glycogen metabolism

Question 1

what happens to glucose once it’s phosphorylated within the cell?

Answer 1

can:

• undergo synthesis for glycogen
• undergo pentose phosphate pathway
• can undergo glycolysis and CA cycle

Question 2

describe the structure of glycogen

Answer 2

branched polymer of alpha-1,4 and alpha 1,6 linkages

Question 3

how does glycogen differ from fat in terms of its utility?

Answer 3

unlike fat, glycogen can be metabolized for energy

Question 4

where do synthesis and degradation of glycogen occur (on the molecule)?

Answer 4

at the non-reducing end of the polymer

Question 5

what is phosphoglucomutase and what does it do? is the action reversible?

Answer 5

enzyme involved in degradation of glycogen
coverts G-6-P to G-1-P
creates a glucose-1,6-bisphosphate intermediate
reaction is reversible

Question 6

what are the steps in glycogen synthesis?

Answer 6

UDP-glucose pyrophosphorylase attaches G-1-P to UDP
Glycogen synthase coverts UDP-glucose to glylcogen and then removes UDP
branching enzyme makes glycogen branched

Question 7

what is UDP-glucose pyrophosphoylase? is it reversable?

Answer 7

first step in glycogen metabolism
attaches G-1-P to UDP
practically irreversible cause fast

Question 8

what are the components of debranching enzyme? what do they do?

Answer 8

glucosyl transferase transfers residues to non-reducing end of glycogen
alpha-1,6-glucosidase hydrolyzes alpha-1,6 linkage at branch’s base
both part of degradation of glycogen

Question 9

what does glycogen phosphorylase do? how is it regulated?

Answer 9

part of degradation of glycogen
adds P to make G-1-P
regulated allosterically through phosphorylation

Question 10

what is pyridoxal phosphate made from? where is it found?

Answer 10

made from vitamin B6

covalently bound to a lysine in glycogen phosphorylase via schiff-base linkage

Question 11

what does G-6-phosphatase do? where?

Answer 11

coverts G-6-P to glucose

usually in ER lumen of liver

Question 12

what is the effect of epi on glycogen metabolism?

Answer 12

1: epi activates cAMP-dependent protein kinase via GCPR signaling cascade
2: protein kinase phosphorylates phosphorylase kinase => activation
3: phosphorylase kinase activates phosphorylase-b to phosphorylase-a

Question 13

how does AMP affect glycogen metabolism?

Answer 13

allosterically activates phosphorylase-b in muscle

activates b form from T to R state

Question 14

what is the effect of ATP and G-6-P on glycogen metabolism?

Answer 14

both allosterically inhibit phosphorylase-b in muscle

change phosphorylase-b into T state