Exam 4 - Glycogen Metabolism

Question 1

The liver consumes glycogen to form []

Muscles consume glycogen to use [] []

Answer 1

• Glucose
• Right away

Question 2

What type of linkage creates the linear portion of glycogen?

What type of linkage creates branch points in glycogen?

Answer 2

1. alpha-1,4 glycosidic linkage
2. Alpha-1,6 glycosidic linkage

Question 3

Branching normally occurs at every [] glycosyl residue within the linear molecule…

Answer 3

fourth

Question 4

Where are the two major sites of glycogen metabolism?

Answer 4

• Liver
• Muscle Cells

Question 5

Glycogenolysis is….?

Answer 5

the breakdown of glycogen into glucose or glucose 6-phosphate

Question 6

Glycogenesis is…

Answer 6

the synthesis of glycogen from glucose

Question 7

If you create glucose from glycogen - what is the net formation of ATP?

Again - what is the net formation of ATP from normal glycolysis

Answer 7

1. NET of 3 ATP since you only need to invest 1 ATP
2. Normal glycolysis NETS you 2 ATP.

Question 8

What are the 2 enzymes used in the formation of glycogen –> Glucose?

Answer 8

1. Glycogen phosphorylase
2. Phoshpglucomutase

Question 9

What does glycogen phosphorylase catalyze?

Answer 9

• Glycogen –> Glucose 1-phosphate
• P_i is used to cleave the alpha-1,4 glycosidic linkage through phosphorolysis yielding glucose 1-phosphate

Question 10

What does phosphoglucomutase catalyze?

Answer 10

• Glucose 1-phosphate —> Glucose 6-phosphat
• interconverst glucose 1-P and glucose 6-P

Question 11

Phosphoglucomutase functions in both glycogen [] and []…..and requires the catalytic intermediate - []

Answer 11

1. Synthesis
2. degradation
3. Glucose 1,6-bisphosphate

Question 12

What enzyme “debranches” glycogen and what is its function?

Answer 12

• “technically” its a 2-step enzymatic process
• 4-alpha-d-gluconotransferase
  
  • removes 3 gluco residues from the linear portion
• amylo-alpha-1,6-glucosidase
  
  • Makes non-phosphorylated glucose

Question 13

What is the first step of Glycogen anabolism?

Answer 13

• Making glucose 6-phosphate from glucose
  
  • hexokinase

Question 14

What enzyme interconverts G-6-P and G-1-P for glycogen anabolism?

Answer 14

• Phosphoglucomutase

Question 15

What enzyme uses glucose 1-phosphate and UTP to form UDP-glucose and PP_i?

Answer 15

Glucose 1-phosphate uridylyltransferase

Question 16

What is the building block for glycogen production?

Answer 16

UDP-glucose

Question 17

What does Glucose 1-phosphate uridylyltransferase add to G-1-P to form the product = UDP-glucose??

Answer 17

• It actually adds a Uridine MONOPhospate
• There is already a phosphate on the glucose so it only had to add one to get the UDP…

Question 18

What enzyme catalyzes the addition of a glucose from UDP-glucose to a glycogen molecule?

Can this enzyme function to create a new storage site for glycogen?

Answer 18

• Glycogen synthase
• NO
  
  • this reaction cannot produce branches and it can only make existing glycogen bigger

Question 19

What enzyme catalyzes the addition of alpha-1,6 linked groups to a linear chain?

How man glucosyl residues does this move to a new branch?

Answer 19

• Branching enzyme
  
  • 1,4-alpha-glucan branching enzyme
• It moves 7 resides to a new branch point

Question 20

What amino acid acts as the starting molecule for glycogen?

Answer 20

Tyrosine

Question 21

How does Tyr become a “primed” starting molecule for glycogen?

What other molecule is required?

Answer 21

1. Glycogenin
2. This is a “self-glcosylating” molecule that adds 8 resudes of UDP-glucose to Tyrosine
3. This forms the primed glycogenin molecule for more linear and branched UDP additions - through their respective means

Question 22

What are the 2 targets for glycogen regulation?

What type of regulation do these experience?

Answer 22

• Glycogen Phosphorylase
• Glycogen Synthase
• Allosteric and Covalent Modification

Question 23

Glycogen Phosphorylase Regulation

1. Phosphorylation by phosphorylase kinase activates the [] []
2. Phosphorylase a is the [] form of the enzyme
3. Phosphorylase b is the [] form of the enzyme
4. Which “enzyme” a or b is phosphorylated?

Answer 23

1. glycogen Phosphorylase
2. active
3. inactive
4. A is phosphorylated

Question 24

Glycogen Phosphorylase Regulation

• What are the 3 effector molecules?
• What will glucagon signal to this enzyme (generically)
• What will insulin signal to this enzyme (generically)

Answer 24

• AMP (+) Phosphorylase b
• Glucose and ATP (-) on phosphorylase a
• Glucagon signals low blood sugar - causes glycogen phosphorylase to be more active and create glucose from glycogen
• Insulin will signal high blood sugar - it will work to repress glycogen phosphorylase activity

Question 25

Glycogen Phosphorylase Regulation * How does Calcium regulate glycogen phosphorylase?

Answer 25

* Technically it doesn't regulate it directly. * However, it regulates the phosphorylase kinase a and b.....and this enzyme phosphorylates the glycogen phosphorylase * Calcium **positively** effects phosphorylase kinase a AND b

Question 26

Glycogen Synthase Regulation 1. When Phosphorylated this enzyme is [] 2. Is this the same or opposite of the regulation for Glycogen phosphorylase?

Answer 26

1. inactive 2. This is opposite 1. when phosphorylated, glycogen phosphorylase is active.

Question 27

Glucose 6-P is a [] effector on Glycogen Synthase b?

Answer 27

* Psyche * Glucose 6-P does not effect glycogen synthase b * **It is a positive effector on glycogen synthase a!**

Question 28

What subunits does glycogen's phosphoprotein phosphatase need to make it an active phosphatase?

Answer 28

* Regulatory protiein - G * Catalytic subunit - C

Question 29

How does the catalytic subunit of the phosphatase become inactve?

Answer 29

1. the catalytic subunit will be completely inactived by phosphorylation of the regulatory subunit 1. this is done by protein kinase A 2. Once inactive, the C subunit will then bind with an inhibitor protein - making it completely inactive.

Question 30

High levels of [] interact with the glycogen synthase to keep it in the inactive form b... How does this mechanism work?

Answer 30

* Glycogen * We dont know!