Biochemistry Exam 2 Chapter 16

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What is the storage form of glucose? What is the main form it is stored as?

Glycogen (branched polymer)
Why is it optimal for glycogen to be a highly branched polymer?

Permits rapid glucose mobilization and simultaneous release of glucose.

It is not as dense compared to if it was linear. If it was linear it would be tightly packed and harder to mobilize.
At what end are glucose units removed in glycogen?

Non-reducing end
What is the series of conversions of glycogen for glucose mobilization?
- 1) glycogen
- 2) glucose-1-phosphate (G1P)
- 3) glucose-6-phosphate (G6P)
- 4) glucose
Glycogen Phosphorylase (Step 1 in Glycogen Metabolism)
- Glucose Mobilization:
- catalyzes bond cleavage of glycogen by adding a phosphate group (rate controlling step)
Glycogen (n residues) + Pi

Glycogen (n-1 residues) + G1P
Phosphoglucomutase (Step 2 in Glycogen Metabolism)

What is a benefit to this step?
- Glucose Mobilization:
- converts G1P to G6P (since glucose is already phosphorylated, there is no need for the ATP consuming hexokinase process to make G6P from glucose)
G1P + Pi

G1,6P

G6P + Pi
When glucose is mobilized, the liver is unique in it's ability to make G6P available to other tissues. How is this made possible?

G6P gets translocated to the endoplasmic reticulum (where G6Pase is located) then it is hydrolyzed by G6Pase to make glucose.

Glucose then leaves the liver via transport proteins.

G6P + H2O

Glucose + Pi
What are the general steps to glycogen synthesis?
- 1) glucose-6-phosphate (G6P)
- 2) glucose-1-phosphate (G1P)
- 3) UDP-glucose
- 4) glycogen
What is the purpose of UDP-Glucose Phosphorylase in glycogen synthesis?

Why is UDP glucose an activated molecule?

Activates the glucose molecule by adding UTP to G1P producing UDGP. This gets added to glycogen chain.

Converting G1P to glucose has a positive G, making it unfavorable. Pairing G1P with UTP makes the entire reaction exergonic. The hydrolysis of of PPi can be used to drive the reaction to completion making the reaction irreversible.
What is the role of glycogen synthase in glycogen synthesis?

UDPG is transferred to C4-OH group on one of glucose non-reducing ends.
What is the primer that preps glycogen for addition of glycogen residue?

Glycogenin
For glycogen phophorylase to catalyze bond cleavage through addition of a phosphate, how many glucose units must it be away from the branching point?

5 units away
Debranching Enzyme

Removes branches making additional glucose residues accessible for glycogen phosphorylase. It is slower than glycogen phosphorylase.
Branching Enzyme

Responsible for creating more branches on the glycogen by transferring a 7 residue segment from the end of the chain to a glycogen residue
Draw mechanism for Phosphorylase
How is muscle glycogen phosphorylase under allosteric control?
- Low Energy Environment
- Inhibited by ATP and G6P
Activated by AMP
How is glycogen synthase under allosteric control?
- High Energy Environment
- Activated by ATP and G6P
Inactivated by AMP
How is phosphorylase regulated via phophorylation? (Muscle vs. Liver)
- Muscle
- Phosphorylated:
- T State: somewhat active
- R State: completely active
- Un-phosphorylated:
- T State: inactive
- R State: somewhat active
- (Promoted by AMP)
- Liver
- Completely active in R state
How does phosphorylation affect Glycogen Synthase?
- Phosphorylated: less active
- Un-phosphorylated: more active
(Opposite of glycogen phosphorylase)
How is Phosphorylase Kinase affected by phosphorylation? What causes phosphorylation / dephosphorylation?
- Phosphorylated: more active
- (Occurs in alpha and beta subunit by Protein Kinase A)
- Un-phosphorylated: less active
- (Dephosphorylation by PP1)

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Biochemistry Exam 2 Chapter 16

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Biochemistry Exam 2 Questions Chapter 16

Updated

2017-03-08T06:25:23Z

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