converts ATP to cAMP which then bindsregulatory subunit of Protein Kinase A to generate an activeProtein Kinase A .

3) Active Protein Kinase A phosphorylatesanother glycogen kinase (phosphorylase kinase) and oncephosphorylated, phosphorylase kinase is ACTIVE.

4)Phosphorylase Kinase then phosphorylates glycogenphosphorylase B into its active form which then facilitates   it and decreases its activity.

7)Hexokinase – low Km, low VmaxoGlucoseGlucose 6-phosphateoG6P inhibits hexokinaseoGKRP regulates theseoNeeds ATP.

Glucokinase – high Km, high Vmax; in liveroGlucoseglucose 6-phosphateoGlycolysis continues in liver even when energy is high so anabolic pathways can occuroNeeds ATP.

PFK-1 has 6 different allosteric binding sites.
1. MgATP (inhibitory)
2. Citrate/other anions (inhibitory)
3. AMP (activation)
4. Fructose 2,6-bisphosphate (activation)
5. other bisphosphates
6. other bisphosphates
Pyruvate kinase
Induced by Ffructose 1,6-bisphosphate
Inhibited by ATP

8)Hexokinase and Glucokinase are both enzymes that phosphorylate glucose as Glucose-6-P, which "traps" the sugar molecule in the cell it is in G6P cannot diffuse out of cell.Hexokinase is located in all tissues, whereas Glucokinase is only located in the liver and pancreatic beta cells. Hexokinase has a low Km and low Vmax, which means that it has a high affinity for glucose it will bind easily to glucose molecules it encounters but a low v-max, so even during fasting, when glucose levels are low, it is saturated. This is beneficial for tissues such as the brain and muscle, which require glucose at all times, but its relatively low activity prevents it from clearing large amounts of glucose from the blood. Glucokinase, on the other hand, has a high Km and a High v-max, which allows the liver to effectively remove large amounts of dietary glucose from the blood, and prevents large amounts of glucose from entering systemic circulation following a carbohydrate-rich meal. Glucokinase and Hexokinase are rate limiting enzymes for glycolysis, and are stimulated by insulin.....

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