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BIO1332 Biochemistry > Citric Acid Cycle > Flashcards

Citric Acid Cycle Flashcards

1
Q

Where does the citric acid cycle take place?

A

mitochondrial matrix.

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2
Q

Give the Link Reaction.

A

Pyruvate > Acetyl CoA by pyruvate dehydrogenase.

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3
Q

Why is the complex structure of pyruvate dehydrogenase useful?

A

Physical proximity of all 3 enzymes in the complex prevents the release of intermediates.
Each enzyme catalyses part of the conversion of pyruvate to Acetyl CoA.
Also contains coenzymes & regulatory molecules.

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4
Q

Pyruvate + CoA + NAD+ >

A

> acetyl CoA + CO2 + NADH

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5
Q

How many steps are in the citric acid cycle?

A

8

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6
Q

Give the 1st step of the citric acid cycle.

A

oxaloacetate + acetyl CoA = citrate
4C 2C 6C
Catalysed by citrate synthase, CoA regenerated & released.

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7
Q

Give the 2nd step of the citric acid cycle.

A

Isomerisation
Citrate > Isocitrate
Catalysed by aconitase.

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8
Q

Explain the 2nd step of the citric acid cycle.

A

Water is removed in the first reaction.
It is added back in in the second reaction, except the position of the OH & H groups have swapped.
Aconitase is an iron-sulphur protein, the iron bind sthe citrate & facilitates the dehydration/hydration reactions.

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9
Q

Give the 3rd step of the citric acid cycle.

A

Oxidation & decarboxylation
Isocitrate > Oxalosuccinate > a-Ketoglutarate
6C 6C 5C
Catalysed by isocitrate dehydrogenase
1st production of NADH + H+
H+ used to release 1st CO2 in 2nd reaction

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10
Q

How is the 3rd step of the citric acid cycle controlled?

A

Allosterically activated by ADP & inhibited by ATP

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11
Q

Give the 4th step of the citric acid cycle.

A 
Oxidation & decarboxylation
a-Ketoglutarate > succinyl CoA
5C                         4C
Catalysed by a-Ketoglutarate dehydrogenase complex
2nd production of NADH + H+
2nd release of CO2
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12
Q

Give the 5th step of the citric acid cycle.

A

Cleavage
Succinyl CoA > succinate
4C 4C
Catalysed by succinyl CoA synthetase

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13
Q

Give the 6th step of the citric acid cycle.

A 
Oxidation
Succinate > fumarate
4C                4C
Catalysed by succinate dehydrogenase
2e- & 2H+ transferred to FAD to make FADH2
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14
Q

Give the 7th step of the citric acid cycle.

A

Hydration
Fumarate > malate
4C 4C
Catalysed by fumarase, requires H20

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15
Q

Give the 8th step of the citric acid cycle.

A 
Oxidation
Malate > oxaloacetate
4C           4C
Catalysed by malate dehydrogenase
3rd production of NADH + H+
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16
Q

What is the importance of the 5th step of the citric acid cycle?

A

Release of CoA from succinyl CoA is coupled to the phosphorylation of GDP to GTP leading to the phosphorylation of ADP to ATP.

17
Q

How is the citric acid cycle regulated in the cell?

A

Negatively by [ATP] & [NADH]

Positively by [ADP]

18
Q

What are the control points in the citric acid cycle?

A

the enzymes:
pyruvate dehydrogenase
isocitrate dehydrogenase
a-Ketoglutarate dehydrogenase

19
Q

Give other inhibitors of the citric acid cycle.

A

Arsenic & Mercury inactivate a component of pyruvate dehydrogenase.
Sodium fluoroacetate combines with CoA & causes irreversible inhibition of aconitase.

20
Q

How many carbons enter & leave the cycle?

A

2 enter

2 leave

21
Q

How many FADH2 molecules are produced per cycle?

A

1

22
Q

How many NADH molecules are produced per cycle?

A

3

23
Q

How many GTP molecules are produced per cycle?

A

1

24
Q

Input of glycolysis.

A

Glucose
2 ADP
2 NAD+

25
Q

Input of pyruvate oxidation.

A

2 pyruvate
2 CoA
2 NAD+

26
Q

Input of citric acid cycle.

A

2 Acetyl CoA
6 NAD+
2 FAD
2 ADP

27
Q

Output of glycolysis.

A

2 pyruvate
2 ATP
2 NADH + H+

28
Q

Output of citric acid cycle.

A 
4 CO2
2 CoA
6 NADH + H+
2 FADH2
2 GTP > 2 ATP
29
Q

Output of pyruvate oxidation.

A

2 Acetyl CoA
2 CO2
2 NADH + H+

30
Q

Catabolic function of the citric acid cycle.

A

Convergent point for carbohydrate, amino acid & fatty acid metabolism.

31
Q

Anabolic function of the citric acid cycle.

A

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

BIO1332 Biochemistry (12 decks)

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