Glycogen metabolism

Question 1

Four functions of carbs

Answer 1

• Structural components
• Components of coenzymes
• Required for DNA replication
• Storage of energy

Question 2

Where is glycogen mainly stored?

Answer 2

Liver and skeletal muscle

Question 3

Hows glycogen a-1,4 bonds broken

Answer 3

• By glycogen phosphorylase forms phosphorolysis reaction
• Forms glucose-1-phosphate and glycogen (n-1)

Question 4

Hows glycogen a-1,6 bonds broken, name enzymes involved

Answer 4

• Requires transferase - glucanotransferase
• And debranching enzyme - a1-6 gluosidase
• This leads to a single glucose molecule

Question 5

How is glucose converted to glycogen

Answer 5

Question 6

Describe how glucagon stimulates glycogen breakdown in the liver

Answer 6

Question 7

Glycogen breakdown is stimulated by..

Answer 7

Adrenaline, AMP, Ca2+

Question 8

Whats the role of phosphofructokinase in glyolysis

Answer 8

• Converts fructose-6-phosphate to fructose-1,6-biphosphate

Question 9

What modulates phosphofructokinase

Answer 9

• AMPand fructose-2,6-bisphosphate
• Activity is inhibited by ATP
• Binding of ATP to an allosteric site lowers the affinity of
  enzyme for fructose-6-phosphate
  Regulation of Phosphofructokinase
• AMP competes with ATP and reverses inhibition
• Ratio of ATP:AMP vital in controlling activity
• H+ also inhibits enzymatic activity
• Prevents excessive lactate (lactic acid) production
  and subsequent lowering of blood pH (acidosis)

Question 10

Role of hexokinase

Answer 10

• Converts glucose to glucose 6 phosphate

Question 11

How is hexokinase modulated

Answer 11

• Hexokinase I, II and III (low KM) are inhibited by glucose-6-phosphate (feedback inhibition)
• If phosphofructokinase is inhibited glucose-6 phosphate levels will rise this will feedback into the pathway
• Thereby preventing unnecessary conversion of glucose to glucose-6-phosphate