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Flashcards in TCA Cycle Deck (87):
1

What is so special about the TCA cycle?

Major energy producing pathway in the body

2

Where does the TCA cycle occur?

Mitochondria

3

In what form does food product reach the TCA cycle?

Acetyl CoA

4

What is the general idea of the CA cycle?

Take Acetyl CoA and oxidize it to make carbon dioxide and water in order to make energy.

5

Where are all of the enzymes we need for the TCA cycle?

All the enzymes of the TCA cycle are in the mitochondrial matrix except succinate dehydrogenase, which is in the inner mitochondrial matrix

6

Acetyl CoA and ozaloacetate condense to form what?

Citrate

7

What enzyme condenses acetyl-CoA and oxaloacetate to make citrate?

Citrate synthase

8

Citrate is isomerized to what?

Isocitrate

9

What enzyme turns citrate to isocitrate?

Aconitase

10

Isocitrate is oxidized to what?

Alpha ketoglutarate

11

What two step process is involved in turning isocitrate to alpha ketoglutarate?

Oxidation
Decarboxylation

(CO2 is produced and the electrons are passed to NAD+ to form NADH and H+)

12

What enzyme turns isocitrate to alpha ketoglutarate?

Isocitrate dehydrogenase

13

What activates isocitrate dehydrogenase? Inhibits it?

This key regulatory enzyme of the TCA cycle is allosterically activated by ADP and inhibited by NADH

14

What happens to alpha ketoglutarate once it is made?

converted to succinyl-CoA

15

Alpha ketoglutarate to Succinyl-CoA is an example of what kind of reaction?

oxidative decarboxylation reaction

16

What enzyme turns alpha-ketoglutarate to succinyl CoA?

α-ketoglutarate dehydrogenase

17

What cofactors are required for α-ketoglutarate dehydrogenase?

This enzyme requires five cofactors: thiamine pyrophosphate, lipoic acid, CoASH, FAD, and NAD+

18

What happens to succinyl CoA?

cleaved to succinate

19

How do we get energy from the succinyl CoA to succinate reaction?

Cleavage of the high-energy thioester bond of succinyl-CoA provides energy for the substrate-level phosphorylation of GDP to GTP

20

What enzyme cleaves succinyl CoA to succinate?

succinate thiokinase aka succinyl-CoA synthetase

21

What happens to succinate?

oxidized to fumarate

22

What electron carrier is involved at the step where sucinate becomes fumarate?

succinate transfers two hydrogens together with their electrons to FAD, which forms FADH2

23

What enzyme oxidizes succinate to fumarate?

succinate dehydrogenase

24

Where does the succinate to fumarate rxn occur?

Inner mitochondrial membrane

25

What happens to fumarate?

Converted to malate

26

What enzyme turns fumarate to malate?

Fumarase

27

How does fumarase turn fumarate to malate?

Adds water across the double bond

28

What happens to malate?

Oxidized to regenerate oxaloacetate

29

What oxidizes malate to oxaloacetate?

Malate dehydrogenase

30

What enzyme carrier is involved with the malate dehydrogenase rxn?

two hydrogens along with their electrons are passed to NAD+, producing NADH and H+

31

How much ATP per NADH?

2.5 ATP

32

How much ATP per FADH2

1.5

33

How much ATP per turn of the TCA cycle?

1 mole of acetyl CoA gives us 10 moles of ATP

34

What happens during fasting?

Intermediates of the TCA cycle are utilized in the fasting state in the liver for the production of glucose and in the fed state for the synthesis of fatty acids

35

What are anaplerotic reactions?

Anaplerotic reactions replenish intermediates of the TCA cycle as they are removed for the synthesis of glucose, fatty acids, amino acids, or other compounds

36

One of the most important anaplerotic reactions?

Carboxylation of pyruvate to oxaloacetate

37

What enzyme carboxylates pyruvate to oxaloacetate?

pyruvate carboxylase

38

What cofactor does pyruvate carboxylase need?

Biotin

39

What activates the enzyme pyruvate carboxylase besides its cofactor biotin?

Acetyl-CoA

40

Where is pyruvate carboxylase found?

Liver
Brain
Adipose Tissue

41

What reactions do amino acids do to produce TCA intermediates?

Anaplerotic reactions

42

What amino acids form glutamate?

Glutamine, proline, arginine and histidine

43

What amino acid forms aspartate?

Asparagine

44

What becomes oxaloacetate?

Aspartate

45

Name of the reaction type that turns aspartate to oxaloacetate

Transamination

46

How is Succinyl CoA formed?

Propionyl-CoA gets converted to methylmalonyl-CoA and subsequently to Succinyl-CoA

47

Formation of propionyl CoA

You need Valine, isoleucine, methionine and threonine

48

What amino acids make fumarate?

Phenylalanine, tyrosine, and aspartate

49

What pathway slows down the TCA cycle?

Gluconeogenesis, which uses intermediates of the TCAcycle

50

What happens to the TCA cycle as glucose is synthesized?

malate or oxaloacetate is removed from the TCA cycle and replenished by anaplerotic reactions

51

Pyruvate is formed by what compounds?

Lactate or alanine

52

What product of the TCA cycle is important for fatty acid synthesis?

Citrate

53

What catalyzes the anaplerotic reactions that replenish the TCA cycle intermediates?

Pyruvate Carboxylase

54

How can we get amino acids from glucose via the oxaloacetate pathway?

Glucose is converted to pyruvate, which forms oxaloacetate, which by transamination forms aspartate and, subsequently, asparagine

55

How can we get amino acids from glucose via the oxaloacetate and acetyl CoA pathway?

Glucose is converted to pyruvate, which forms both oxaloacetate and acetyl-CoA, which condense, forming citrate. Citrate forms isocitrate and then α-ketoglutarate, from which glutamate, glutamine, proline, and arginine are produced

56

What accelerates the ETC?

When ADP levels are high relative to ATP the reactions of the electron transport chain are accelerated.

57

What speeds up the TCA cycle?

NADH is rapidly oxidized by the ETC; consequently, the TCA cycle speeds up

58

What slows down the ETC?

When the concentration of ATP is high the electron transport chain slows down

59

What slows down the TCA cycle?

When the concentration of ATP is high the electron transport chain slows down, NADH builds up, and consequently the TCA cycle is inhibited

60

How, specifically, does the TCA cycle slow down (this is very involved, but think about the process)

NADH allosterically inhibits isocitrate dehydrogenase. Isocitrate accumulates, and because the aconitase equilibrium favors citrate, the concentration of citrate rises. Citrate inhibits citrate synthase, the first enzyme of the cycle.

61

What happens to oxaloacetate when NADH is high?

Oxaloacetate is converted to malate when NADH is high and, therefore, less substrate (OAA) is available for the citrate synthase reaction

62

What reactions are NAD used in?

isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and malate dehydrogenase reactions

63

What is niacin important for?

Niacin is used for the synthesis of the nicotinamide portion of NAD

64

What is important for the production of FAD?

Riboflavin

65

What is thiamine important for?

the synthesis of thiamine pyrophosphate

66

Importance of Pantothenate?

synthesis of CoASH

67

Effects of low Vitamin A

Night blindness and xerophthalmia

68

Effects of low Vitamin D

Inadequate bone mineralization, rickets in children

69

Effects of low Vitamin E

Reproductive failure, muscular dystrophy, neurologic abnormalities

70

Effects of low Vitamin K

Defective blood coagulation

71

Effects of low Vitamin C

Scurvy

72

Effects of low thiamine?

Berriberi

73

Effects of low riboflavin?

Oral-buccal cavity lesions

74

Effects of low niacin?

Pellagra (diarrhea, dermatitis, dementia, death)

75

Effects of low Vitamin B6

Convulsions, dermatitis, anemia

76

Effects of low Folate

Megaloblastic Anemia

77

Effects of low Vitamin B12?

Megaloblastic Anemia and neurological symptoms

78

Effects of low biotin

Anorexia, nausea, vomitis, glossitis, alopecia

79

Effects of low pantothenic acid

Listlessness, fatigue, burning feet syndrome

80

How do Carbons from glucose enter the TCA cycle?

In order for carbons from glucose to enter the TCA cycle, glucose is first converted to pyruvate by glycolysis, then pyruvate forms acetyl-CoA

81

How is acetyl CoA formed?

Pyruvate dehydrogenase catalyzes the oxidative decarboxylation of pyruvate, forming acetyl-CoA

82

Where is pyruvate dehydrogenase?

Pyruvate dehydrogenase, a multienzyme complex located exclusively in the mitochondrial matrix

83

What is similar between pyruvate dehydrogenase and alpha ketoglutarate?

They need the same 5 components

84

What is different between pyruvate dehydrogenase and alpha ketoglutarate?

In contrast to α-ketoglutarate dehydrogenase, a pyruvate dehydrogenase exists in a phosphorylated (inactive) form and a dephosphorylated (active) form

85

How is pyruvate decarboxylase deactivated?

CoASH and NAD+. Can also be inactivated by ADP

86

What activates the pyruvate decarboxylase?

The products of the pyruvate dehydrogenase reactions, acetyl-CoA and NADH. It is activated specifically by a phosphatase

87

How is pyruvate decarboxylase controlled, generally?

When the concentration of substrates is high, the dehydrogenase is active, and pyruvate is converted to acetyl-CoA. When the concentration of products is high, the dehydrogenase is relatively inactive