Glycogenolysis Flashcards
1
Q
Glycogenolysis steps in the liver
A
- Glucagon receptor receives glucagon, and beta-adrenergic receptor receives catecholamines from adrenal gland
- Receptors stimulate adenylate cyclase converting ATP to cAMP
- cAMP activates protein kinase A
- Protein kinase A stimulates the phosphorylation of phosphorylase kinase which simultaneously inhibits glycogen synthase from making more glycogen AND activates glycogen phosphorylase (which breaks down 1,4 linkage of glycogen into glucose-1 phosphate)
- alpha-1,6 linkage breakdown (by alpha 1,6-glucosidase (debranching enzyme))
2
Q
alpha 1,6 linkage breakdown
A
Uses debranching enzyme (alpha-1,6 glucosidase)
1. Transfers a block of 3 residues to the non-reducing end
2. Cleaves single remaining alpha-1,6-linkage to directly yields a glucose
3
Q
Liver glycogen breakdown routes
A
- Glucose released into blood (main function). Able to do this because GLUT 2 transporter is bidirectional. Both types of glycogen can go into the blood. alpha 1,4 glycogen can get into blood from glucose-6-phosphatase.
- Fuel for glycolysis. alpha-1,4 glycogen is used for this.
4
Q
Where does untrapping of glycogen occur?
A
Endoplasmic reticulum
As untrapping occurs, and accumulates, the concentration gradient will cause the transport of it back into the blood through GLUT 2
5
Q
Glycogenolysis in muscle
A
- beta-adrenergic receptor receives catecholamines from the adrenal gland (as a response to stress of exercise). There is no glucagon receptor
- Receptor stimulate adenylate cyclase that converts ATP to cAMP
- cAMP used to produce Protein Kinase A (intercellular cascade)
- Protein kinase A (OR muscle contraction releasing Ca2+; skips previous steps) stimulates the phosphorylation of phosphorylase kinase which simultaneously inhibits glycogen synthase from making more glycogen AND activated glycogen phosphorylase (which breaks down 1,4 linkage of glycogen)
- All glycogen that is broken down is used for glycolysis in the liver
