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10 Cards in this Set

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Generally describe the reactions required for glycogen synthesis. Include enzymes involved.
UDP-Glucose Pyrophosphorylase transfers Uridine-P to glucose-1P to create UDP-glucose + PPi. Hydrolysis of PPi by pyrophosphatase pulls reaction forward.

Glycogen synthase then joins glucose to glycogen. UDP is a relatively good leaving group and will be more favorable than having phosphate as a leaving group.
Describe the effect of glycogen synthesis on stereochemistry. Elaborate on the mechanism. What are the enzyme's substrate requirement? Why do these requirements make sense?
Stereochemistry is reatined (everything stays below glucose ring).
Done by SN2 reactions (2 inversions = retained).

UDP of glucose is attacked by Asp forming an intermediate (UDP is kicked off and charged), then UDP will remove H from glycogen, and glycogen will attack glucose and release Asp (second inversion)

Requires 4 glucoses in a row so it can bind glycogen and make more glycogen so doesn't have to "hop on and off".
Describe the role and mechanism of glycogenin.
Similar activity to glycogen synthase except it can start off with a single UDP-glucose. Does so by having Tyr attack glucose-UDP and kick off UDP. Glucose then will attack another UDP-glucose, thus polymerizing glucoses. Will stop at 7 glucoses and then glycogen synthase will take over.

Also employs double displacement to maintain stereochemistry, with transfer to Asp, etc.
What are the mechanistic differences (general) between debranching and branching enzymes?
Debranching break a-1,4 make a-1,4 and a-1,6 broken by hydrolysis via a-1,6-glucosidase

Branching breaks a-1,4 and makes a-1,6
What is the carrier for glucose in branching enzymes? How does it work (generally)?
Asp comes in, attacks, takes off, and asp gets attacked to put it back on transferase. Both cleavage and bond synthesis occur in same active site.
What would be the effect of epinephrine on glycogen breakdown?
Epinephrine would activate glycolysis; beta-adrinergic receptor would activate PKA and thus increase glycogen breakdown
What is the effect of epinephrine on glycogen? Explain.

Which principle is this an example of?
PKA activates phosphorylase kinase, who phosphorylates phosphorylase b-->phosphorylase a (active)

PKA phosphorylates synthase from a to b (inactive)

Reciprocal Regulation
What molecules does protein phosphatase 1 (PP1) affect? Describe its mechanism.

How is it activated/inhibited?
Phosphorylase
Phosphorylase kinase
Synthase

PP1 must be near glycogen, so binds to Rgl who is an adapter protein bound to glycogen and acts to bring PP1 near glycogen. Then has phosphatase activity.

PKA (epi binding): phosphorylates Rgl which breaks interaction between Rgl and PP1 and phosphorylates PP1-inhibitor protein (activating it).

Activate:
Insulin-->RTK-->cascade activates insulin-sensitive protein kinase which P's Rgl making it active again.

Liver: when glucose high in liver (glucose low in body), phosphorylase a goes to T-state and releases PP1 who can now go remove a phosphate from a phosphorylase a.
Since there's a lot more phosphorylase than PP1, what must be required for effective functioning of PP1?
Need more phosphorylase driven into T state to get release of PP1, which requires quite a bit of glucose!
What activities (products) would allow Phosphorylase kinase to be partly active? Fully active?
PKA: P , Ca+ (muscle contraction), BOTH give fully active phosphorylase kinase.