Glycogen metabolism

Question 1

When glucose is from glycogen, does it provide enough for a day?

Answer 1

yes

Question 2

Tell me the glycogen composition?

Answer 2

• branched polymer of glucose (macromolecule)
• Main chan is alpha (1–>4) linkage with glycosidic bonds
• side chain is alpha (1–>6) linkage with glycosidic bonds

Question 3

Tell me about glycogen’s structure?

Where branches occur?

diameter?
How many glucose molecules per glycogen?

etc.

Answer 3

• Helical structure- coiled chain
• 12-14 glucose/ chain
• Branch occurs every 8-12 glucoses (there will be side chains coming off these also)
• 3D branching structure
• Up to 120,000 glucose per glycogen molecules
• Roughly 10-40 nm diameter

Question 4

Tell me about glycogen storage?

The percentage kept in liver and muscle and why this ratio?

Answer 4

• Glycogen granules (=20-40 molecules)
• Up to 10% of liver mass (liver glycogen store is for the entire body)
• 1-2% of muscle (smaller store as only for muscle)

Question 5

Tell me the steps to Glycogenolysis and the enzymes used…

Answer 5

Question 6

What do phosphorylases use to make or break bonds?

Answer 6

Pi

Question 7

Compare hydrolysis and Phosphorolysis

Answer 7

Hydrolysis: R-O-R’ + HOH –> R-OH + R’-OH

Phosphorolysis: R-O-R’ + HOPO₃^2- –> R-OH + R’-OPO₃^2-

(Both use molecules with an oxygen bridge)

Question 8

What are all the different things Pi can be called/ referred to as?

Answer 8

Pi = HPO₄^2- = HOPO₃^2- = orthophosphate = inorganic phosphate

Question 9

Why is phosphorolysis used?

Answer 9

Glycogen –> glucose –> Glucose-6-phosphate (requires ATP). so dont waste ATP then

Question 10

Tell me the cleft to phosphorylases active site

Answer 10

Deep cleft to active site- Pyridoxal phosphate (PLP) prosthetic group.

Question 11

Whats needed for the enzyme Phosphorylase to work?

Answer 11

Vitamin B6

Question 12

What are the 3 isozymes that are all referred to as phosphorylase?

Answer 12

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

Question 13

Whats phosphorylase a monomer of?

Answer 13

Homodimer

Question 14

Phosphorylase is processive, what does this mean?

Answer 14

Phosphorylase is processive- carry on and do next reaction without substrate being released. As long as phosphate ions break the glycosidic bond

Question 15

What does procession and a branched structure of phosphorylase mean?

Answer 15

The rapid metabolism of glucose

Question 16

What does the branched structure of glycogen mean?

Answer 16

It means that more enzymes can be used at any one time which produces more glucose molecules at any one time

Question 17

What can’t the phosphorylase enzyme break?

Answer 17

• Can’t break 1 –> 6 bonds (can only break that 1–>4 linkages)
• Can’t breal the 1–> 4 bonds within 4 units of a branching point

Therefore, can only break outer side chains due to limitations as can’t get to the rest of the molecule

Question 18

Branced –> Linear structure using the branching enzyme

Answer 18

Question 19

What happens to muscle glycogen and liver glycogen?

Answer 19

Question 20

What enzyme turns G-1-P to G-6-P?

Answer 20

Question 21

How does the enzyme convert G-1-P to G-6-P?

Answer 21

Question 22

What are the steps to Glucogenesis?

Answer 22

Question 23

Show the steps to glucose metabolism?

Answer 23

Question 24

What two things determine the direction of the glycogenesis reaction?

Answer 24

• speed
• number of possible reactions

Question 25

A disease called McArdle’s means that the mechanism of glycogenesis can’t be reversed, why is this?

Answer 25

Question 26

McArdle’s disease can’t do the first step of glycogenesis so what is the reaction instead that occurs?

Answer 26

Question 27

What are the 4 different things ATP can be used to make?

Answer 27

Question 28

Whats the reaction for G-1-P to UDP-glucose?

Answer 28

Question 29

Whats the role of glycogen synthase in glycogenesis?

What issues does it face?

Answer 29

Question 30

Due to the problems that glycogen synthases faces, what other enzymes are involved and their role to helping form glycogen?

Answer 30

Question 31

Define the following…

1. Glycolysis
2. Glycogenolysis
3. Glycogenesis

Answer 31

1. Glycolysis: Glycolysis is the process of breaking down glucose
2. Glycogenolysis: Glycogenolysis is the breakdown of glycogen (n) to glucose-1-phosphate and glycogen (n-1)
3. Glycogenesis: the formation of glycogen from sugar.