Flashcards in  Lecture 8: Glycogen Metabolism Deck (87)
Liver GP is inactivated and moves to tense states under what conditions?
Major inactivator of Liver (a) GP?
Glu binds to active site and stabilizes conformation in the inactive T state.
Makes sense...when BG levels are high, there's no need for glycogen breakdown.
Muscle GP (b) is activated under what conditions?
Low energy states
Activated by AMP...
This makes sense b/c muscle contraction ATP converted to AMP by myosin and adenylate kinase signaling the GP to breakdown glycogen
AMP GPb activator mechanism:
Binds to active site and stabilizes conformation of the b in the active R state
What are 2 negative allosteric regulator (inhibitors) of GP b (muscle)?
ATP and gluc-6-phosphate
Under norm physiological conditions GP inactive b/c of inhibitory effect of ATP and Gluc-6-phosphate
What role does phosphorylation play in glycogen phosphorylase?
How is it initiated?
Phosphorylation of a single serine residue converts GP b to GP a
Conversion initiated by hormones
Phosphorylation of GP is carried out by what enzyme,?
Phosphorylase kinase (PK)
How is phosphorylase kinase partially activated?
4 Ca++ ions partially activate PK
4 Ca++ ions and 8 Phosphates fully activates PK
What results when Pohsphoylase kinase is fully active?
Phosophorylase b converts to phosphorylase a
But requires 2 ATP
Wha hormone is released under low [BG] conditions
Muscle activity releases what hormone?
Glucagon and epinephrine are mediated via:
Both of these hormones signal:
via G protein coupled receptors (GPCR)
Signal glycogen breakdown
Glucagon and epinephrine, can they pass the plasmalemma?
No they are peptide hormones that act on the GPCR's
When does glycogen breakdown stop?
When the hormone (glucagon or Epi) shuts down
PK and GP are DEphosphorylated =inactivated
When synthesis of glycogen is promoted
Liver and muscle forms of GP are products of separate genes what is this term called?
Liver vs. muscle GP
DIFFER: in their sensitivities to regulatory molecules
Both are activated by phosphorylation by phosphorylase kinase and inhibited by ATP and G6P
Muscle GP is allosterically activated by
Liver GP is inactivated by:
Inactivated by glucose and unaffected by AMP
Mutations in liver GP causes
Mutaiton in muscle GP causes:
3 key events in glycogenesis:
1. Trapping and activating of glucose.
2. Elongation of glycogen polymer
3. Branching of glycogen chains.
In the cytosol of hepatocytes and muscle cells catalyze phosphorylation of glucose to glucose-6-phosphate.
This traps glucose in theses cells.
Glucokinase / hexokinase
Reversible isomerizes G-6-P to G-1-P
Transfers the G-1-P to uridine triphosphate which generates UDP-glucose
Uridine diphosphate (UDP)-glucose pyrophosphorylase
Active form of glucose
What is the significance of the Breakdown of pyrophosphate to Pi w/ UTP and glycogenesis?
generates energy and drives the RXN forward
Preexisting short glycogen polymer serves as a primer to which glucose units are added
Primer formation done by glycogenin
This is completed by the transfer of glucose from UDP-glucose onto a non-reducing end of glycogen chain. What enzyme comlpletes this?
Rate limiting rx of glycogenesis
Forms alpha-1,4-glycosidic bonds btw glucose molecules.