Citric Acid Cycle

Question 1

What is another name for citric acid cycle?

Answer 1

Krebs cycle or tricarboxylic acid (TCA)

Question 2

What does the citric acid cycle lead to?

Answer 2

Oxidative phosphorylation

Question 3

Where is the citric acid cycle carried out?

Answer 3

Mitochondrial matrix

Question 4

Where is glycolysis carried out?

Answer 4

In cytoplasm

Question 5

What does pyruvate dehydrogenase complex do?

Answer 5

Pyruvate is converted to Acetyl CoA by

pyruvate dehydrogenase

Question 6

What is pyruvate dehydrogenase complex ?

Answer 6

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

Question 7

What is pyruvate dehydrogenase complex molecular mass?

Answer 7

4 – 10 million daltons

Question 8

How can you view pyruvate dehydrogenase complex ?

Answer 8

Under an electron microscopy

Question 9

Why is Pyruvate dehydrogenase complex

a complex?

Answer 9

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

Question 10

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

Answer 10

E1 E2 E3

Question 11

What is E1?

Answer 11

Pyruvate dehydrogenase

Question 12

What reaction does E1 catalyse?

Answer 12

Oxidative decarboxylation of pyruvate

Question 13

What is the Cofactor of E1?

Answer 13

Thiamine pyrophosphate

Question 14

What is E2?

Answer 14

Dihydrolipoyl transacetylase

Question 15

What is E3?

Answer 15

Dihydrolipoyl dehydrogenase

Question 16

What reaction does E2 catalyse?

Answer 16

Transfer of the acetyl group to CoA

Question 17

What reaction does E3 catalyse?

Answer 17

Regeneration of the oxidised form of lipoic acid

Question 18

What is the cofactor of E2?

Answer 18

Lipoic acid

Coenzyme A

Question 19

What is the cofactor of E3?

Answer 19

FAD

NAD+

Question 20

Pyruvate + CoA + NAD+ produces…

Answer 20

acetyl CoA + CO2 + NADH

Question 21

What is the citric cycle about?

Answer 21

Not proaction of ATP

But removal of electrons and reducing of NADH

Question 22

How many steps are there in the citric acid cycle?

Answer 22

8

Question 23

What is the first step of the citric acid cycle?

Answer 23

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)

Question 24

What is the second step of the citric acid cycle?

Answer 24

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

Question 25

What is the third step of the citric acid cycle?

Answer 25

3: Oxidation and decarboxylation of isocitrate Isocitrate is oxidised and decarboxylated by isocitrate dehydrogenase in a two step process

Question 26

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

Answer 26

Allosterically activated by ADP and inhibited by ATP

Question 27

What is the fourth step of the citric acid cycle?

Answer 27

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

Question 28

What is the fifth step of the citric acid cycle?

Answer 28

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

Question 29

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

Answer 29

Stage 5

Question 30

What is the sixth step of the citric acid cycle?

Answer 30

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

Question 31

What is the seventh step of the citric acid cycle?

Answer 31

7: Hydration of fumarate Fumarate is hydrated to malate by fumarase The reaction requires the addition of H2O

Question 32

What is the eighth step of the citric acid cycle?

Answer 32

8: Oxidation of malate Malate is oxidised to oxaloacetate by malate dehydrogenase Third (and final) production of NADH + H+

Question 33

How is the Krebs cycle negatively regulated?

Answer 33

By the concentrations of ATP and NADH

Question 34

How is the kerbs cycle positively regulated?

Answer 34

By the concentration of ADP

Question 35

What are control points?

Answer 35

Enzymes

Question 36

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

Answer 36

Pyruvate dehydrogenase Isocitrate dehydrogenase a-Ketoglutarate dehydrogenase

Question 37

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

Answer 37

inhibited by ATP, succinyl CoA and NADH

Question 38

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

Answer 38

inhibited by ATP and NADH

Question 39

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

Answer 39

Irreversible reaction. | Inhibited by ATP, acetyl CoA and NADH.

Question 40

How do arsensic and mercury regulate the citric acid cycle?

Answer 40

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

Question 41

How many carbons enter the citric acid cycle?

Answer 41

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

Question 42

How many carbons leave the citric acid cycle?

Answer 42

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

Question 43

How many FADH2 molecules produced? How many electrons?

Answer 43

1 (2) | 2 (4)

Question 44

How many NADH molecules produced? | How many electrons?

Answer 44

3 (6) | 6 (12)

Question 45

How many GTP molecules are produced?

Answer 45

1 (2)

Question 46

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

Answer 46

24 electrons

Question 47

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

Answer 47

Oxidative phosphorylation

Question 48

What is the catabolic function from the citric acid cycle?

Answer 48

Convergent point for carbohydrate, amino acids and fatty acids metabolism

Question 49

What is the anabolic function from the citric acid cycle?

Answer 49

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

Question 50

Use this quiz:

Answer 50

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