HANDOUT: GLYCOGENESIS and GLYCOGENOLYSIS

Question 1

This is the storage form of glucose

Answer 1

Glycogen

Question 2

How many anomeric carbons does glycogen have?

Answer 2

1 only, although highly branched

This is not linked to another glucose residue

Question 3

What links the glucosyl of glycogens?

Answer 3

a-1,4-glycosidic bonds with a-1,6-branches every 8-10n residues

Question 4

The anomeric carbon is attached to a certain protein at the beginning of the chain. What is this protein? What is the unattached end called?

Answer 4

Glycogenin

Non-reducing end –> unattached end

Question 5

What is the function of the branching structure of the glycogen?

Answer 5

rapid degradation
rapid synthesis of glycogen
[since enzymes can work on different branches at a time]

Question 6

The molecular weight of glycogen polymers present in tissues

Answer 6

107 to 108 Da

Question 7

Where are the regulatory enzymes involved in glycogen synthesis and degradation bound to glycogen particles?

Answer 7

Surface

Question 8

The function of glycogen in most cell types

Answer 8

• reservoir for glucosyl units

Question 9

Muscle glycogen vs Liver glycogen

Answer 9

Muscle glycogen - fuel for ATP production
Liver glycogen - glucose reserve for maintenance of concentration of glucose

Question 10

When is Glycogen an essential fuel source for skeletal muscles?

Answer 10

• High ATP demand
• G6P is being rapidly used in anaerobic glycolysis (During exercise, for example, the glucose is now used rapidly (thus are the G^Ps) in glycolysis, hence why glycogen takes place)

Question 11

Small glycogen reservoir function in other cells

Answer 11

• Emergency fuel source that can be used for ATP generation (when O2 is absent or when blood flow is restricted)

Question 12

The first and immedia†e source of glucose for maintaining blood glucose level

Answer 12

Liver glycogen

Question 13

In the liver, describe what happens to G6P glycogenolysis.

Answer 13

G6P is derived from a degraded glycogen, then glucose-6-phosphatase will hydrolyze gG6P into glucose, which will go into the bloodstream.

Question 14

The enzyme that is only present in the liver and kidney

Answer 14

G-6-phosphatase

Question 15

What does glycogen degradation provide?

Answer 15

• source of blood glucose when dietary glucose decrease
• when there’s an increase in exercise
  when muscles use lots of glucose

Question 16

Describe how glycogen is synthesized

Answer 16

• Glucose enters liver via GLUT2
• Glucose –> G6P (Glucokinase)
• G6P –> G1P
• G1P + UTP —> UDP [active] (pyrophosphatase)
• Glycogenin —> —> Glycogen

Question 17

Describe how glycogen is degraded

Answer 17

• glycosidic bonds between glucosyl of glycogen are broken
• phosphate groups are added
• G1P is formed
• UDP is not synthesized

Question 18

This glycosidic bond is required in Glycogen synthesis to link glycosyl residues in long chains

Answer 18

α-1,4-glycosidic bonds

Question 19

This glycosidic bond is required in Glycogen synthesis to link glycosyl in every 8-10 residues

Answer 19

α-1,6-branch

Question 20

Describe the lengthening of the polysaccharide chains of a pre-existing glycogen molecule

Answer 20

• Most glycogen synthesis occurs through the lengthening of the polysaccharide chains of a preexisting glycogen molecule (polymer)
• reducing end attaches to glycogenin

Question 21

How to lengthen glycogen chains?

Answer 21

• glucosyl residues are added from UDP to the non-reducing end
• this is facilitated by glycogen synthase

Question 22

What facilitates the addition of UDP to the non-reducing end

Answer 22

glycogen synthase

Question 23

The anomeric carbon of each glucosyl residue is attached in an _______________.

Answer 23

α-1,4-glycosidic bond

to the hydroxyl on C4 of the terminal glucosyl residue.

Question 24

When the chain reaches ______, the residues are cleaved.

Answer 24

approximately 11 residues

Question 25

When the chain reaches approximately 11 residues in length, a 6- to 8-residue piece is cleaved by ______________.

Answer 25

amylo-4,6-transferase / branching enzyme

Question 26

Where do branching enzymes reattach the residues they cleaved?

Answer 26

to a glucosyl unit by an α-1,6-bond

Question 27

A Branching Enzyme Forms ____________.

Answer 27

α-1,6 Linkages

Question 28

When muscles are at rest, these are used ________.

Answer 28

Fatty acids

Question 29

Main source of energy when we have just eaten

Answer 29

Glucose from diet
Fats

Question 30

Approaching the starvation at 16-18 hrs, what will happen?

Answer 30

Ketone bodies
glucose from gluconeogenesis