Glycogen

Question 1

What linkages does glycogen have?

Answer 1

1 to 4

1 to 6

Question 2

Which is longer? glycogen or starch

Answer 2

Glycogen

Question 3

What bond forms between 2 glucose?

Answer 3

Glyosidic Bond

Question 4

Describe the structure of glycogen

How many glucose per chain?
When does branching occur?

Answer 4

3D helical structure

12-14 glucose
Branch occurs every 8-12 glucose

Question 5

Glycogen granules are made up by how many molecules?

Answer 5

20-40

Question 6

Where is glycogen stored and how much % mass does it make up?

Answer 6

Free in the cytoplasm

Up to 10% of the liver mass
1-2% of the muscle

Question 7

Describe the first 2 steps in glycogenolysis

Answer 7

Glycogen + Pi cofactor -> G1P ( catalysed by glycogen phosphorylase)

G1P-> G6P(catalysed by phosphoglucomutase)

Question 8

What is the general equation for phosphorolysis?

Answer 8

R-O-R’ + HOPO3^2–> R-OH + R’-OPO3^2-

Question 9

Why do we use phosphorolysis?

Answer 9

This doesnt use ATP

Glycogen to glucose to G6P requires ATP

Question 10

Name the 3 glycogen isozymes

Answer 10

Muscle (mGP)
Brain (bGP)
Liver (lGP)

Question 11

Describe the structure of the phosphorylase active site

Is there a co factor?

Answer 11

Monomer of Homodimer
Deep cleft to active site in the centre
Pyridoxal phosphate(PLP)
prosthetic group

Question 12

Phosphorylase is P_____ and R_____

Answer 12

Phosphorylase is processive and reversible

Question 13

MAKE CARD ON PHOSPLOYLASE MECHANISM - SLIDE 6

Answer 13

XX

Question 14

What is the benefit of glycogen having procession and a branched structure?

Answer 14

Rapid mobilisation of Glc

Question 15

What are two things that phosphorylase can’t do?

Answer 15

Break 1-4 within 4 units of the branch point

and 1-6 linkages

Question 16

Describe branched points of glycogen catabolism

Answer 16

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,

Question 17

G1P -> G6P via phosphoglucomutase

Describe the reactants and products in this 2 step reaction

Answer 17

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

Question 18

Describe in muscles how glycogen is used

Answer 18

Glycogen to glycolysis to ATP

Question 19

Describe in the liver how glycogen is used

Answer 19

Glycogen to gluconeogenesis to increase blood glucose

G6P to glucose for the brain mostly

Question 20

The reactions in glycogen anabolism don’t usually happen-why?

Answer 20

The [Pi] is greater than [G1P] and there is cooperative binding of the Pi

Question 21

Describe glucose activation.

Answer 21

Glucose-1-phosphate + Uridine Triphosphate -> UDP-glucose with PPi

Question 22

How does UDP-glucose bind to glycogen?

Answer 22

Only forms 1-4 bonds so cant start chains if glycogen not present

Question 23

What is glycogenin?

Answer 23

Primer extended by Glycogen Synthase

Builds initial 8 unit primer chain

Question 24

What is the role of the branching enzyme in glycogen anabolism

Answer 24

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