Glycogen metabolism

Question 1

Glucogenin

Answer 1

• It acts as a primer, by polymerizing the first few glucose molecules, after which other enzymes take over
• 37kDa
• autocatalytic activity for glycosylation
• 5exons, 0,3% protein
• content determines the cellular glycogen content
• glucose on reducing end is attached to glycogenin

Question 2

Location

Answer 2

• liver: maintain blood glucose during fasting and exercise

- muscle: generate ATP for muscle contraction

Question 3

Glucose-6P -> Glucose 1P

Answer 3

• ezyme: PHOSPHOGLUCOMUTASE

- reversible

Question 4

Glucose 1P + UTP -> UDP-glucose

Answer 4

• enzyme: UDP-GLUCOSE PYROPHOSPHORYLASE

- Irreversible

Question 5

UDP-glucose -> Glycogen

Answer 5

• glucose residues tranfered to non-reducing end
• UDP released and reconverted to UTP
• enzyme: GLYCOGEN SYNTHASE (phosphorylated by PKA-> less active)

Question 6

Glycogen -> Glucose 1P

Answer 6

• enzyme: GLYCOGEN PHOSPHORYLASE

- cofactor needed: pyridoxal phosphate

Question 7

Glucose 6P -> Glucose

Answer 7

-enzyme: GLUCOSE 6 PHOSPHATASE

Question 8

Debranching enzymes

Answer 8

1. Transferases: tranfer 3 last units to NR end

2. Hydrolase: hydrolyses the last glucose off

Question 9

Regulation of glycogen metabolism

Answer 9

Allosteric: activated by: high glucose 6P

Covalent:
insulin- synthesis
glucagon & epinephrine - breakdown
AMP and Ca2+- breakdown in muscle