Glycogen Metabolism

Question 1

Which parts of the body have the most blood glucose demand?

Answer 1

Brain and RBC. They both consume 80% of the 200g of glucose consumed by body per day.

Question 2

Why is it necessary for our body to keep replenishing blood glucose levels?

Answer 2

1. Our blood plasma only has 10g of glucose at once (around 5% of what our body needs)
2. Glucose is absorbed from our intestines only 2-3 hours after a carbohydrate meal.

Question 3

What are the symptoms of hypoglycemia?

Answer 3

1. Compromised brain function (confusion and disorientation)
2. Coma

Hypoglycemia: 2.5 mmol/dL (45 mg/dL)

Question 4

How is glycogen stored in the cytosol?

Answer 4

As granules

Question 5

Why is glycogen preferred over fat for energy breakdown?

Answer 5

1. Muscles cannot mobilise fat as effectively as glycogen.
2. Fatty acids cannot be metabolised under anaerobic conditions (G-6-P can enter glycolysis to give pyruvate, then lactose)
3. Fatty acids cannot be converted back to glucose. (Pyruvate to Acetyl CoA is irreversible)

Question 6

Which organ stores the mst glycogen per tissue mass?

Answer 6

Liver (10g/100g)

Question 7

How much glycogen is stored in muscle and in liver?

Answer 7

Muscle: 300- 400g
Liver: 100g

Question 8

When is muscle and liver glycogen depleted?

Answer 8

Muscle: Muscle contraction
Liver: After 12-18 hours of fasting

Question 9

Where is the glucose added to the glycogen primer?

Answer 9

To the non reducing end by the alpha-1,4 glycosidic bond.

Question 10

What is glycogenin?

Answer 10

Glycogenin is a glycoprotein with two polypepetide chains that acts as the glycogen primer.

Question 11

What is the property of glycogen synthase?

Answer 11

It is a glycosyl transferase

Question 12

What is the property of the branching enzyme?

Answer 12

1. Transglycosylase (alpha 1,6 bond)
2. Glucosidase (alpha 1,4 bond)

Question 13

What are the properties of the debranching enzyme?

Answer 13

Glucosidase (alpha 1,6 bond)

Question 14

Why can’t muscle glycogen regulate blood glucose level?

Answer 14

Blood lacks G-6-P phosphatase, hence it cannot dephosphorylate G-6-P to give free dlucose to release into the blood.

Question 15

Which is the regulatory/ rate limiting step of glycogenesis?

Answer 15

Glycogen synthase

Question 16

What is the regulatory/ rate limiting step for glycogenolysis?

Answer 16

Glycogen phosphorylase

Question 17

How does Glycogen phosphorylase work?

Answer 17

Breaks apha 1,4 bond and stops 3-4 units away from the branching point.

Question 18

What is a coenzyme for Glycogen phosphorylase?

Answer 18

PLP (Pyridoxine 5’ phosphate, derived from vitamin B6)

Question 19

Which are the primary and secondary messenger of glycogenesis and glycogenolysis regulation?

Answer 19

1. Primary: Glucagon and Epinephrine
2. Secondary: cAMP

Question 20

When do epinephrine and glucagon regulate glycogenesis and glycogenolysis?

Answer 20

In the state of starvation or hypoglycemia to sop glycogen synthesis and stimulate its breakdown.

Question 21

What are Glycogen Storage Diseases?

Answer 21

It is a term given to a group of inherited disorders with:
1. Deposition of abnormal type of glycogen
2. Deposition of abnormal quantity of glycogen
3. Failure to mobilise glycogen

Question 22

What is Glycogen Storage Disease Type 1 also called?

Answer 22

von Gierke’s Disease

Question 23

What is the cause of Glycogen storage disease Type 1?

Answer 23

Deficiency in Glucose 6 phosphatase

Question 24

What are the salient features of Glycogen Storage Disease Type 1?

Answer 24

1. Hypoglycemia
2. Hyperlipidemia
3. Lactic Acidosis
4. Ketosis
5. Osteoporosis
6. Hyperuricemia
7. Increased infections and Mouth ulcers
8. Liver enlargement
9. Impaired growth and delayed puberty

Question 25

How is von Gierke's disease diagnosed?

Answer 25

Liver biopsy

Question 26

What are suitable treatment options for von Gierke's disease?

Answer 26

1. Giving food at short intervals 2. Nasogastric feeding at night