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Biochemistry Exam 3 > Chapter 25: Glycogen Synthesis > Flashcards

Chapter 25: Glycogen Synthesis Flashcards

1
Q

Glycogen degradation yields…

A

Glucose 1-Phosphate

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2
Q

Glycogen synthesis requires…

A

UDP-Glucose

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3
Q

What is UDP-Glucose?

Give:

  • full name
  • purpose
  • how it is synthesized
  • how it is rendered irreversible
A
  • Uridine diphosphate-glucose (activated form of glucose)
  • Is the glucose donor in glycogen synthesis.
  • Synthesized by UDP-Glucose pyrophosphorylase
  • The reaction is rendered irreversible by the hydrolysis of pyrophosphate
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4
Q

What catalyzes the transfer of glucose from UDP-Glucose to a growing chain?

A

Glycogen Synthase

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5
Q

Activated glucosyl unit of UDP-glucose is attached to glycogen by _____ catalyzed by _____.

A

Attached by a-1,4 glycosidic bond

Catalyzed by glycogen synthase

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6
Q

Glycogen synthesis requires an oligosaccharide of glucose residues as _____.

A

Primer (Need a chain of 7 or 8)

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7
Q

What synthesizes glycogen synthase’s primer?

A

Glycogenin - generates an oligosaccharide of glucose residues 8 molecules long. Considered a glucosyl transferase

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8
Q

Glycogen synthase can only synthesize _____.

A

a-1,4 linkages

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9
Q

A branching enzyme forms _____. What does this do?

A

a-1,6 linkages

Branching of glycogen increases its solubility and the rate of its synthesis and degradation.

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10
Q

Glycogen synthesis is regulated by?

A

Reversible phosphorylation

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11
Q

What is the key regulatory enzyme in glycogen synthesis?

A

Glycogen synthase

*Similar to glycogen phosphorylase but has the opposite effect

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12
Q

Glycogen synthase is _____ when in phosphorylated b form?

A

Inactive

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13
Q

Glycogen synthase is _____ when in unphosphorylated a form?

A

Active

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14
Q

Glycogen is an effective _____ of glucose.

A

Storage form

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15
Q

Only _____ is required to incorporate glucose 6-phosphate into glycogen.

A

One molecule of ATP

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16
Q

The complete oxidation of glucose derived from glycogen yields _____.

A

31 molecules of ATP

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17
Q

The overall efficiency of storage is nearly _____.

A

97%

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18
Q

Glycogen synthesis is inhibited by the same _____ and _____ that stimulate glycogen breakdown.

A

Glucagon and epinephrine signaling pathways

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19
Q

What stimulates glycogen breakdown and how?

A

Protein Kinase A (PKA) stimulates by phosphorylating and activating phosphorylase kinase

20
Q

How does PKA inhibit glycogen synthesis?

A

Inhibits by inactivating glycogen synthase by phosphorylation

21
Q

Glycogen synthase kinase also…

A

Phosphorylates and inhibits glycogen synthase

22
Q

Glycogen Degradation is _____ by phosphorylation.

A

Activated

23
Q

Glycogen Synthesis is _____ by phosphorylation.

A

Inhibited

24
Q

What reverses the regulatory effects of kinases on glycogen metabolism?

A

Protein Phosphatase 1 (PP1)

25
Q

PP1 _____ glycogen synthesis.

A

PP1 activates

26
Q

PP1 _____ glycogen degradation.

A

PP1 inhibits

27
Q

Insulin _____ glycogen synthesis. How?

A

Stimulates by inactivating glycogen synthase kinase (it’s kept unphosphorylated)

28
Q

In summary, glucagon and epinephrine regulate glycogen metabolism by:

A

G&E: Stimulating glycogen degradation

G&E: Inhibiting glycogen synthesis

29
Q

In summary, insulin regulates glycogen metabolism by:

A

I: Stimulating glycogen synthesis

I: Inhibiting glycogen degradation

30
Q

Low blood glucose levels means _____. This requires…

A

Hypoglycemia

Glucagon (starved or fasting state)

31
Q

High blood glucose levels means _____. This requires…

A

Hyperglycemia

Insulin (fed state)

32
Q

Diabetes is characterized by…

A

The presence of excess glucose and underutilization of glucose. This excess glucose is excreted in the urine.

33
Q

What happens with type 1 diabetes?

A

Insulin is not produced (10% of diabetic patients)

34
Q

What happens will type 2 diabetes?

A

Insulin is produced, but the insulin-signaling pathway is not responsive (insulin resistance)

35
Q

During diabetes, _____ is produced in excess.

A

Glucagon

36
Q

What is von Gierke disease (type I)?

A
  • Massive enlargement of the liver and hypoglycemia due to the lack of glucose 6-phosphatase from the liver.
  • Mutations in the gene encoding of the glucose 6-phosphate transporter also cause von Gierke disease
  • Cannot get into the ER lumen to produce glucose
37
Q

What is Cori disease (type III)?

A

Structure of liver and muscle glycogen abnormal and glycogen amount increased due to lack of debraching enzyme

38
Q

What is McArdle disease (type V)?

A
  • Results from defective muscle glycogen phosphorylase (Not able to degrade glycogen - losing ATP source)
  • Painful cramps occur when patients with McArdle disease exercise
  • Even when walking, they have muscle cramps due to lack of ATP
39
Q

A deficiency in the glycogen phosphorylase in liver would result in:

  • hemolytic anemia.
  • hyperglycemia.
  • hypoglycemia.
  • lactic acidosis.
  • muscle cramps.
A

Hypoglycemia

40
Q

The glycogen phosphorylase b in muscle is allosterically inhibited by high levels of:

  • AMP
  • NADH
  • fructose 2,6-bisphosphate
  • UDP-glucose
  • glucose 6-phosphate
A

Glucose 6-Phosphate

41
Q

T or F: Active protein phosphatase 1 (PP1) inhibits glycogen synthesis and stimulates glycogen degradation.

A

FALSE

42
Q

T or F: Glycogen synthesis requires UDP-glucose, an activated form of glucose.

A

TRUE

43
Q

T or F: Insulin stimulates glycogen synthesis by preventing the phosphorylation of glycogen synthase.

A

True

44
Q

T or F: Glycogen synthase requires an oligosaccharide of glucose residues as a primer, which is synthesized by the enzyme glycogenin.

A

True

45
Q

Diabetes mellitus results from _______________ insufficiency and _______________ excess.

  • epinephrine; insulin
  • glucagon; epinephrine
  • glucagon; insulin
  • leptin; epinephrine
  • insulin; glucagon
A

Insulin; glucagon

Biochemistry Exam 3 (10 decks)

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