Glycogen Breakdown

Front 1

Why is 10% of liver devoted to glycogen and only 2% in muscle?

Back 1

Liver devoted to glycogen and goes toward whole body; more muscle than liver, but muscle is greedy, so it keeps it!

Front 2

Difference between a-1,4 and a-1,6 linkage?

Back 2

1,6 linkage connects branch glucose to another branch, 1,4 connects glucose to other glucoses on same branch.

Front 3

Why is there so much branching in glycogen?

Back 3

More branching means more ends. Glucose removed from branch ends. More ends means more efficient production of glucose.

Front 4

Which glucose is removed?

Back 4

Nonreducing glucose

Front 5

Site of action of glycogen phosphorylase? General method? Advantage?

Back 5

1, 4 positions; phosphorylation because glucose eventually phosphorylated in glycolysis (saves ATP as opposed to hydrolyzing) and block off active site from H2O.

Front 6

Affect of glycogen phosphorylase on stereochemistry? How is this achieved? Describe mechanism.

Back 6

Retained stereochemistry via SN2 reaction (reaction occurs from bottom of ring, so not racemic)
Pirodoxyl phosphate (PLP) is coenzyme in glyc phosphorylase. Interacts with Phosphate and lys, phosphate interacts with glycine and lysine and PLP (making for a more acidic H).
Gives up H to position 1 Oxygen, freeing non-reducing glucose while forming carbocation. Glucose then bonds to PLP phosphate. Phosphate enters to knock off p-glucose (G-1P) and regenerate original PLP.

Front 7

Role of LYS, ARG, GLY in glycogen phosphorylase? Effect of conservative mutation? Why?

Back 7

Serves as wall of bulky amino acids to pack tightly and surround G-1-P. Keep water out.
Mutations disrupts barrier, results in loss of activity (enzyme only active in ONE conformation) and increase in hydrolysis.

Front 8

How is G-1,P made into a usable form? Mechanism?

Back 8

Phosphoglucomutase: G-1PG-6P

Ser-P transferred to 6-posn on glucose-1P. 1-P released and bound to serine.

Front 9

Specific requirement of glycogen phosphorylase functionality? Advantage?
How is this remedied? Describe mechanism.

Back 9

Must have at least 4 glucoses before branchpoint. Keeps GlycPase from hopping on and off.


Phosphorylase will phosphorylize all glucose monomers further than 4 glucoses away from branchpoint (deals with 1,4 linkage).
Transferase moves 3 of the 4 remaining glucoses to a longer glucose branch.
a-1,6-glucosidase hydrolyzes last glucose at 1,6 linkage (doesn’t waste ATP)

Front 10

Differences between phosphorylation states of glycogen phosphorylase?

Back 10

Phosphorylase b (no phosphate) favos T state (inactive), phosphoylase A (phosphorylated) favors R state (active site exposed)

Front 11

How does glycogen phosphorylase differ in liver and muscle?

Back 11

Muscle: Phos b, favors T state with ATP or Glu-6P, R state with AMP
Liver: Phosphorylase a, Favors T with high glucose