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BIO1332 - Biochemistry > Citric Acid Cycle > Flashcards

Citric Acid Cycle Flashcards

1
Q

What is another name for citric acid cycle?

A

Krebs cycle or tricarboxylic acid (TCA)

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2
Q

What does the citric acid cycle lead to?

A

Oxidative phosphorylation

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3
Q

Where is the citric acid cycle carried out?

A

Mitochondrial matrix

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4
Q

Where is glycolysis carried out?

A

In cytoplasm

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5
Q

What does pyruvate dehydrogenase complex do?

A

Pyruvate is converted to Acetyl CoA by

pyruvate dehydrogenase

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6
Q

What is pyruvate dehydrogenase complex ?

A
  • Multi enzyme complex
  • Consists of an aggregate of three different enzymes
  • Coenzymes and regulatory molecules
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7
Q

What is pyruvate dehydrogenase complex molecular mass?

A

4 – 10 million daltons

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8
Q

How can you view pyruvate dehydrogenase complex ?

A

Under an electron microscopy

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9
Q

Why is Pyruvate dehydrogenase complex

a complex?

A

Physical proximity prevents release of
intermediates
Each catalyses a part of the reaction from pyruvate to Acetyl CoA

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10
Q

What are the three different enzymes in a pyruvate dehydrogenase complex?

A

E1 E2 E3

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11
Q

What is E1?

A

Pyruvate dehydrogenase

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12
Q

What reaction does E1 catalyse?

A

Oxidative decarboxylation of pyruvate

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13
Q

What is the Cofactor of E1?

A

Thiamine pyrophosphate

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14
Q

What is E2?

A

Dihydrolipoyl transacetylase

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15
Q

What is E3?

A

Dihydrolipoyl dehydrogenase

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16
Q

What reaction does E2 catalyse?

A

Transfer of the acetyl group to CoA

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17
Q

What reaction does E3 catalyse?

A

Regeneration of the oxidised form of lipoic acid

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18
Q

What is the cofactor of E2?

A

Lipoic acid

Coenzyme A

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19
Q

What is the cofactor of E3?

A

FAD

NAD+

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20
Q

Pyruvate + CoA + NAD+ produces…

A

acetyl CoA + CO2 + NADH

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21
Q

What is the citric cycle about?

A

Not proaction of ATP

But removal of electrons and reducing of NADH

22
Q

How many steps are there in the citric acid cycle?

A

8

23
Q

What is the first step of the citric acid cycle?

A

1: The acetyl group is carried to the citric acid cycle by CoA

Condensation of oxaloacetate and acetyl CoA is catalysed by citrate synthase

Citrat produced (6C)

24
Q

What is the second step of the citric acid cycle?

A

2: Isomeration of citrate

Isomerisation of citrate to isocitrate is catalysed by aconitase in two steps

The iron facilitates the hydration/hydration reactions during intermediate step

25
Q

What is the third step of the citric acid cycle?

A

3: Oxidation and decarboxylation of isocitrate

Isocitrate is oxidised and decarboxylated by isocitrate dehydrogenase in a two step process

26
Q

How is the third stage of the citric acid cycle controlled?

A

Allosterically activated by ADP and inhibited by ATP

27
Q

What is the fourth step of the citric acid cycle?

A

4: Oxidation and decarboxylation of α-Ketoglutarate

α-Ketoglutarate is oxidised and decarboxylated by α-Ketoglutarate dehydrogenase complex

CoA is required in the reaction similar to the pyruvate dehydrogenase complex

28
Q

What is the fifth step of the citric acid cycle?

A

5: Cleavage of succinyl CoA

The high energy thioester bond is cleaved by succinyl CoA synthetase

Release of CoA is coupled to phosphorylation of GDP to GTP leading to phosphorylation of ADP generating ATP

29
Q

Which stages 1-8 is ATP produced in the citric acid cycle?

A

Stage 5

30
Q

What is the sixth step of the citric acid cycle?

A

6: Oxidation of succinate

Succinate is oxidised to fumarate by succinate dehydrogenase

The two electrons and two protons removed are transferred to coenzyme FAD generating FADH2

31
Q

What is the seventh step of the citric acid cycle?

A

7: Hydration of fumarate

Fumarate is hydrated to malate by fumarase

The reaction requires the addition of H2O

32
Q

What is the eighth step of the citric acid cycle?

A

8: Oxidation of malate

Malate is oxidised to oxaloacetate by malate dehydrogenase

Third (and final) production of NADH + H+

33
Q

How is the Krebs cycle negatively regulated?

A

By the concentrations of ATP and NADH

34
Q

How is the kerbs cycle positively regulated?

A

By the concentration of ADP

35
Q

What are control points?

A

Enzymes

36
Q

What are the key enzymes in control of regulating the citric acid cycle?

A

Pyruvate dehydrogenase
Isocitrate dehydrogenase
a-Ketoglutarate dehydrogenase

37
Q

What does a-Ketoglutarate dehydrogenase do to regulate the citric acid cycle?

A

inhibited by ATP, succinyl CoA and NADH

38
Q

What does Isocitrate dehydrogenase do to regulate the citric acid cycle?

A

inhibited by ATP and NADH

39
Q

What does Pyruvate dehydrogenase dehydrogenase do to regulate the citric acid cycle?

A

Irreversible reaction.

Inhibited by ATP, acetyl CoA and NADH.

40
Q

How do arsensic and mercury regulate the citric acid cycle?

A

Inhibits pyruvate dehydrogenase complex by inactivating the dihydrolipomide component of the transacetylase (E2).

41
Q

How many carbons enter the citric acid cycle?

A

2 (4 really as two pyruvates were produced in glycolysis)

42
Q

How many carbons leave the citric acid cycle?

A

2 (4 really as two pyruvates were produced in glycolysis)

43
Q

How many FADH2 molecules produced? How many electrons?

A

1 (2)

2 (4)

44
Q

How many NADH molecules produced?

How many electrons?

A

3 (6)

6 (12)

45
Q

How many GTP molecules are produced?

A

1 (2)

46
Q

How many electrons where made via 10 x NADH and 2 x FADH2?

A

24 electrons

47
Q

What can the 24 electrons produced by 10 x NADH and 2 x FADH2 be used for?

A

Oxidative phosphorylation

48
Q

What is the catabolic function from the citric acid cycle?

A

Convergent point for carbohydrate, amino acids and fatty acids metabolism

49
Q

What is the anabolic function from the citric acid cycle?

A

Formation of amino acid building blocks and heme
Formation of fatty acids
Forms building blocks of nucleotides
Forms storage products

50
Q

Use this quiz:

A

http://www.purposegames.com/game/0e38fb1b#

BIO1332 - Biochemistry (19 decks)

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