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Flashcards in Glycogen Metabolism Deck (59):
1

What is the main storage form of glucose?

Glycogen

2

Where are the largest amounts of glycogen found?x

Liver and skeletal muscle

3

Does glycogenesis require energy? Glycogenolysis?

Yes, no

4

What is glycogen made of?

Alpha 1-4 and alpha 1-6 glycosidic linkages

5

Where are branches formed?

At alpha-1,6-bonds

6

What is attached at the reducing end of each glycogen molecule?

Glycogenin

7

Can glycogen be degraded rapidly?

Yes, enzymes are present and can work on several chains simultaneously

8

What is the purpose of liver glycogen? Skeletal muscle glycogen?

Glucose for blood; glucose for ATP use in muscle contraction

9

Does muscle have G6Pase?

No, it doesn’t need it, only uses glucose for ATP, does not have gluconeogenesis

10

What provides energy for glycogenesis?

UTP

11

What is the glucose donor in glycogen synthesis?

UDP-Glucose

12

What enzyme catalyzes synthesis of glycogen in alpha 1,4 linkages? 1,6?

Glycogen synthase, amylo 4-6 transferase

13

What is the regulated step in glycogen degradation?

Glycogen phosporylase

14

What removes 3 glucosyl residues from glycogen (debranching enzyme)

Transferase

15

What hydrolyzes alpha 1,6 glycosidic linkages ?

A-1-6- Glucosidase

16

T or F: Insulin/glucagon ratio is low glycogen is degraded

True

17

When you phosphorylate glycogen phosphorylase is it active? What about glycogen synthase?

Yes, No

18

What removes phosphates from glycogen phosphorylase & glycogen synthase?

Hepatic protein phosphatase 1

19

In fasting is the answer to #423 active?

no (leaves P on glycogen synthase making it inactive and P on glycogen phosphorylase making it active glycogen breakdown and no glycogen synthesis)

20

Does AMP activate liver glycogen phosphorylase?

No, Only in muscle

21

Does glucose inhibit glycogen phosphorylase in muscle?

No, Only in liver

22

Describe GSD Type I along with location

Glucose 6 phosphatase deficiency (Von Gierke’s); hepatomegaly, normal glycogen structure
Location: liver and kidneys

23

Describe GSD Type II along with location

Alpha 1,4 glucosidase deficiency (Pompe’s); cardiomegaly, debranching enzyme deficiency
Location: heart, muscle, liver

24

Describe GSD Type III along with location

Debranching deficiency (Cori’s disease), hepatomegaly, dx. By excessive branched glycogen in urine
Location: liver, skeletal muscle, heart

25

Describe GSD Type IV along with location

Branching deficiency; dx. By glycogen that has no branches in urine
Location: liver, muscle

26

Describe GSD Type V along with location

Muscle phosphorylase deficiency (McArdles); accumulation of glycogen in muscle, reduced ability to degrade muscle glycogen, lactate not produced in exercise, dx. By measuring lactate deficiency

Location: skeletal muscle

27

Describe GSD Type VI along with location

Liver phosphorylase deficiency

28

Describe GSD Type VII along with location

Muscle PFK-1 deficiency (elevated F26BP and G6P)

29

Describe GSD Type IX along with location

Liver phosphorylase kinase defect

30

Describe GSD Type X along with location

PKA, cAMP dependent defect

31

What pathways are affected when glucagon is released? How?

increase in glycogenolysis, gluconeogenesis, lipolysis
Decrease in liver glycolysis

32

What pathways are affected when insulin is released? How?

Increase in glycogen synthesis, FA synthesis, Triglyceride synthesis, liver glycolysis

33

Glycogen is a branched chain homopolymer made up of glucose residues linked where? Where do the branches form?

alpha-1,4- and alpha-1,6-bonds

at the alpha-1,6-bonds

34

Why do branched structures allow rapid degradation and synthesis of glycogen?

enzymes can work on several chains simultaneously and it enhances the solubility of the molecule

35

What produced the branches of glycogen?

the branching enzyme => glucosyl 4,6 transferase

36

What is the precursor for glycogen synthesis? Name its action and place of action on the glycogen

UDP glucose supplies glucose moieties that are added to the nonreducing ends of a glycogen primer by glycogen synthase

37

What does glycogen degradation produce?

glucose 1-phosphate as major product but also free glucose

38

What supplies glucose for ATP generation when demands are high? What stimulates this? Why is this necessary?

skeletal muscle
epinephrine, bc muscle does not have glc-6-P

39

What probides glc-6-P for hydrolysis to maintain blood glucose? What stimulates the breakdown?

liver
glucagon and epinephrine

40

T/F synthetic pathway requires energy from ATP

false, UTP

41

What is the common intermediate for glycogenesis(glycogen synthesis) and glycogenolysis (degradation)?

glucose -1- Phosphate

42

What are the stages of glycogen synthesis?

1. synthesis of UDP glucose
2. action of glycogen synthase
3. formation of branches (4:6 transferase)
4. growth of glycogen chains (UDP glucose/glycogen synthase)

43

When lengthening the polysaccharide chains of a pre-existing glycogen, what is the regulated step?

glycogen synthase adding to the glucosyl residue from UDP-glc to chain

44

Describe the primer used in glycogen synthase activity

glycogenin is the protein which glycogen is attached and has autoglycosylation abilities
1. catalyzes add'n of glucosyl resude from UDG gluc to a tyrosine residue
2. extend the chain until it is long enough to serve as a primer
3. De novo glycogen synthesis for addition of glucosyl residue

45

What are the steps in glycogen degradation?

1. action of glycogen phosphorylase
2. removal of branches (4:4 transferase as debranching enzyme)
3. degradation of glycogen chains
4. fate of glucosyl units released from glycogen

46

What is the regulated step of glycogenolysis?

glycogen phosphorylase

47

What regulates the glycogenolysis and glycogenesis?

insulin/glucagon ratio and blood glucose levels

48

If the ratio of insulin/glucagon decreases, what occurs?

phosphorylation of glycogen phosphorylase to active state and the P of glycogen synthase to inactive state

49

What molecule is the key regulator for the direction of gluconeogenesis?

cAMP

50

T/F glycogen degradation is stimulated and synthesis is inhibited when the enzymes of glycogen metabolism are phosphorylated

true

51

Once cAMP activates PKA, what can occur wrt to glycogen synthesis and phosphorylase kinase?

If PKA phosphorylates glycogen synthase then glycogen synthesis is decreased

If PKA phosphorylates phosphorylase kinase then phoshphorylase b is activated to phosphorylase a which cleaves glucose residues from nonreducing ends of glycogen chains

52

What is produced when PKA phosphorylates phosphorylase kinase?

glucose 1-phosphate which is oxidized in the liver and converted to blood glucose

53

What is the major phosphatase involved in glycogen metabolism? describe its action and when it is used

Hepatic protein phosphatase 1 => removes phosphate groups from glycogen phosphorylase and glycogen synthase

-fasting => hepatic PP-1 is inactivated

54

What is the principle regulator of glycogen synthesis and degradation?

insulin

55

As neural signals to release epinephrine from the adrenal medulla, what will be the difference bw Beta receptors and alpha receptors?

Stimulation through beta receptors is similar to glucagon which activates PKA

stimulation through alpha receptors stimulates glycogenolysis in liver by increasing Ca levels

56

Describe the regulation of glycogenolysis in skeletal muscle

related to availability of ATP and only made when need for ATP is high

57

Why is skeletal muscle committed to the glycolytic pathway?

it has no glucose-6-phosphatase so G-6-P is committed to the glycolytic pathway

58

T/F AMP activates muscle glycogen phosphorylase but not liver glycogen phosphorylase

True

59

Describe the relationships from the stimuli of muscle contraction, nerve impulse and epinephrine

muscle: ATP => AMP => glycogen phosphorylase b => activated by phosphorylase kinase to yield => glycogen phosphorylase a
Nerve: Ca released => Ca-calmodulin => phosphorylase kinase
epinephrine=> cAMP => PKA => phosphorylase kinase