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2) Biochemistry II > Regulation of Glycogen Metabolism > Flashcards

Regulation of Glycogen Metabolism Flashcards

1
Q

What is energy storage in animals? What about plants?

A

Animals: glycogen
Plants: starch

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2
Q

Where is glycogen primarily found? How is it stored?

A
  • Liver (10%) and muscle (1-2%)

- Stored in granules

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3
Q

What are the two types of starch granules?

A
  • a-rosettes (contain 20-40 B-particles)

- B-particles (contain glucose with many reducing ends)

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4
Q

Glycogen is depleted after _________ of fasting in the liver, and ______ of strenuous exercise in muscle

A

12 to 24 hours

1 hour

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5
Q

Is there more glycogen storage or fat storage?

A

More fat storage

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6
Q

What other tissues store glycogen?

A

Astrocytes (nervous system), heart, and adipose tissue

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7
Q

What is glycogenesis?

A

The synthesis of glycogen

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8
Q

Where does glycogenesis take place?

A

Can take place in any cells that store glycogen, but predominant in liver cells

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9
Q

What is the precursor for glycogenesis?

A

UDP-Glucose (sugar nucleotide)

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10
Q

What are the two steps to glycogenesis?

A

1) Formation of UDP-Glucose

2) Formation of the initial short-chains

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11
Q

What does the formation of UDP-Glucose require? Which enzyme catalyzes this step?

A
  • UTP + Glucose

- NDP-Sugar pyrophosphorylase

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12
Q

What does NDP-Sugar pyrophosphorylase do?

A
  • Removes 2 phosphate groups from the nucleotide triphosphate and adds a sugar
  • Creates UDP-Glucose
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13
Q

What happens to the pyrophosphate created during the formation of UDP-Glucose?

A

The pyrophosphate is unstable and is quickly converted to an organic phosphate

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14
Q

What catalyzes the formation of initial short-chains?

A

Glycogenin (protein)

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15
Q

What does glycogenin contain at the 194th position?

A

Tyrosine, which has an OH- group

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16
Q

What does the OH- group of glycogenin attack? What does that form?

A
  • OH- group of glycogenin attacks the 1st carbon of UDP-Glucose
  • Glucosyltransferase activity adds a glucosyl group in the form of glucose, creating a glycogenin and glucose complex
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17
Q

OH- group of the __ carbon can attack the __ carbon on the next UDP-glucose, which creates a _____ glycosidic bond

A

4
1
1-4

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18
Q

The chain-extending activity of glycogenin can repeat itself ___ more times, and contain maximum __ carbons

A

6

8

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19
Q

The elongation of glycogen is catalyzed by what? What is the precursor?

A
  • Glycogen synthase

- UDP-glucose

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20
Q

What does glycogen synthase require?

A

Requires a short-chain that contains at least 4 glucose molecules

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21
Q

What bond does glycogen synthase create?

A
  • Bond between the 4th carbon of the non-reducing end
    of the glycogen chain and the 1st carbon of UDP-Glucose
  • The 4th carbon of the new glucose now has a non-reducing end
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22
Q

The branching of glycogen is catalyzed by what?

A

Glycogen-branching enzyme

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23
Q

What does glycogen-branching enzyme do? What does it create?

A
  • Attacks the 4th glycosidic bond and cleaves the long-chain, which reattaches from the 4th glucose
    molecule of the new non-reducing end
  • Creates a 1-6 glycosidic bond
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24
Q

Branching (increases/decreases) water-solubility, and creates _______

A

increases

new non-reducing ends

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25
Q

Why are non-reducing ends important?

A

Non-reducing ends are important when glucose is synthesized from the breakdown of glycogen

26
Q

What are the four steps to glycogenesis and their enzymes?

A
  1. Formation of UDP-Glucose (NDP-sugar pyrophosphorylase)
  2. Initial short-chain synthesis (Glycogenin)
  3. Elongation (Glycogen Synthase)
  4. Branching (Glycogen-Branching Enzyme)
27
Q

What is glycogenlysis? What is the end-product?

A
  • Breakdown of glycogen to yield glucose

- Creates Glucose 1-phosphate as an end-product

28
Q

What catalyzes glycogenolysis?

A

Glycogen phosphorylase

29
Q

Glycogen phosphorylase can only act where?

A

At the non-reducing end of glycogen

30
Q

What does glycogen phosphorylase do?

A

Breaks the 1-4 glycosidic bond and adds a free inorganic

phosphate group

31
Q

Where does the free inorganic phosphate for glycogen phosphorylase come from?

A

The free inorganic phosphate comes from a store, and

NOT from ATP; does not require additional energy

32
Q

What acts as a cofactor for glycogen phosphorylase?

A

Pyridoxal phosphate

33
Q

What are the three enzymes of glycogenolysis?

A
  1. Glycogen phosphorylase: breaks the 1-4 glycosidic bond
  2. Glycogen debranching enzyme: breaks the 1-6 glycosidic bond
  3. Phosphoglucomutase
34
Q

Glycogenolysis debranching enzyme has two types of activities. What are they?

A
  • Transferase activity

- Glucosidase activity

35
Q

What is the transferase activity of the debranching enzyme?

A

Removes the 3 glucose units, and attaches it to the non-reducing end of the longer branch (yellow), leaving one glucose attached with a 1-6 glycosidic bond

36
Q

What is the glucosidase activity of the debranching enzyme?

A
  • Cleaves the 1-6 glycosidic bond, which removes a glucose
  • The long-chain no longer has a branch, and is available for
    glycogen phosphorylase to continue
37
Q

What is the role of phosphoglucomutase?

A
  • Catalyzes the formation of Glucose 6-Phosphate from Glucose 1-Phosphate
  • Transfers the phosphate group from carbon 1 to carbon 6
38
Q

Phosphoglucomutase must be _______ to function

A

phosphorylated

39
Q

How does phosphoglucomutase work?

A
  • The phosphorylated serine donates its phosphate groups to the 6th carbon, which now contains two phosphate groups: Glucose 1,6-bisphosphate
  • The phosphate group at the 1st carbon is given back to the serine (recycling), leaving behind Glucose 6-Phosphate, which is a metabolite for glycolysis
40
Q

Where is glucose-6-phosphate dephosphorylated?

A

In the liver

41
Q

Glucose 6-phosphate is created in the _______, and is brought to the ___ through the ________ transporter

A

cytoplasm
ER
G6P transporter (T1)

42
Q

In the ER, what dephosphorylates G6P? What does that create?

A
  • Glucose-6-phosphatase

- Creates a free glucose and an inorganic phosphate, which can be thrown out of the ER

43
Q

______ glucose cannot pass through GLUT transporters

A

phosphorylated

44
Q

Does muscle contribute to blood glucose concentration? Why?

A

No since it does not express Glucose 6-phosphatase

45
Q

Phosphorylase a is the _____ form, which happens when it is ________

A

active

phosphorylated

46
Q

Phosphorylase b is the ______ form, which happens when it is _______

A

inactive

dephosphorylated

47
Q

What is the role of phosphorylase a?

A

Cleaves individual glucose molecules from glycogen

48
Q

What enzyme transforms phosphorylase b to phosphorylase a? What enzyme transforms phosphorylase a to phosphorylase b?

A

b –> a: phosphorylase b kinase

a –> b: phosphorylase a phosphatase (PP1)

49
Q

What is phosphorylase b kinase activated by?

A
  • Epinephrine
  • Ca2+
  • AMP (muscle)
  • Glucagon (liver)
50
Q

What is phosphorylase a phosphatase activated by?

A

Insulin

51
Q

Glucagon receptors are present in ______, while epinephrine receptors are present in _______

A

hepatocytse

myocytes

52
Q

The activation of glycogen phosphorylase a through GPCR receptors leads to an increase in what?

A

G1P, and eventually G6P and glucose

53
Q

Glycogen synthase is active when it is (phosphorylated/dephosphorylated)

A

dephosphorylated

54
Q

Phosphorylation of glycogen synthase occurs where?

A

At 3 serine residues

55
Q

What activates glycogen synthase?

A
  • Insulin
  • G6P
  • Glucose
56
Q

How does insulin activate glycogen synthase?

A

Inhibits GSK3, which inhibits the phosphorylation of GS

57
Q

What inactivates glycogen synthase?

A
  • Glucagon

- Epinephrine

58
Q

Glucagon is only present in _______, while epinephrine is present in ______ and _______

A
  • liver cells
  • liver cells
  • muscle cells
59
Q

Glycogenolysis is promoted in which cell type(s)?

A

Both (liver and muscle cells)

60
Q

Glycolysis is promoted in which cell type(s)?

A
  • Promoted in muscle cells

- Inhibited in liver cells by PKA

61
Q

Why is glycolysis promoted in muscle cells, but inhibited in liver cells?

A
  • Muscle cells lack the glucagon receptor

- Muscle cells do NOT produce F26BP, which is involved in the inhibition of glycolysis

62
Q

Glucogeogenesis is promoted by ______, which can only happen in _____ cells

A

glucagon

liver

2) Biochemistry II (23 decks)

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