Glycogen Metabolism Flashcards Preview

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Flashcards in Glycogen Metabolism Deck (32)
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1
Q

in what form is glucose stored in human body

A

glycogen

2
Q

Where in the body does glycogen synthesis and breakdown occur?

A

liver and skeletal muscle

3
Q

What types of linkages btw glucose molecules may be found in glycogen?

A

alpha-1,4-glycosidic bonds (straight chain linkage)

alpha-1,6-glycosidc bonds (branch points)

4
Q

Where in the cell does glycogen synthesis occur?

A

Cytosol

5
Q

What molecules provide the energy for glycogen synthesis

A

ATP

UTP

6
Q

1st step in synthesis of glycogen from glucose?

A

glucose 6P –> glucose 1P

7
Q

enzyme that catalyzes 1st rxn?

A

phosphoglucomutase

8
Q

UDP glucose pyprophosphorylase catalyzes

A

Glucose + UDP –> UDP-glucose

9
Q

What protein serves as primer for glycogen synthesis?

A

glycogenin

10
Q

What reaction does glycogen initiator synthase catalyze?

A

UDP-glucose + glycogenin + glucose –> UDP + linked glucose molecules

11
Q

enzyme responsible for creating the alpha-1,4 linkage btw glucose molecules?

A

Glycogen Synthase

12
Q

can glycogen synthase initiate glycogen synthesis de novo?

A

no, it can only elongate an existing glycogen chain

13
Q

where on the newly synthesized glycogen chain are new glucose molecules added?

A

to the non reducing end

14
Q

What would be the shape of a glycogen molecule if glycogen synthase was the only enzyme adding glucose to the the chain?

A

Linear

15
Q

What is the enzyme responsible for creating alpha 1,6 glycosidic bonds between glucose molecules?

A

1,4-alpha-glucan branching enzyme

16
Q

How does branching enzyme work?

A

transfers approximately 5-8 glucose residues from non reducing end of glycogen chain to another residue with the chain and attaches the residues via an alpha 1,6 linkage

17
Q

What is the purpose of branching glycogen molecules?

A

to facilitate buildup of glycogen
increases solubility of glycogen
creates a large number of terminal residues, which are substrates for Glycogen Synthase and Glycogen Phosphorylase

18
Q

When is glycogen used as fuel

A

during strenuous exercise in muscle, fasted state in liver

19
Q

is the process of glycogen breakdown the reverse of glycogen synthesis?

A

no

20
Q

What enzyme is used to break down glycogen

A

Glycogen Phosphorylase

21
Q

Where does the glycogen phosphorylase cleave the glycogen molecule?

A

at the alpha 1,4 glycosidic bond

22
Q

How far away from the reducing end of the glycogen molecule can glycogen phosphorylase cleave?

A

discontinues cleavage when there are 4 glucose residues remaining on chain

23
Q

What enzyme removes glycogen branches?

A

debranching enzyme

24
Q

What are the 2 components of debranching enzyme complex?

A

Transferase which removes the 1st there glucose residues left on a branch of glycogen.

alpha 1,6-glucosidase- removes the last glucose residue on a branch of glycogen

25
Q

glycogenolysis liberates what glucose based molecule?

A

glucose 1 phosphate

26
Q

what enzyme converts glucose 1P to glucose 6P?

A

phosphoglucomutase

27
Q

which enzyme found on the ER of liver cells is responsible for liberating free glucose?

A

Glucose 6-Pase

28
Q

What 2 mechanisms regulate glycogen synthase and glycogen phosphorylase?

A

allosteric regulation

hormonal regulation

29
Q

Which form of glycogen synthase, phosphorylated or nonphosphorylated is the active form?

A

nonphosphorylated

make glycogen

30
Q

Which form of glycogen phosphorylase is the active form?

A

phosphorylated

break glycogen

31
Q

What hormone stimulates glycogen breakdown?

A

glucagon

32
Q

what hormone stimulates glycogen formation?

A

insulin