Glycogen Synthesis and Degradation Flashcards
What two hormones maintain blood glucose?
Insulin and glucagon
How does glycogen convert to blood glucose?
Glycogen → Glucose 6-P → Pi + glucose → Blood glucose
What does branching of glycogen do?
More branches mean more ends for glucose to be released more
it increases stability and solubility
creates a large number of terminal residues
Its the site of action for enzymes
What are the two types of glycogen linkages?
a-1->4 glycosidic linkage
a-1->6 glycosidic linkage
What are the first 3 reactions in turning glucose to glycogen?
1) Diet -> glucose
2) Glucose -> glucose 6 phosphate
3) Glucose 6 phosphate -> Glucose 1 phosphate
How to turn Glucose 1 phosphate to UDP glucose?
Glucose 1 phosphate + UTP -> P-Pi + UDP glucose
How UDP glucose can form a glycogen chain?
1) UDP glucose + Glycogenin (protein primer) -> UDP + Glucose with protein
2) They can then form a1->4 bonds as the process continues
3) Branch points introduced in glycogen allow branching enzymes to work and a1->6 to be made
4) Branching enzyme introduces a new site for new chains
5) Glycogen synthase enzyme extends straight chains, so glycogen chains are formed
How do glycogen chains become glycogen?
Glycogen chain + Pi -> glucose 1-P + Glycogen (short chain)
How to remove glucose from glycogen?
Debranching enzymes can be used to hydrolyse the 1->6 glycosidic link. they are then further degraded by glycogen phosphorylase acting on 1->4 links
How to form free glucose from glycogen breakdown?
Glycogen breakdown by phosphorylase results in production of glucose 1-P -> Glucose 6-P -> glucose with enters the blood
How to activate and inactivate glycogen synthetase?
To activate glycogen synthetase you add protein phosphatase
To inactivate glycogen synthetase you add protein kinase
How is glycogen degraded in the muscle?
During muscular contraction, Ca2+ is released into the sarcoplasmic reticulum
Ca2+ binds to the calmodulin domain of glycogen phosphorylase kinase and activates the enzyme.
Glycogen is then degraded providing energy for muscle contraction
What happens in prolonged exercise?
ATP concentrations are reduced and AMP increased so as AMP is an allosteric activator the glycogen degradation continues without hormonal interaction
ATP is an allosteric inhibitor so when levels are high, glycogen breakdown stops
