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BIOCH 200 > Citric Acid Cycle > Flashcards

Citric Acid Cycle Flashcards

1
Q

What is the overall reaction equation of the CAC?

A

Acetyl-CoA + 2H20 + OH –> 2CO2 + Hs-CoA + 7H +8e

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2
Q

Where do 6/8 electrons go?

A

The transfer to 3 molecules of NAD+ with 3 protons.

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3
Q

Where do the remaining 2 electrons go?

A

One molecule Q with two protons.

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4
Q

How many free protons are produced per pyruvate?

A

2.

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5
Q

For each acetyl group that enters the pathway, what are the products?

A

2 CO2
NADH and QH2
GDP
Oxaloacetate

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6
Q

What occurs in the first step of the CAC?

A

Citrate synthesis:

Acetyl CoA reacts with oxaloacetate and water to form citrate, Coenzyme A, and a proton.

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7
Q

Is citrate synthesis reversible?

A

Metabolically no, due to the large free energy released to drive the reaction forward.

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8
Q

What enzyme is involved in citrate synthesis?

A

Citrate synthase.

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9
Q

What is citrate synthase inhibited by?

A

Increased concentrations of citrate (larger than physiologically possible).

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10
Q

What is the rearrangement (2nd) step of the CAC?

A

Conversion of citrate to isocitrate.

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11
Q

Is the second step of CAC reversible?

A

Yes.

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12
Q

What is the third step of the CAC?

A

Dehydrogenation of isocitrate occurs in two parts.

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13
Q

What occurs during the first oxidative decarboxylation step of CAC?

A

Isocitrate is oxidized, one of the hydrogens is transferred to NAD+, and one hydrogen is incorporated into the final product.

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14
Q

What enzyme is activated in the first oxidative decarboxylation step of CAC?

A

Isocitrate dehydrogenase.

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15
Q

Is the first oxidative decarboxylation of isocitrate reversible?

A

No, large negative free energy change.

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16
Q

What occurs during the second oxidative decarboxylation step of CAC?

A

Oxalosuccinate (5C) is decarboxylated to form alpha-ketoglutarate.

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17
Q

What enzyme is activated in the decarboxylation of oxalosuccine?

A

Alpha-ketoglutarate dehydrogenase.

18
Q

Is the decarboxylation of oxalosuccinate reversible?

A

No.

19
Q

What enzyme is alpha-ketoglutarate dehydrogenase similar to?

A

PDH.

20
Q

What occurs following the formation of alpha-ketoglutarate?

A

It is oxidated to succinyl-CoA, producing CO2 and NADH.

21
Q

What occurs following the formation of succinyl-CoA?

A

Succinyl CoA is converted to succinate by succinyl CoA synthase in a reversible reaction that involves the SLP of GDP.

22
Q

What occurs following the formation of succinate?

A

Succinate is oxidized reversibly into fumarate, a reaction catalyzed by succinate dehydrogenase.
Q is reduced to QH2 (integral membrane protein II)
FADH2 produced, then reoxidized when it transfers protons to Q.

23
Q

What is succinate dehydrogenase a part of?

A

Membrane bound enzyme part of complex II.

24
Q

What occurs following the formation of fumarate?

A

Hydration of fumarate to synthesize malate. Reversible reaction.

25
Q

What occurs following the formation of malate?

A

Oxidation of malate to regenerate oxaloacetate and a molecule of NADH.

26
Q

Is the formation of oxaloacetate reversible?

A

Yes.

27
Q

Are there any rate limiting steps in CAC?

A

No because it is cyclical.

28
Q

How is the CAC regulated?

A

Inhibited by NADH/ATP

Activated by Calcium and ADP.

29
Q

What enzymes of the CAC are regulated?

A

The oxidative decarboxylators;
Isocitrate decarboxylase
Alpha-ketoglutarate dehydrogenase

30
Q

What can CAC intermediates be used in? Why is this relevant?

A

Synthesis of amino acids, carbohydrates, fats, etc.

It is amphibolic (catabolic and anabolic)

31
Q

What are anaplerotic reactions?

A

Reactions that replenish intermediates of cyclic metabolite pathways.

32
Q

What reaction is anaplerotic?

A

Pyruvate carboxylase enzyme catalyzes the formation of ozaloacetate.

33
Q

How is pyruvate carboxylase regulated?

A

Activated by Acetyl-CoA

Inhibited by ADP.

34
Q

How many ATP are generated per acetyl-CoA?

A

~10;
7.5/3NADH
1.5/1FADH
1 GTP

35
Q

How many ATP does the complete aerobic oxidation of glucose yield?

A

32 ATP

36
Q

What reactions link the CAC to glycolysis?

A

Pyruvate dehydrogenation

37
Q

What reactions are decarboxylation?

A

Isocitrate to alpha-ketoglutarate
Alpha-ketoglutarate to succinyl CoA
Pyruvate to Acetyl-CoA

38
Q

What are the energy capture steps?

A 
Isocitrate to alpha-ketoglutarate
Alpha-keto glutamate to succinyl CoA
Succinyl CoA to Succinate
Succinate to fumarate
Malate to Oxaloacetate
39
Q

What reactiosn are regulated?

A

Isocitrate to alpha-ketoglutarate
Alpha-keto glutamate to succinyl CoA
PDH

40
Q

How much ATP is produced by the oxidation of one molecule lactate?

A

15 ATP

BIOCH 200 (7 decks)

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