Glycogen Metabolism

Question 1

in what form is glucose stored in human body

Answer 1

glycogen

Question 2

Where in the body does glycogen synthesis and breakdown occur?

Answer 2

liver and skeletal muscle

Question 3

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

Answer 3

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

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

Question 4

Where in the cell does glycogen synthesis occur?

Answer 4

Cytosol

Question 5

What molecules provide the energy for glycogen synthesis

Answer 5

ATP

UTP

Question 6

1st step in synthesis of glycogen from glucose?

Answer 6

glucose 6P –> glucose 1P

Question 7

enzyme that catalyzes 1st rxn?

Answer 7

phosphoglucomutase

Question 8

UDP glucose pyprophosphorylase catalyzes

Answer 8

Glucose + UDP –> UDP-glucose

Question 9

What protein serves as primer for glycogen synthesis?

Answer 9

glycogenin

Question 10

What reaction does glycogen initiator synthase catalyze?

Answer 10

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

Question 11

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

Answer 11

Glycogen Synthase

Question 12

can glycogen synthase initiate glycogen synthesis de novo?

Answer 12

no, it can only elongate an existing glycogen chain

Question 13

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

Answer 13

to the non reducing end

Question 14

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

Answer 14

Linear

Question 15

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

Answer 15

1,4-alpha-glucan branching enzyme

Question 16

How does branching enzyme work?

Answer 16

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

Question 17

What is the purpose of branching glycogen molecules?

Answer 17

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

Question 18

When is glycogen used as fuel

Answer 18

during strenuous exercise in muscle, fasted state in liver

Question 19

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

Answer 19

no

Question 20

What enzyme is used to break down glycogen

Answer 20

Glycogen Phosphorylase

Question 21

Where does the glycogen phosphorylase cleave the glycogen molecule?

Answer 21

at the alpha 1,4 glycosidic bond

Question 22

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

Answer 22

discontinues cleavage when there are 4 glucose residues remaining on chain

Question 23

What enzyme removes glycogen branches?

Answer 23

debranching enzyme

Question 24

What are the 2 components of debranching enzyme complex?

Answer 24

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

Question 25

glycogenolysis liberates what glucose based molecule?

Answer 25

glucose 1 phosphate

Question 26

what enzyme converts glucose 1P to glucose 6P?

Answer 26

phosphoglucomutase

Question 27

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

Answer 27

Glucose 6-Pase

Question 28

What 2 mechanisms regulate glycogen synthase and glycogen phosphorylase?

Answer 28

allosteric regulation

hormonal regulation

Question 29

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

Answer 29

nonphosphorylated

make glycogen

Question 30

Which form of glycogen phosphorylase is the active form?

Answer 30

phosphorylated

break glycogen

Question 31

What hormone stimulates glycogen breakdown?

Answer 31

glucagon

Question 32

what hormone stimulates glycogen formation?

Answer 32

insulin