Lecture 7: Glycogen Metabolism

Question 1

what are the steps in glycogen breakdown

Answer 1

1) glycogen
2) glucose-1-phosphate
3) glucose-6-phosphate
- in muscles, G-6-P used in glycolysis
- in liver, dephosphorylated by glucose-6-phosphatase to produce free glucose

Question 2

which enzyme breaks the alpha-1,4 bonds in glycogen and what type of reaction is it

Answer 2

• glycogen phosphorylase

- via phosphorolysis

Question 3

which enzyme breaks the alpha-1,6 bonds in glycogen and what type of reaction is this

Answer 3

• debranching enzyme
• with transferase activity and alpha-1,6 glucosidase activity
• hydrolysis reaction

Question 4

which enzyme catalyses adding of glucose units to glycogen and how does it do this

Answer 4

• glycogen synthase
• adds glucose units in alpha-1,4 linkage
• using UDP-glucose

Question 5

which enzymes are involved in glycogenesis

Answer 5

• glycogen synthase adds glucose units to a chain of more than 4 glucosyl residues. makes alpha 1,4 linkages
• glycogenin carries out the priming function by attaching the first glucosyl residue to its tyrosine
• branching enzyme transfers block of 7 residues to create a new branch with alpha 1,6 linkage

Question 6

which molecules do allosteric regulation of glycogen phosphorylase

Answer 6

• AMP
• ATP
• glucose-6-phosphate

Question 7

which molecules do allosteric regulation of glycogen synthase

Answer 7

glucose-6-phosphate

Question 8

what is phosphorylation catalysed by

Answer 8

protein kinases

Question 9

what is dephosphorylation catalysed by

Answer 9

protein phosphatases