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Biochemistry > Module 10: Carbohydrate Metabolism - Glycogen Metabolism (Part 03) > Flashcards

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

1
Q

This process is known as the biosynthesis of glycogen.

A

Glycogenesis

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2
Q

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

A

Glycogenolysis

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3
Q

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

A

Glycogenolysis

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4
Q

In Glycogenolysis, how many atp is generated per glucose.

A

3 ATP

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5
Q

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

A

2 ATP

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6
Q

What are the disadvantages of glycogenolysis?

A

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

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7
Q

This provides a rapid source of energy.

A

Muscle

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8
Q

This provides maintains blood glucose levels.

A

Liver

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9
Q

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

A

Glycogen

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10
Q

What linkage does glycogen have?

A

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

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11
Q

where does glycogen arise?

A

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

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12
Q

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

A

Liver

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13
Q

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

A

glucose-6-phosphatase

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14
Q

Glycogen store is almost depleted after ______________of fasting

A

12-18 hours

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15
Q

Glycogen is _______of the liver weight (well fed)

A

10%

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16
Q

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

A

Muscle

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17
Q

About _______________of total body glycogen is in the muscle

A

three quarters

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18
Q

This mobilizes muscle glycogen thereby releasing ATP.

A

Exercise

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19
Q

Why doesn’t muscle directly yield free glucose?

A

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

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20
Q

Glycogen is _______of the muscle weight (well fed)

A

2 %

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21
Q

Why do we store glycogen rather than glucose?

A

(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

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22
Q

What happens in step 1 in glycogen synthesis?

A

Glucose priming through phosphorylation

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23
Q

What enzymes facilitate glucose priming through phosphorylation?

A

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

24
Q

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

A

phosphoglucomutase (isomerase)

25
Q

What happens in step 3 in glycogen synthesis?

A

Formation of UDP glucose

26
Q

What happens in step 4 of glycogen synthesis?

A

Transfer of glucose to a non reducing glycogen

27
Q

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

A

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

28
Q

What happens in step 5 of glycogen synthesis?

A

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.

29
Q

What enzyme is responsible for the glycogen branching?

A

Glycogen branching enzyme or amylo transglycolase

30
Q

What does glycogen synthase require?

A

Requires a primer - glycogenin

31
Q

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.

A

Glycogenin

32
Q

what happens in glycogen synthesis?

A

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.

33
Q

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

A

Glycogen synthase

34
Q

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

A

Glycogenin

35
Q

What are the two reactions catalyzed by glycogenin?

A

(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.

36
Q

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

A

Glycogen Synthase

37
Q

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

A

Glycogen Branching Enzyme

38
Q

What is the biologic effect of branching?

A

(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

39
Q

How is the regulation of glycogenesis promoted?

A

when the blood glucose is high after a meal

40
Q

This enzyme promotes glycogenesis.

A

Insulin

41
Q

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

A

Glycogen Synthase

42
Q

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

A

Glycogenolysis

43
Q

Where does glycogenolysis occur?

A

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

44
Q

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

A

Glycogen Phosphorylase

45
Q

Where does Glycogen Phosphorylase occur?

A

Non reducing ends

46
Q

Glycogen phosphorylase requires this as a cofactor.

A

pyridoxal phosphate, PLP

47
Q

Liver glycogen can be depleted in __________________.

A

12 to 24 hrs.

48
Q

What are the three enzymes that facilitates glycogenolysis?

A

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

48
Q

What does the action of glycogen phosphorylase do

A

Prevents cleaved glucose from leaving the cell

49
Q

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

A

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

49
Q

How many net yield of glucose are there from glycogen?

A

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.

50
Q

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

A

Glycogen phosphorylase

50
Q

Glycogen phosphorylase is active or responsive to hormones like what?

A

Insulin, Glucagon, Norepinephrine

51
Q

When is glycogen phosphorylase active?

A

It is active when phosphorylated and inactive when dephosphorylated.

52
Q

These activates glycogen phosphorylase by phosphorylation

A

Glucagon and epinephrine

Biochemistry (16 decks)

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