MEH: Energy Storage: Glycogen And Fat

Question 1

Describe the major energy stores in a 70kg man.

Answer 1

• Most is found in triacylglyerol (15kg)
• The next highest store is muscle protein (6kg)
• The least is found in liver glycogen and muscle glycogen (0.3 and 0.1 kg respectively)

Question 2

Describe an outline for the reactions involved in glycogen synthesis.

Answer 2

• Glucose is converted to glucose-6-phosphate through the same process of glycolysis
• Phosphoglucomutase then coverts glucose-6-phosphate to glucose-1-phosphate
• This is converted to UDP-Glucose action of uridylyltransferase (UTP->PPi)
• This is then converted into glycogen using glycogen she and branching enzymes

Question 3

Describe an outline for the reactions involved in glycogen degradation.

Answer 3

• Glycogen is converted into glucose-1-phosphate via glycogen phosphorylase and Debra Ching enzyme
• This is converted into glucose-6-phosphate via phosphoglucomutase
• Glucose-6-phosphate can either be used by the liver and muscle and entered straight into glycolysis
• OR converted into glucose (in the liver only)

Question 4

What is the difference between liver and muscle glycogen?

Answer 4

Glycogen in the muscle is used by the muscle for energy production, whereas In the liver the glucose released is transported in the blood for use by other tissues.

Question 5

Name 2 glycogen storage diseases.

Answer 5

1. Von Glerke’s disease

2. McArdle disease

Question 6

Describe the clinical implications of Von Glerke’s disease.

Answer 6

Glucose-6-phosphate deficiency which results in the enlargement of the liver.

Question 7

Describe the clinical implications of McArdle disease.

Answer 7

Muscle glycogen phosphorylase deficiency

Question 8

How is glucose produced from non carbohydrate sources?

Answer 8

• Lactate from anaerobic glycolysis in exercising muscle and red blood cells
• Glycerol released from adipose tissue breakdown of triglycerides
• Amino acids (mainly alanine)

Question 9

Why is glucose produced from non-carbohydrate sources?

Answer 9

Beyond 8 hours of fasting, liver glycogen stores start to deplete and an alternative source of glucose is required. (Gluconeogenesis).

Question 10

Explain why triacylglyerols can be used as efficient energy storage molecules in adipose tissue.

Answer 10

TAGs are hydrophobic and therefore are stored in an anhydrous form. This means they have no osmotic effect on the cell.

Question 11

Describe how dietary triacylglycerols are processed for storage.

Answer 11

• Fat (TAG) enters the small intestine and is broken down into fatty acids and glycerol by the action of pancreatic lipase
• Intestinal epithelial cells take up these products and reform TAG which is transported in the lymph via chylomicrons
• This travels through the thoracic duct where the lymphatic System drains into the circulatory system at the left subclavian vein
• This TAG now present in the blood can be but into storage when insulin levels are high

Question 12

Describe how fatty acid degradation differs from fatty acid synthesis.

Answer 12

Degradation: Removes 2C as actyl~CoA, occurs in mitochondria, produces NADH and FAD2H, requires small amount of energy to activate fatty acid, insulin inhibits

Synthesis: adds 2C onto malonyl CoA, occurs in cytoplasm, requires NADPH, requires large amounts of energy to drive the process, Insulin stimulates