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BIOC192 > Lecture 30: THE FINAL OXIDATION - CITRIC ACID CYCLE > Flashcards

Lecture 30: THE FINAL OXIDATION - CITRIC ACID CYCLE Flashcards

1
Q

Where does the citric acid cycle occur?

A

In the mitochondria (matrix)

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2
Q

Where are the enzymes for the citric acid cycle found?

A

All but one are in the mitochondrial matrix

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3
Q

What is meant by the citric acid cycle being a cycle?

A

It starts and finishes with the same molecule

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4
Q

What does the carbon do in the citric acid cycle?

A

Enters as 2C in Acetyl-CoA and leaves as 2C in 2 CO2 (oxidation complete)

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5
Q

How is energy captured in the citric acid cycle?

A

1 ATP, 3 NADH and 1 FADH2

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6
Q

What are the parts of the citric acid cycle?

A

The first part is release of carbon and the second is regeneration of the molecule

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7
Q

What happens in both parts of the citric acid cycle?

A

Energy is captured

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8
Q

What happens in the condensation of acetly-CoA with oxaloacetate?

A

2C entering the citric acid cycle as acetyl-CoA are attached to 4C oxaloacetate to produce 6C citrate which requires energy

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9
Q

Where does the energy for the condensation of acetly-CoA with oxaloacetate come from?

A

The hydrolysis of CoA from Acetyl-CoA

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10
Q

What is the delta G for condensation of acetly-CoA with oxaloacetate?

A

-32.8 kJ/mol

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11
Q

What happens in the isomerisation of citrate?

A

Rearrangement of citrate to isocitrate (in a dehydration and hydration reaction) makes the molecule susceptible to decarboxylation

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12
Q

What are the steps of isomerisation of citrate catalysed by?

A

Aconitase

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13
Q

What is found in 1080?

A

Fluoroacetate

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14
Q

What happens with fluoroacetate?

A

It is metabolised to fluourocitrate

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15
Q

What is the first part of metabolising fluoroacetate to fluorocitrate?

A

Fluoroacetate + CoA&raquo_space; fluoroacetyl -CoA

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16
Q

What can’t citrate synthase do?

A

Differentiate between fluoroacetly - CoA and acetyl- CoA so converts fluoroacetly - CoA to fluorocitrate

17
Q

What happens with fluorocitrate?

A

It is converted to a substrate that binds tightly to aconitase and inactivates the enzyme, preventing isomerisation

18
Q

What are the consequences of inactivating aconitase?

A

No CAC, an increased concentration of acetyl - CoA so decreased pyruvate dehydrogenase reaction, glycolysis and beta oxidation, also steps downstream of the CAC

19
Q

What type of reaction is the removal of the first carbon?

A

Oxidative decarboxylation which occurs in two steps (oxidation then decarboxylation)

20
Q

Where is energy captured in the removal of the first carbon?

A

In NADH

21
Q

What catalyses the removal of the first carbon?

A

Isocitrate dehydrogenase catalyses both parts

22
Q

What does the intermediate of the removal of the first carbon do?

A

(oxalasuccinate) remains enzyme bound

23
Q

What type of reaction is the removal of the second carbon?

A

An oxidative decarboxylation very similar to the pyruvate dehydrogenase reaction

24
Q

Where is energy captured in the removal of the second carbon?

A

NADH

25
Q

What does the reaction removing the second carbon use?

A

An enzyme requiring lots of cofactors and coenzymes

26
Q

What happens in the removal of the second carbon?

A

Deprotonated carboxyl group is cleaved and the energy is used to add CoA

27
Q

What is the delta G for the removal of the second carbon?

A

-33.4 kJ/mol

28
Q

What happens in the reaction of succinyl-CoA to succinate?

A

The removal of CoA releases enough energy to drive the synthesis of GTP

29
Q

What is GTP?

A

The energy equivalent of ATP (GTP + ADP <> GDP + ATP). There is an increased GTP and ADP (because ATP is being used) which will drive the synthesis of ATP

30
Q

What type of reaction is succinyl-CoA to succinate?

A

A substrate level phosphorylation

31
Q

What happens in a substrate level phosphorylation?

A

The direct use of energy from a substrate molecule to drive the synthesis of ATP (or equivalent). The phosphate does need to come from the substrate (just the energy)

32
Q

What are the reactions used to convert succinate to oxaloacetate similar to?

A

Beta oxydation (oxidation, hydration, oxidation)

33
Q

Where is succinate dehydrogenase found?

A

In the inner mitochondrial membrane

34
Q

What does SDH use as a coenzyme?

A

FAD

35
Q

Where are flavin coenzymes found?

A

Tightly bound to the proteins with which they interact (flavoproteins)

36
Q

What must happen with FADH2?

A

It must be oxidised back to FAD in the electron transport chain which occurs in the inner mitochondrial membrane

37
Q

What is the equation for the SDH reaction?

A

Succinate + E-FAD&raquo_space;> Fumarate + E-FADH2

38
Q

What is the overall reaction for the citric acid cycle?

A

Acetyl - CoA + 3NAD+ + FAD + 2H2O + GDP + Pi&raquo_space;> 2CO2 + CoASH + 3NADH + 3H+ + FADH2 + GTP

39
Q

What is the delta G for the citric acid cycle?

A

-44.3 kJ/mol (energetically favourable)

BIOC192 (38 decks)

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