Glycogen Flashcards
What linkages does glycogen have?
1 to 4
1 to 6
Which is longer? glycogen or starch
Glycogen
What bond forms between 2 glucose?
Glyosidic Bond
Describe the structure of glycogen
How many glucose per chain?
When does branching occur?
3D helical structure
12-14 glucose
Branch occurs every 8-12 glucose
Glycogen granules are made up by how many molecules?
20-40
Where is glycogen stored and how much % mass does it make up?
Free in the cytoplasm
Up to 10% of the liver mass
1-2% of the muscle
Describe the first 2 steps in glycogenolysis
Glycogen + Pi cofactor -> G1P ( catalysed by glycogen phosphorylase)
G1P-> G6P(catalysed by phosphoglucomutase)
What is the general equation for phosphorolysis?
R-O-R’ + HOPO3^2–> R-OH + R’-OPO3^2-
Why do we use phosphorolysis?
This doesnt use ATP
Glycogen to glucose to G6P requires ATP
Name the 3 glycogen isozymes
Muscle (mGP)
Brain (bGP)
Liver (lGP)
Describe the structure of the phosphorylase active site
Is there a co factor?
Monomer of Homodimer
Deep cleft to active site in the centre
Pyridoxal phosphate(PLP)
prosthetic group
Phosphorylase is P_____ and R_____
Phosphorylase is processive and reversible
MAKE CARD ON PHOSPLOYLASE MECHANISM - SLIDE 6
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What is the benefit of glycogen having procession and a branched structure?
Rapid mobilisation of Glc
What are two things that phosphorylase can’t do?
Break 1-4 within 4 units of the branch point
and 1-6 linkages
Describe branched points of glycogen catabolism
Phosphophorylase makes 4 glycosyl unit branch w/ 8 Pi cofactor to produce G1P
Transferase transfers 3 glycosyl units to the core so branch =1
Alpha-1,6-Glucosidase hydrolysis the single branch glucose to free glycose,
G1P -> G6P via phosphoglucomutase
Describe the reactants and products in this 2 step reaction
Enzyme has Serine with OPi
G1P has P on carbon 1
The P from Serine swaps place with H on Carbon 6 and becomes Serine OH
Then serine OH becomes Serine OPi again taking the P from carbon 1
Describe in muscles how glycogen is used
Glycogen to glycolysis to ATP
Describe in the liver how glycogen is used
Glycogen to gluconeogenesis to increase blood glucose
G6P to glucose for the brain mostly
The reactions in glycogen anabolism don’t usually happen-why?
The [Pi] is greater than [G1P] and there is cooperative binding of the Pi
Describe glucose activation.
Glucose-1-phosphate + Uridine Triphosphate -> UDP-glucose with PPi
How does UDP-glucose bind to glycogen?
Only forms 1-4 bonds so cant start chains if glycogen not present
What is glycogenin?
Primer extended by Glycogen Synthase
Builds initial 8 unit primer chain
What is the role of the branching enzyme in glycogen anabolism
Binds to chains 11+ long
Cuts off heptamer of glucose units
Reattaches heptamer via α(1→6) bond
Reattachment site >4 units from existing branch
