Lecture 1/22 - Glycogen metabolism Flashcards
Glycogen mobilization
Also called glycogenolysis
Glycogen phosphorylase
degrades glycogen from the nonreducing ends of the glycogen molecule. Uses energy from hydrolysis to add phosphate (onto 1 C)
Which end do glucose monomers come from?
non-reducing ends
4 enzymes in glycogen mobilization
- Glycogen phosphorylase
- Transferase moves trios onto a non-reducing end of another chain
- alpha-1,6 glucosidase clips the branch point (but doesn’t add a phosphate)-debranching enzyme
- glucomutase (moves the phosphate from 1 to 6)
Where does the phosphate come from after glycogen is hydrolyzed by glycogen phosphorylase?
From cytoplasm, not ATP
Where does glycogen phosphorylase stop
4 from end of branch point (including the branching glycogen)
Glucomutase
Moves a 2nd phosphate onto glucose, making glucose1,6-bisphosphate, then accepts the 1 phosphate, leaving glucose-6-phosphate
Role of insulin
Drive glucose into cells
Role of glucagon
Tells the liver to raise glucose in the blood (favor glycogenolysis)
Epinephrine
Tells muscle to get glucose out of its glycogen? It is a small modified amino acid.
How is glucose phosphorylase regulated?
By allosteric inhibition and covalent modification
Is glycogen phosphorylase generally on or off in the liver
On (R state, phosphorylated)
How does high blood sugar inhibit phosphorylase
Glucose gets into the liver via high Km transporter, then allosterically inhibit phosphorylase (stabilize T state)
Is glycogen phosphorylase generally on or off in the muscle
Off (T state, can be activated by high [AMP] in low energy charge).
Phosphorylase kinase
Actives glycogen phosphorylase by PKA or Ca+
