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Biochemistry 2 > E2 Glycogenesis > Flashcards

E2 Glycogenesis Flashcards

1
Q

Define glycogenesis.

A

glycogen synthesis

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2
Q

The first step in glycogenesis is to phosphorylate glucose. What enzyme will facilitate this rxn (glucose —> G-6-P)?

A

hexokinase (m)/ glucokinase (L)

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3
Q

What will inhibit hexo/glucokinase?

A

the product

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4
Q

T/F. Step one of glycogenesis utilizes ATP.

A

true

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5
Q

The second rxn of glycogenesis, G-6-P —> G-1-P, is facilitated by what enzyme?

A

phosphoglucomutase

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6
Q

T/F. Phosphoglucomutase is also used in glycogenesis.

A

true

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7
Q

The third step of glycogenesis requires two enzymes. What are the enzymes?

  1. G-1-P + UTP + H2O —> UDP glucose +PPi
  2. PPi —> Pi + Pi
A
  1. UDP- glucose pyrophosphorylase

2. pyrophosphorylase

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8
Q

What is the name of activated glucose?

A

UDP-glucose

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9
Q

T/F. G-1-P + UTP + H2O to UDP-glucose + PPi is an irreversible rxn.

A

false

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10
Q

What will make G-1-P + UTP + H2O to UDP-glucose + PPi is an irreversible rxn?

A

hydrolyzing pyrophosphate quickly, which drives rxn toward producing UDP-glucose

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11
Q

When pyrophosphate is hydrolyzed, why does it make G-1-P + UTP + H2O to UDP-glucose + PPi is an irreversible rxn?

A

because it is liberating energy and lots of energy is needed to reverse the rxn

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12
Q

The fourth step of glycogenesis adds glucose to glycogen an forms alpha (1-4) bonds via what enzyme?

A

glycogen synthase

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13
Q

T/F. During the formation of alpha (1-4) bonds, glucose is added to reducing ends of glycogen.

A

false; non-reducing ends

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14
Q

In order to form alpha (1-4) bonds, we need glucose. Where does this glucose come from?

A

activated glucose (UDP-glucose)

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15
Q

The fifth step of glycogenesis deals with branching via what enzyme?

A

glycosyl (4:6) transferase

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16
Q

What are the two actions of glycosyl (4:6) transferase?

A
  1. break alpha (1-4) bonds

2. form alpha (1-6) bonds

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17
Q

What is the integral protein that will catalyze the formation of the “primer” of a glycogen granule?

A

glycogenin

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18
Q

Glycogenin is required to initiate a new glycogen granule, but what does glycogenin require?

A

tyrosine

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19
Q

Within a glycogen granule, each chain has how many glucose residues?

A

12-14

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20
Q

When glycosyl (4:6) transferase breaks alpha (1-4) bonds, a segment is transferred to a hydroxyl group on carbon #__ of a chain to form a branch.

A

6

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21
Q

What enzyme is the key regulatory enzyme of glycogenesis?

A

Glycogen synthase

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22
Q

How many forms of glycogen synthase are there? Name them.

A

2

  1. glycogen synthase a
  2. glycogen synthase b
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23
Q

What form of glycogen synthase is the active, non-phosphorylated form?

A

glycogen synthase a

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24
Q

T/F. Glycogen synthase b is active and phosphorylated.

A

False; b= inactive and phosphorylated

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25
Q

If glycogen synthase a is active, what state is it in?

A

R state

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26
Q

If glycogen synthase b is inactive, what state is it in?

A

T state (less active)

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27
Q

What are the three types of regulation for glycogenesis?

A
  1. allosteric regulation
  2. covalent modification
  3. reciprocal regulation
28
Q

Allosteric regulation of glycogenesis is activated by what enzyme?

A

glucose-6-phosphate

29
Q

What tissue types will you find allosteric regulation of glycogenesis?

A

Liver and Muscle

30
Q

T/F. Allosteric regulation is in a Fed state.

A

True

31
Q

What type of glycogenesis regulation prevents glycogenolysis from occurring at the same time as glycogenesis?

A

covalent modification

32
Q

What two hormones are associated with glycogenesis regulation?

A

glucagon and epinephrine

33
Q

T/F. Reciprocal regulation of glycogenesis will stimulate the CAMP cascade.

A

False; covalent modification

34
Q

What type of glycogenesis regulation states that the same conditions that stimulate glycogen breakdown will inhibit glycogen synthesis?

A

reciprocal regulation

35
Q

What two hormones stimulate glycogen breakdown?

A

epinephrine and glucagon

36
Q

What will stimulate protein phosphatase 1 (PP1)?

A

insulin and exercise

37
Q

What is the function of protein phosphatase 1 (PP1)?

A

dephosphorylates the enzymes

38
Q

When protein phosphatase 1 (PP1) dephosphorylates the enzymes, what enzymes become inactive? Active?

A

Inactive- glycogen phosphorylase and glycogen phosphorylase kinase
Active- glycogen synthase

39
Q

In the liver, PP1 is removing phosphate groups from glycogen synthase converting it to what form?

A

a form- active

40
Q

What hormone will cause PP1 to dephosphorylate the glycogen synthase converting it to the more active (a) form?

A

insulin

41
Q

When glycogen synthase is converted to the more active a form in liver, what process is stimulated?

A

glycogen synthesis (glycogenesis)

42
Q

If glucose binds to the active site on phosphorylase a, it will shift from _____ state to ______ state.

A

R state —> T State

43
Q

T/F. If glucose binds to the active site of phosphorylase a, glycogenesis in the liver is inhibited.

A

False; inhibits glycogen degradation

44
Q

In the muscle, what role does insulin have when it comes to glycogenesis?

A

when carbohydrate is available, we can stimulate glycogen synthesis to ensure we have fuel stored.

45
Q

T/F. It is not important to replenish our glycogen because there should be enough stored.

A

False

46
Q

What is the most potent stimulator of glycogen synthase in skeletal muscle?

A

low glycogen levels, like after exercise

47
Q

Low glycogen levels, like after exercise, is the most potent stimulator of what enzyme in skeletal muscle?

A

glycogen synthase

48
Q

What happens to glycogen synthase during low glycogen levels?

A

glycogen synthase, that is usually bound to the glycogen granule, is released when glycogen concentration falls

49
Q

After intense exercise, when is glycogen synthesis at the highest rate?

A

initially; first 30 minutes

50
Q

T/F. After intense exercise, glycogen synthesis rapidly declines to about 1/5th and then 1/9 by 60 minutes and 120 minutes respectively.

A

true

51
Q

What are the two reasons why glycogen synthesis rapidly declines with time?

A
  1. increased glucose uptake (GLUT4)

2. increased enzyme activity (glycogen synthase)

52
Q

T/F. In muscle, the rapid and slow phase are both insulin dependent.

A

False; rapid-independent

53
Q

When does the rapid phase of glycogenesis occur in the muscle?

A

30-60 minutes after exercise

54
Q

What two factors will stimulate the rapid phase of glycogenesis in the muscle?

A
  1. muscle glycogen levels are low

2. carb is provided immediately after exercise

55
Q

When does the slow phase of glycogenesis occur in the muscle?

A

after the rapid phase

56
Q

How long does the slow phase of glycogenesis last in the muscle?

A

can last a few hours

57
Q

T/F. The slow phase of glycogenesis only needs carbohydrates or insulin response in order to be stimulated.

A

false; must have carbohydrates available and insulin response

58
Q

T/F. Muscle glycogen synthesis rates may be 45% lower when carbohydrate ingestion post-exercise is delayed by 2 hours compared with immediate post-exercise consumption.

A

true

59
Q

Why do muscle glycogen synthesis rates lower when carbohydrate ingestion post-exercise is delayed by 2 hours compared with immediate post-exercise consumption?.

A

the number of glucose transporters associated with the sarcolemma returns to pre-exercise concentration

60
Q

What can be added to the diet to moderate carb intake?

A

protein/amino acids

61
Q

What function will adding protein/amino acids to moderate carb intake have on muscle?

A

higher muscle glycogen synthesis rates than carbohydrate alone

62
Q

T/F. If you have very high carbohydrate concentration and consumed protein, this will significantly increase glycogen synthesis rates.

A

False; if carbohydrate is very high, the protein doesn’t matter

63
Q

During carb loading, depleting glycogen reduces the power output of the muscle to ___%.

A

50%

64
Q

What is the purpose of carb loading?

A

super compensation: store glucose above normal storage amount

65
Q

What factors will stimulate glycogen phosphorylase to convert glycogen to G-1-P?

A
  1. low energy charge (Low ATP; High ADP/AMP)
  2. low levels of glucose
  3. epinephrine
  4. glucagon
  5. calcium
66
Q

What factors will stimulate glycogen synthase to convert G-1-P to glycogen?

A
  1. high energy charge (High ATP)
  2. high levels of glucose
  3. insulin
  4. low glycogen levels

Biochemistry 2 (14 decks)

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