glycogen - lecture 2 Flashcards
what is the structure of Glycogen?
α(14) linked glucose
α(16) linked branch points
How is the inner region of glycogen composed?
B-chains, two branch points
How is there outer region of the glycogen composed?
A-chains, not branched
What is the typical size of glycogen structure?
typically there are around 1500 glucose residues
why are all the outermost chains unbranched?
Makes the glucose easily accessible
Outermost tier always contains 34.6% of the glucose of the glycogen molecule
What is glycogenin?
homodimeric protein found t the core of a glycogen molecule
What is the role of glycogenin?
extends the gluten chain by up to 9 additional UDP - glucose. Only at this point does glycogen synthesis act
Where is the first glucose added onto in Glcogenin?
first glucose added to Try195
What are the activated precursors that Glycogenin and Glucose synthase use?
UDP-glucose – in eukaryotes
ADP-glucose used in bacteria and plants [starch]
What does UTP and glucose -1 - phosphate got to?
UDP -glucose
What is the enzyme that catalyse the synthesis of UDP - glucose?
UDP-glucose pyrophosphorylase
What happens when the UDP - glucose as joined together?
glycosyl transfer with release of UDP
What is the mechanism for the synthesis of UDP - GLUCOSE
double SN2?
SNi? – latest evidence is for this
what is the name of the enzyme that causes branching in glycogen synthesis?
amylo-(1,4 1,6)transglycosylase
How is a branch formed?
A terminal chain section of ~7 residues is transferred to the C6-OH of another glycogen chain
What are the 3 enzymes that cause degradation of glycogen?
Glycogen phosphorylase
Glycogen debranching enzyme
Phosphoglucomutase
What does Glycogen Phosphorylase do?
- catalyses Glycogen phosphorolysis to yield glucose - 1 - phosphate
What is the limiting factor I regards to Glycogen phosphorylase degradation?
Can only get to within 5 residues of a branch point
What is significant about the debranching enzyme in eukaryotes?
eukaryotic enzyme is bi-functional
What are the two enzymes that make up the debranching enzyme function
Transferase and α-1,6 glucosidase
What does Phosphoglucomutase do?
converts G-1-P into G-6-P
G-6-P enters glycolysis
What happens when glucose is plentiful?
G-6-P is formed by hexokinaseChanges equilibrium positionPhosphoglucomutase converts G-6-P in to G-1-PG-1-P is substrate to form UDP-glucose for glycogen synthesis
What are the rates of glycogen synthesis/degradtion In liver?
The capacity are about equal
What are the rates of glycogen synthesis/degradation in muscles
degradation can happen about 300 times faster than synthesis
