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Biochem > Metabolism > Flashcards

Metabolism Flashcards

1
Q

How many ATPs are generated in cells that use the malate-aspartate shuttle

A

32 ATP per glucose

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2
Q

How many ATPs are generated in cells that use the glycerol-3-phosphate shuttle

A

30 ATP per glucose

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3
Q

What cells use malate-aspartate shuttle

A

Heart, liver, kidneys

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4
Q

What cells use the glycerol-3-phosphate shuttle

A

Brain, skeletal muscle

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5
Q

Where are GLUT-3 transporters located

A

Neurons, placenta

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6
Q

What GLUT transporter is responsible for fructose uptake in GI tract

A

GLUT-5

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7
Q

What enzymes can phosphorylate glucose thereby trapping it in the cell?

A

Hexokinase

Glucokinase

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8
Q

What cells have glucokinase

A

Cells that regulate glucose - Liver, beta cells of pancreas

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9
Q

What is the Km of glucokinase

A

Very HIGH - needs a lot of glucose around to work

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10
Q

What is the Vmax of glucokinase

A

Very high - once it starts working, it works quickly and efficiently

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11
Q

What is the Km of hexokinase

A

Very low - high affinity for glucose

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12
Q

Why is the Km of hexokinase low

A

So that even when glucose concentration is low it can still trap glucose that does come in

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13
Q

Which of the two enzymes that make glucose-6-phosphate are induced by insulin?

A

Glucokinase

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14
Q

What is the Vmax of hexokinase

A

Low

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15
Q

Why is the Vmax of hexokinase low

A

It has a lower capacity

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16
Q

Which of the two enzymes that make glucose-6-phosphate is feedback inhibited by glucose-6-P

A

Hexokinase

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17
Q

Which of the two enzymes that make glucose-6-phosphate is associated with maturity-onset diabetes of the young (MODY)?

A

Glucokinase

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18
Q

What enzyme catalyzes conversion of fructose-6-phosphate to fructose 1,6 bisphosphate

A

Phosphofructokinase-1

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19
Q

What is the rate limiting enzyme of glycolysis

A

PFK-1

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20
Q

What stimulates PFK-1

A

AMP (low energy)

Fructose 2,6 bisphosphate

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21
Q

What inhibits PFK-1

A

ATP (high energy states)

Citrate (substrate of TCA cycle)

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22
Q

What enzyme converts phosphoenolpyruvate to pyruvate?

A

Pyruvate kinase

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23
Q

What stimulates pyruvate kinase

A

Fructose 1,6 bisphosphate

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24
Q

What inhibits pyruvate kinase

A

ATP and alanine (indicate you already have a lot of energy)

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25
Q

What is the presentation of pyruvate kinase deficiency

A

Hemolytic anemia

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26
Q

Why is hemolytic anemia a presentation in pyruvate kinase deficiency

A

Inability to maintain Na/K ATPase means RBC’s swell and lyse

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27
Q

What’s the most common glycolytic enzyme deficiency

A

Pyruvate kinase deficiency

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28
Q

A muscle biopsy reveals elevated glycogen levels, elevated fructose-6-phosphate, and decreased pyruvate. What enzyme deficiency do you suspect?

A

PFK -1

Because there is a buildup of its substrate which is fructose-6-phosphate

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29
Q

What makes fructose 2,6 bisphosphate

A

PFK-2 makes it from fructose-6-phosphate

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30
Q

What is PFK-2

A

Catalyzes formation of fructose 2,6 bisphosphate from fructose-6-phosphate

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31
Q

What are the two products fructose-6-phosphate could be converted to?

A

Fructose 1,6 bisphosphate (PFK1)

Fructose 2,6 bisphosphate (PFK2)

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32
Q

What stimulates PFK-2 production

A

Fed state - insulin

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33
Q

How does insulin stimulate glycolysis?

A

Indirectly: It stimulates PFK2 to make more fructose 2,6 bisphosphate, which stimulates PFK-1

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34
Q

How does glucagon promote gluconeogenesis

A

It stimulates Fructose bisphosphatase 2, which creates fructose-6-phosphate and opposes the opposite reaction by PFK2. Fructose 6 phosphate then goes on to gluconeogenesis

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35
Q

What is the action of fructose bisphosphatase 2

A

Opposes PFK 2

Converts fructose 2,6 bisphosphate to fructose 6 phosphate

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36
Q

How does glucagon stimulate fructose bisphosphatase 2?

A

Glucagon binds Glucagon receptor –> AC –> cAMP pathway

cAMP phosphorylates PKA which phosphorylates PFK-2/FBP-2 complex. This results in active FBP-2 and inactive PFK-2

37
Q

What is the configuration of PFK-2/FBP-2 when PKA gets activated by glucagon

A

It is phosphorylated by PKA and FBP-2 is active and PFK-2 is inactive

38
Q

How does PKA get shut off so that PFK-2/FBP-2 configuration has active PFK-2 and glycolysis is favored?

A

High insulin glucagon ration so glucagon receptor not stimulated and PKA not activated by cAMP

39
Q

What enzymes convert glucose to glucose 6 phosphate?

A

Hexokinase and glucokinase (liver and beta cells)

40
Q

How do you get backwards in gluconeogenesis from pyruvate to phosphoenolpyruvate?

A
  1. Pyruvate carboxylase with biotin makes oxaloacetate

2. Oxaloacetate –> PEP via PEP carboxykinase

41
Q

What coenzyme does pyruvate carboxylase require

A

Biotin

42
Q

What stimulates the creation of oxaloacetate from pyruvate in gluconeogenesis?

A

Acetyl CoA

43
Q

How is F-1,6-BP converted back to F-6-P in gluconeogenesis?

A

Fructose 1,6 bisphosphatase

44
Q

What stimulates F-1,6-BP?

A

ATP

45
Q

What is rate limiting enzyme in gluconeogenesis?

A

Fructose 1,6 bisphosphatase

46
Q

What inhibits F-1,6-BP

A

AMP, Fructose 2,6 bisphosphatase

47
Q

What converts glucose 6 phosphate to glucose

A

Glucose 6 phosphatase

48
Q

What are the 4 unique enzymes of gluconeogensis

A
  1. Pyruvate carboxylase
  2. PEP carboxykinase
  3. Fructose 1,6 bisphosphatase - rate limiting
  4. Glucose 6 phosphatase
49
Q

Where does gluconeogenesis take place?

A

Cells that have glucose 6 phosphatase
Hepatocytes
Kidney
Intestinal epithelium

50
Q

When does gluconeogenesis take place

A

Whenever blood glucose is low

51
Q

What are the two things hepatocytes do when blood glucose is low?

A
  1. Share glycogen stores

2. Convert other molecules into pyruvate and use that pyruvate to make glucose

52
Q

What molecules can be converted to pyruvate to enter gluconeogenesis?

A

Odd chain FA’s - make propionyl CoA
TCA molecules (–> oxaloacetate)
Some AA’s

53
Q

What enzyme catalyzes reaction of glucose-1-P to UDP Glucose?

A

UDP-glucose pyrophosphorylase

54
Q

What molecule attaches UDP Glucose to the expanding glycogen molecule

A

Glycogen synthase

55
Q

What is the rate limiting enzyme in glycogen synthesis

A

Glycogen synthase

56
Q

What kind of linkages does glycogen synthase make

A

Alpha 1,4 glycosidic linkages

57
Q

What enzyme makes branches in glycogen

A

Branching enzyme

58
Q

What kind of linkages does branching enzyme make

A

Alpha 1,6 glycosidic linkages

59
Q

What enzyme breaks down alpha 1,4 glycosidic linkages

A

Glycogen phosphorylase

60
Q

What inhibits glycogen phosphorylase?

A

ATP, Glucose, G-6-P

61
Q

What enzyme converts glucose 1-P to glucose 6-P

A

Phosphoglucomutase

62
Q

What enzyme converts Glucose 6-P to glucose in glycogenolysis

A

Glucose-6-Phosphatase (also the last step in gluconeogenesis pathway)

63
Q

How are alpha 1,6 glycosidic linkages broken down?

A

Debranching enzyme: alpha 1,6 glucosidase

64
Q

What are the two functions of debranching enzyme

A
  1. Transferase (transfer 3 last G-1-Ps to end)

2. Cleaving

65
Q

How does insulin regulate glycogen storage?

A

Insulin inhibits glycogen phosphorylase

Insulin stimulates glycogen synthase

66
Q

What happens in a high stress state to glycogen?

A

Epinephrine and glucagon are released

67
Q

How does epinephrine release glucose?

A

Stimulates b-adrenergic receptors which similarly release cAMP , activates glycogen phosphorylase like glucagon

68
Q

What enzyme is deficient in McArdle disease

A

Glycogen phosphorylase (found in muscle)

69
Q

What are the symptoms of McArdle disease

A

Lots of glycogen in the muscle that cannot be broken down leads to painful cramps, myoglobinuria, and arrhythmia. Cells swell and lyse (rhabdomyolysis).

70
Q

What enzyme is deficient in Von Gierke disease

A

Glucose-6-phosphatase (converts glucose-6P to glucose in gluconeogenesis and glycogenolysis)
This doesn’t affect skeletal muscle, recall - only affects glucose-sharing cells

71
Q

What are the symptoms of Von Gierke disease

A

Severe fasting hypoglycemia (can’t share glucose), high amounts of glycogen in liver, high blood lactate, and hepatomegaly, kidney enlargement

72
Q

What is the treatment of Von Gierke disease

A

Frequent oral glucose, cornstarch

Avoid fructose and galactose

73
Q

What enzyme is deficient in Cori disease

A

Deficient debranching enzyme alpha 1,6 glucosidase

74
Q

What are symptoms of Cori disease

A

Milder Von Gierke

Gluconeogensis intact

75
Q

What enzyme is deficient in Pompe disease

A

Deficiency of alpha 1,4 glucosidase in lysosomes

76
Q

What are the symptoms of Pompe disease

A 
Infantile form: 
Severe muscle weakness
Cardiomegaly and heart failure
Shortened life expectancy
Adult form: Some enzyme activity; gradual weakness and respiratory failure
77
Q

Glycogen phosphorylase deficiency

A

McArdle disease

78
Q

Glucose 6 Phosphatase deficiency

A

Von Gierke disease

79
Q

Lactic acidosis, hyperlipidemia, hyperuricemia

A

Von Gierke disease

80
Q

Alpha 1,6 glucosidase deficiency

A

Cori Disease

81
Q

Alpha 1,4 glucosidase deficiency

A

Pompe disease

82
Q

Increased glycogen in the liver with severe fasting hypoglycemia

A

Von Gierke disease

83
Q

Hepatomegaly, hypoglycemia, hyperlipidemia (normal kidneys, lactate, and uric acid)

A

Cori disease

84
Q

Severe hepatosplenomegaly with enlarged kidneys

A

Von Gierke disease

85
Q

Painful muscle cramps, myoglobinuria with strenuous exercise

A

McArdle’s disease

86
Q

How is Cori disease (debranching enzyme deficiency) different from other glycogen storage diseases

A

In cori disease see accumulation of short dextrin structures in cytosol of hepatocytes, without fatty infiltration of the liver.

87
Q

Hepatic steatosis glycogen storage disease

A

Von Gierke’s (glucose-6-phosphatase deficiency)

88
Q

What glycogen storage disease does not present with hypoglycemia

A

Pompe’s disease (lysosomal enzyme acid maltase deficiency)

89
Q

How does glycogen phosphorylase deficiency present

A

McArdle’s syndrome

Decreased exercise tolerance, muscle pain and cramping in exercise, and myoglobinuria

Biochem (10 decks)

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