Unit 10

Question 1

Compare and contrast

the principal functions of glycogen in muscle and liver.

Answer 1

most cells do not store much glycogen but both of these do.

liver- glycogen broken down to glucose 1-phosphate, then glucose-6 phosphate then glucose. Used to maintain blood glucose.

Muscles- glycogen broken down to glucose 1-phosphate then glucose 6-phosphate then proceeds through glycolysis.

Question 2

Describe the role of glycogenin in glycogen synthesis

Answer 2

Glycogenin can play an important role in glycogen synthesis if there is no glycogen fragment present, glycogenin serves as acceptor of glucose residues from UDP-glucose.

This reaction is catalysed by glycogenin itself and is called autoglucosylation.

Glycogenin then catalyses the transfer of the next few molecules of glucose from UDP-glucose, this produces a short glucosyl chain.

Question 3

Describe the role of glycogen synthase in glycogen synthesis and its particular requirements.

Answer 3

it elongates glycogen chain

makes the alpha (1->4) linkages in glycogen.

Some of the particular requirements are that there has to be UDP-glucose so that the elongation can happen.

Question 4

How are the α(1—>6) bonds formed in glycogen and what do these bonds
do to the structure of glycogen?

Answer 4

formed due to ‘branching enzyme’ that transfers a chain of six to eight glucosyl residue from the non-reducing end of the glycogen chain

this breaks the α(1—>4) bond to another residue on the chain and attaches it by an α(1—>6) linkage.

Question 5

Describe two biological advantages
of synthesizing glycogen with many
branches.

Answer 5

branching increases solubility and also it allows the rate at which glycogen synthesis and degradation can occur. (page 128)

Question 6

Glycogen synthesis and glycogen breakdown are catalyzed by separateenzymes. What is the advantage of this strategy in terms of regulation and what type of regulation is employed at these steps?Hint: review Table 7 in Unit 6

Answer 6

able to be regulated due to enzyme activity

Having multiple enzymes they are able to each be controlled but a ‘multi-subunit complex’.

Question 7

List the three general steps in the degradation of glycogen

Answer 7

• shortening of chain by glycogen phosphorlylase
• removal of branches due to enzyme activities
• conversion of glucose 1-phosphate to glucose 6-phosphate

Question 8

How does the well fed state affect glycogen storage? Include in your answer the effect of phosphorylation or dephosphoyrlation on
glycogen synthase and glycogen phosphorylase.

Answer 8

it increases the release of insulin and decreases the release of glucagon which leads to protein phosphatase activity

Glycogen synthase is activated by glucose 6-phosphate, however glucose 6-phosphate also inhibits glycogen phosphorylase.

Question 9

How does the fasting state affect glycogen storage? Include in your answer the effect of phosphorylation or dephosphorylation on
both glycogen synthase and glycogen phosphorylase?
.

Answer 9

decreases the release of insulin and increases the release of glucagon.

Question 10

What are glycogen storage diseases and name one example (including its
defect) from glycogen degradation and glycogen synthesis.

Answer 10

caused by the deficiency in phosphate

Von Gierke Disease (inability for liver to provide glucose during fasting state)

affects glycogen degradation and last step of gluconeogenesis