glycogen metabolism

Question 1

What is a glycosidic bond?

Answer 1

2 sugar units joined together with an oxygen

Question 2

What is the glycogen structure

Answer 2

Helical structure
up to 120,000 glucose per glycogen molecule
10-40nm diameter

Question 3

what is glycogenolysis

Answer 3

Breaking of glycogen molecules

Question 4

what do phosphorylases do?

Answer 4

Make or break bonds using Pi

Question 5

Why use phosphorolysis in glycogenlysis?

Answer 5

To avoid using ATP (Glyocogen - glucose-6-phosphate requires ATP)

Question 6

Phosphorylase is processive. What does this mean?

Answer 6

Doesn’t let go of its substrate
Second reaction happens quickly because enzyme hasn’t let go of the molecule

Question 7

What do debranching enzymes do?

Answer 7

Transfers glycosyl units to the core chain (to be available for phosphorylation

transferase

Question 8

What does a-1,6-Glucosidase do?

Answer 8

Breaks bonds between glucose units

Hydrolysis

Question 9

What is Glucose 6-phosphatase?

Answer 9

An enzyme complex on the endoplasmic reticulum

Makes free glucose that can be released into the blood

Question 10

Why can’t the glycogen to Glucose-1-P to Glucose 6-P reaction reverse in the body?

Answer 10

The concentrations of molecules decide which direction a reaction goes in in any enzyme reaction.

The concentration of phosphate in the cell is so much higher than the concentration of glucose-1-phosphate so the reaction will always go in this direction (Pi to G-1-P).

There’s little G-1-P around because most is being turned straight into G-6-P. But there’s lots of phosphate around because every time an ATP is broken down it releases Pi

Question 11

How is Glycogen made?

Answer 11

The G-1-P to G-6-P is reversed to make G-1-P

2. G-1-P reacted with UTP to make UDP-glucose. This releases PPi which is then broken down to 2 free Pi’s. The UDP is attached to the glucose
3. UDP-Glucose attaches to Glycogen VIA the glycogen synthase enzyme (therefore needs an existing chain to add onto)

Question 12

Problems with Glycogen synthase

Answer 12

Can’t start a new chain

Can’t introduce branches

All it can do is take an existing chain and make it longer.

This means that additional helper enzymes are needed to completely fabricate glycogen

Question 13

What is glycogenin

Answer 13

Builds initial 8 unit primer chain. Can start with one glucose and grow a chain

After this, Glycogen synthase extends the chain.