Energy Storage

Question 0

Describe the mechanism of glycogenolysis.

Answer 0

Glycogen (n) + Pi —————> Glucose-1-P + Glycogen (n-1)

a-1,4-bonds hydrolysed by glycogen phosphorylase
a-1,6-bonds hydrolysed by de-branching enzyme

Glucose-1-P converted to Glucose-6-P by phosphoglucomutase.

Question 1

Describe the mechanism of glycogen synthesis (glycogenesis)

Answer 1

Glycogen (n) + UDP-glucose ——-> Glycogen (n+1) + UDP

a-1,4-bonds catalysed by glycogen synthase
a-1,6-bonds catalysed by branching enzymes

Glycogen stored in liver and skeletal muscle.

Question 2

How does glycogenolysis differ in the muscle and the liver?

Answer 2

Glycogen ——–> Glucose-1-P ———-> Glucose-6-P

Muscle:
Glucose-6-P ——-> GLYCOLYSIS

Liver:
Glucose-6-P ——–> Glucose ———–> BLOOD
(glucose-6-phospahatase)

Question 3

How is glycogen metabolism regulated?

Answer 3

Glucagon/adrenaline (fasting hormone) activates phosphorylating enzymes (glycogenolysis)

Insulin (storage hormone) inhibits phosphorylating enzymes (glycogenesis)

Question 4

Explain the glycogen storage diseases and what effects they cause.

Answer 4

Excess glycogen storage ——-> tissue damage

Diminished glycogen storage ——–> hypoglycaemia, poor exercise tolerance

e.g. von Gierke’s disease = deficiency of glucose-6-phosphatase

Question 5

What substrates can be used for gluconeogensis?

Answer 5

Lactate 
Galactose 
Fructose 
Glycerol 
Glucogenic amino acids

Question 6

What enzymes are important for gluconeogenesis? How are they regulated?

Answer 6

Fructose-1,6-bisphosphatase

PEPCK catalyses conversion of oxaloacetate to phosphoeneolpyruvate.

Glucagon & cortisol stimulates, and insulin inhibits