Glycogenesis

Question 1

Where is glycogen stored?

Answer 1

Liver- up to 10% of weight

Muscle- 1-2% of weight

**Most glycogen is stored in muscle because there is more muscle in the body

Question 2

Why is glycogen stores limited?

Answer 2

Glycogen is very heavy, 60% water. Once the threshold is met, glucose will be turned into fat.

Question 3

Glycogen and its two forms

Answer 3

Each glycogen can contain 1000-12000 glucose molecules

1. Alpha- 1,4 linkage (Linear)- Formed by glycogen synthase
2. Alpha- 1,6 linkage (Branching)- Formed by branching enzyme (Transglycosylase)

Question 4

What form of glycogen is the most soluble?

Answer 4

alpha-1,6 linkage (branched)

Question 5

glycogen synthase

Answer 5

forms alpha-1,4 linkage

From UDP-glucose –> glycogen

Question 6

Transglycosylase (branching enzyme)

Answer 6

forms alpha-1,6 linkage

Question 7

Steps of Glycogenesis

Answer 7

1. Glucose trapped in liver by glucokinase and in muscle by hexokinase –> glucose-6-phosphate
2. Formation of activated glucose
   glucose-6-phosphate –> glucose-1-phosphate –> UDP-glucose
3. Formation of glycogen
   UDP-glucose –> alpha 1,4 linkage glycogen (by glycogen synthase)

Question 8

phosphoglucomutase

Answer 8

Used for start of formation of activated glucose

glucose-6-phosphate –> glucose-1-phosphate

Question 9

UDP-glucose pyrophosphorylase

Answer 9

last part of formation of activated glucose step

glucose-1-phosphate –> UDP- glucose

Question 10

Glycogen branching formation

Answer 10

Since linear form has low permeability/solubility, when chain reaches 8-14 units of 1,4 glucose, it will reorganize into 1,6 linkage using branching enzyme (Transglycosylase) to increase permeability/solubility

Question 11

How is glycogenesis regulated?

Answer 11

Insulin activates glycogen synthase through protein phosphatase 1 (which responds to increased insulin, and dephosphorylates glycogen synthase resulting in glycogen synthase binding glycogen)