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MBOD Block 4 > Glycogen Metabolism > Flashcards

Glycogen Metabolism Flashcards

1
Q

What is the main storage form of glucose?

A

Glycogen

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2
Q

Where are the largest amounts of glycogen found?x

A

Liver and skeletal muscle

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3
Q

Does glycogenesis require energy? Glycogenolysis?

A

Yes, no

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4
Q

What is glycogen made of?

A

Alpha 1-4 and alpha 1-6 glycosidic linkages

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5
Q

Where are branches formed?

A

At alpha-1,6-bonds

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6
Q

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

A

Glycogenin

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7
Q

Can glycogen be degraded rapidly?

A

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

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8
Q

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

A

Glucose for blood; glucose for ATP use in muscle contraction

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9
Q

Does muscle have G6Pase?

A

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

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10
Q

What provides energy for glycogenesis?

A

UTP

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11
Q

What is the glucose donor in glycogen synthesis?

A

UDP-Glucose

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12
Q

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

A

Glycogen synthase, amylo 4-6 transferase

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13
Q

What is the regulated step in glycogen degradation?

A

Glycogen phosporylase

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14
Q

What removes 3 glucosyl residues from glycogen (debranching enzyme)

A

Transferase

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15
Q

What hydrolyzes alpha 1,6 glycosidic linkages ?

A

A-1-6- Glucosidase

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16
Q

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

A

True

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17
Q

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

A

Yes, No

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18
Q

What removes phosphates from glycogen phosphorylase & glycogen synthase?

A

Hepatic protein phosphatase 1

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19
Q

In fasting is the answer to #423 active?

A

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

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20
Q

Does AMP activate liver glycogen phosphorylase?

A

No, Only in muscle

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21
Q

Does glucose inhibit glycogen phosphorylase in muscle?

A

No, Only in liver

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22
Q

Describe GSD Type I along with location

A

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

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23
Q

Describe GSD Type II along with location

A

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

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24
Q

Describe GSD Type III along with location

A 
Debranching deficiency (Cori’s disease), hepatomegaly, dx. By excessive branched glycogen in urine
Location: liver, skeletal muscle, heart
25
Q

Describe GSD Type IV along with location

A

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

26
Q

Describe GSD Type V along with location

A

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
Q

Describe GSD Type VI along with location

A

Liver phosphorylase deficiency

28
Q

Describe GSD Type VII along with location

A

Muscle PFK-1 deficiency (elevated F26BP and G6P)

29
Q

Describe GSD Type IX along with location

A

Liver phosphorylase kinase defect

30
Q

Describe GSD Type X along with location

A

PKA, cAMP dependent defect

31
Q

What pathways are affected when glucagon is released? How?

A

increase in glycogenolysis, gluconeogenesis, lipolysis

Decrease in liver glycolysis

32
Q

What pathways are affected when insulin is released? How?

A

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

33
Q

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

A

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

at the alpha-1,6-bonds

34
Q

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

A

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

35
Q

What produced the branches of glycogen?

A

the branching enzyme => glucosyl 4,6 transferase

36
Q

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

A

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

37
Q

What does glycogen degradation produce?

A

glucose 1-phosphate as major product but also free glucose

38
Q

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

A

skeletal muscle

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

39
Q

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

A

liver

glucagon and epinephrine

40
Q

T/F synthetic pathway requires energy from ATP

A

false, UTP

41
Q

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

A

glucose -1- Phosphate

42
Q

What are the stages of glycogen synthesis?

A
  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
Q

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

A

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

44
Q

Describe the primer used in glycogen synthase activity

A

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
Q

What are the steps in glycogen degradation?

A
  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
Q

What is the regulated step of glycogenolysis?

A

glycogen phosphorylase

47
Q

What regulates the glycogenolysis and glycogenesis?

A

insulin/glucagon ratio and blood glucose levels

48
Q

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

A

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

49
Q

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

A

cAMP

50
Q

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

A

true

51
Q

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

A

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
Q

What is produced when PKA phosphorylates phosphorylase kinase?

A

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

53
Q

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

A

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

-fasting => hepatic PP-1 is inactivated

54
Q

What is the principle regulator of glycogen synthesis and degradation?

A

insulin

55
Q

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

A

Stimulation through beta receptors is similar to glucagon which activates PKA

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

56
Q

Describe the regulation of glycogenolysis in skeletal muscle

A

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

57
Q

Why is skeletal muscle committed to the glycolytic pathway?

A

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

58
Q

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

A

True

59
Q

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

A

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

MBOD Block 4 (15 decks)

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