Glycogen Synthesis Test II

Question 1

Three key steps of Glycogenesis?

Answer 1

1. Trapping and activation of Glucose by Hexo/Glucokinase which catalyzes to G6P.
2. Elongation of Glycogen with Glycogen Synthase
3. Branching with Glucosyl transferase

Question 2

When is glycogenesis favored?

Answer 2

Favored in the fed state with an increase in Blood glucose levels, increased insulin, increased ATP

Question 3

In glycogenesis what form is glycogen synthase and glycogen phosphorylase in?

Answer 3

Synthase is dephosphorylated and active

GP is dephosphorylated and inactive

Question 4

What type of bond links glucose molecules linearly?

Answer 4

a-1,4-glycosidic linkages

Question 5

What type of bond creates branches in glycogenesis?

Answer 5

a-1,6-glycosidic linkages

Question 6

How does glucose get to the UDP- Glucose stage in glycogenesis?

Answer 6

Glucose is phosphorylated by hexokinase/gluco into G6P.

G6P is reversibly isomerized to Glucose-1-p by Phosphoglucomutase (PGM)

G1P is transfered to UTP by Uridine diphosphage-glucose pyrophosphorylase which generates UDP Glucose

Question 7

What two substrates make UDP-Glucose?

Answer 7

G1P + UTP

Question 8

How does elongation of a glycogen primer occur?

Answer 8

Glycogen synthase the rate limiting enzyme catalyzes transfer of glucose from UDP-Glucose to non reducing end of glycogen chain.

Question 9

How does branching of glycogen chains occur?

Answer 9

When the chain reaches about 11 long 7 residues are broken off at the a-1,4 link and re attached by an a-1,6 link by Glucosyl(4:6) transferase

Question 10

What is the rate limiting enzyme of glycogenesis?

Answer 10

Glycogen Synthase

Question 11

What does branching do to the glycogen?

Answer 11

Increases its solubility and increases the rate it can be made and broke down

Question 12

Describe steps of glycogenolysis.

Answer 12

Glycogen –>G1P –> G6P–> can go to Glycolysis, broke further into glucose by liver, or into the Pentose phosphate pathway

Question 13

What stimulates Glycogenolysis?

Answer 13

Low blood glucose levels, high glucagon

Question 14

What is the RLS of glycogenolysis?

Answer 14

Glycogen being broke to Glucose-1-phosphate by glycogen phosphorylase

Question 15

What occurs during glycogenolysis?

Answer 15

Glycogen broke to G1P by Glycogen Phosphorylase

G1P converted to G6P using phosphoglucomutase

Question 16

How does the phosphoglucomutase enzyme work? Glycogenolysis

Answer 16

A phosphoryl group is transferred from the enzyme to substrate at position 6, there is already one at position 1. Next the phosphate at position one is removed and G6P is left.

Question 17

How does the branch transfer and release of glucose occur? Glycogenolysis

Answer 17

Transferase moves 3 of the four remaining glucose to the non reducing end of chain forming a14 bond. Then Debranching enzyme (a-1,6-glucosidase) cleaves the a16 bond to release the remaining glucose. Glucose is then phosphorylated by hexokinase.

Question 18

What is G6P’s fate in the liver and muscle in glycogenolysis?

Answer 18

Muscle cells don’t have glucose-6-phosphatase so G6P cannot leave the cell. Liver does have this enzyme though, so it converts G6P to glucose for release into the blood stream.

Question 19

If acid maltase, found in lysosomal glycogenolysis, is defective what disease results?

Answer 19

Pompe disease (GSDII)
Can give IV of recombinant human a-glucosidase

Question 20

If there is a deficiency in a-1,6-glucosidase (debranching) enzyme what occurs and what disease?

Answer 20

GSD III/Cori

Glycogen molecules with large number of short branches

Question 21

Deficiency in glucosyl (4:6) transferase (branching) what disease results?

Answer 21

Anderson Disease/ GSD IV

long chain glycogen few branches death by 5, cirrhosis

Question 22

Deficiency in muscle glycogen phosphorylase?

Answer 22

GSD V/ McArdle Disease
Rate limiting step of glycogen breakdown, un able to supply muscles with enough glucose, muscle cramps weakness, myoglobinuria

Question 23

Deficiency in liver glycogen phosphorylase?

Answer 23

GSD VI/Hers Disease

Prevents glycogen breakdown in liver-hepatomegaly and low blood glucose levels