Module 10: Carbohydrate Metabolism - Glycogen Metabolism (Part 03)

Question 1

This process is known as the biosynthesis of glycogen.

Answer 1

Glycogenesis

Question 2

This process is known as the breakdown of glycogen to glucose 1 phosphate.

Answer 2

Glycogenolysis

Question 3

This phenomenon is anaerobically generated, which uses glycogen as a rapid energy source.

Answer 3

Glycogenolysis

Question 4

In Glycogenolysis, how many atp is generated per glucose.

Answer 4

3 ATP

Question 5

In Glycogenolysis, how many atp is generated per non-glycogen glucose?

Answer 5

2 ATP

Question 6

What are the disadvantages of glycogenolysis?

Answer 6

(1) Low ATP/Mass
(2) Limited Storage

Question 7

This provides a rapid source of energy.

Answer 7

Muscle

Question 8

This provides maintains blood glucose levels.

Answer 8

Liver

Question 9

This provides the storage form of glucose that can be used by the cell if glucose is low or deficient. A branched polymer of α-D-glucose linked by a-1,4 glycosidic linkage

Answer 9

Glycogen

Question 10

What linkage does glycogen have?

Answer 10

α-D-glucose linked by a-1,4 glycosidic linkage

Question 11

where does glycogen arise?

Answer 11

Branches arise from frequent a-1,6 glycosidic linkages (every 4th glucosyl residue). Occurs in all tissues but predominantly in liver and muscles

Question 12

This is the largest capacity to store glycogen. This stores and exports glucose to maintain blood glucose between meals via the enzyme glucose-6-phosphatase which converts glucose-6-phosphate to glucose

Answer 12

Liver

Question 13

The liver stores and exports glucose to maintain blood glucose between meals via the enzyme __________________-which converts glucose-6-phosphate to glucose

Answer 13

glucose-6-phosphatase

Question 14

Glycogen store is almost depleted after ______________of fasting

Answer 14

12-18 hours

Question 15

Glycogen is _______of the liver weight (well fed)

Answer 15

10%

Question 16

This has greater total glycogen concentration due to greater mass than liver. It provides a readily available source of glucose for glycolysis (fuel reserve)

Answer 16

Muscle

Question 17

About _______________of total body glycogen is in the muscle

Answer 17

three quarters

Question 18

This mobilizes muscle glycogen thereby releasing ATP.

Answer 18

Exercise

Question 19

Why doesn’t muscle directly yield free glucose?

Answer 19

Does not directly yield free glucose due to absence of glucose-6-phosphatase

Question 20

Glycogen is _______of the muscle weight (well fed)

Answer 20

2 %

Question 21

Why do we store glycogen rather than glucose?

Answer 21

(1) Glucose is osmotically active
(2) Glycogen is more inert (can be stored)
(3) Highly soluble which is a ready source of fuel
(4) Easier to be released than fat
(5) Can be metabolized even in anaerobic conditions

Question 22

What happens in step 1 in glycogen synthesis?

Answer 22

Glucose priming through phosphorylation

Question 23

What enzymes facilitate glucose priming through phosphorylation?

Answer 23

(1) Glucokinase (hexokinase IV in the liver
(2) Hexokinase (Hexokinase I and II in the muscle)

Question 24

what enzyme is responsible for the formation of glucose 1 phosphate?

Answer 24

phosphoglucomutase (isomerase)

Question 25

What happens in step 3 in glycogen synthesis?

Answer 25

Formation of UDP glucose

Question 26

What happens in step 4 of glycogen synthesis?

Answer 26

Transfer of glucose to a non reducing glycogen

Question 27

What enzyme facilitates the Transfer of glucose to a non reducing glycogen ?

Answer 27

Glycogen synthase (where the free energy of glucose 1 phosphate is highly favorable)

Question 28

What happens in step 5 of glycogen synthesis?

Answer 28

Branch formation where 6 to 7 from the 11 residues built is transferred to a branch. if the branching solubility increases, the non reducing ends also increase.

Question 29

What enzyme is responsible for the glycogen branching?

Answer 29

Glycogen branching enzyme or amylo transglycolase

Question 30

What does glycogen synthase require?

Answer 30

Requires a primer - glycogenin

Question 31

This catalyzes two distinct reactions. Initial attack by the hydroxyl group of Tyr194 on C-1 of the glucose moiety of UDP-glucose results in a glycosylated Tyr residue.

Answer 31

Glycogenin

Question 32

what happens in glycogen synthesis?

Answer 32

The C-1 of another UDP-glucose molecule is now attacked by the C-4 hydroxyl group of the terminal glucose, and this sequence repeats to form a nascent glycogen molecule of eight glucose residues attached by (a-1→4) glycosidic linkages.

Question 33

This cannot initiate synthesis of a new glycogen chain de novo. It requires a primer, a preformed (a 1 -> 4) polyglucans chain or branch having at least 8 glucose residues

Answer 33

Glycogen synthase

Question 34

This acts both as a primer and a self-glycosylating enzyme by adding glucose to itself from UDP-glucose.

Answer 34

Glycogenin

Question 35

What are the two reactions catalyzed by glycogenin?

Answer 35

(1) Attack by –OH group of tyrosine on C1 of UDP-glucose (2) C1 of another UDP-glucose is now attacked by C-4 OH of terminal glucose residues lengthening the chain by 1 glucose unit. This is repeated until about 8 glucose units are added then glycogen synthase takes over.

Question 36

This adds glucose units from UDP-glucose to a non-reducing end of glycogen

Answer 36

Glycogen Synthase

Question 37

This catalyzes transfer of 6-7 glucose residues to C6 OH of glucose of another chain, creating a new branch.

Answer 37

Glycogen Branching Enzyme

Question 38

What is the biologic effect of branching?

Answer 38

(1) Increase solubility of glycogen (2) Increases the number of non-reducing ends increasing the sites for the action of glycogen phosphorylase and glycogen synthase (3) To make synthesis and breakdown of glycogen occur more rapidly

Question 39

How is the regulation of glycogenesis promoted?

Answer 39

when the blood glucose is high after a meal

Question 40

This enzyme promotes glycogenesis.

Answer 40

Insulin

Question 41

This enzyme subject to regulation. It is active when dephosphorylated but inactive when phosphorylated.

Answer 41

Glycogen Synthase

Question 42

This is known as the breakdown of glycogen to glucose or glucose-1-P

Answer 42

Glycogenolysis

Question 43

Where does glycogenolysis occur?

Answer 43

Occur abundantly in muscle and liver but virtually absent in liver after 24 hours of fasting or heavy exercise

Question 44

This catalyzes phosphorolysis of glycogen, a Pi is used to cleave an α-1,4 glycosidic linkage to form glucose1-Phosphate

Answer 44

Glycogen Phosphorylase

Question 45

Where does Glycogen Phosphorylase occur?

Answer 45

Non reducing ends

Question 46

Glycogen phosphorylase requires this as a cofactor.

Answer 46

pyridoxal phosphate, PLP

Question 47

Liver glycogen can be depleted in __________________.

Answer 47

12 to 24 hrs.

Question 48

What are the three enzymes that facilitates glycogenolysis?

Answer 48

(1) Glycogen phosphorylase - releases glucose 1 phosphate (2) Debranching Enzyme (3) Phosphoglucomutase - converts G1P to G6P

Question 48

What does the action of glycogen phosphorylase do

Answer 48

Prevents cleaved glucose from leaving the cell

Question 49

What are the two (2) debranching enzymes that has catalytic actvities?

Answer 49

(1) Oligo-1,4 to 1,4- glucan transferase (2) Amylo-1,6-glucosidase

Question 49

How many net yield of glucose are there from glycogen?

Answer 49

Note: if glucose comes from glycogen when it enters glycolysis, it is already phosphorylated. Saves one ATP. Net yield of glucose from glycogen is 3 ATPs instead of 2.

Question 50

This enzyme subject to regulation by allosteric effectors that signal the energy status of the cell.

Answer 50

Glycogen phosphorylase

Question 50

Glycogen phosphorylase is active or responsive to hormones like what?

Answer 50

Insulin, Glucagon, Norepinephrine

Question 51

When is glycogen phosphorylase active?

Answer 51

It is active when phosphorylated and inactive when dephosphorylated.

Question 52

These activates glycogen phosphorylase by phosphorylation

Answer 52

Glucagon and epinephrine