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Bioc 2580 > The Citric Acid Cycle > Flashcards

The Citric Acid Cycle Flashcards

1
Q

What is the overall purpose of the TCA cycle

A

convert the acetate moieties derived from the catabolism of fats and carbs and turn them into carbon dioxide

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2
Q

The energy released in the TCA is conserved in the form of ____________ _______________

A

reduced cofactors (NADH and FADH2)

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3
Q

What makes the TCA cycle oxygen dependent

A

NADH and FADH2 need to be oxidized back to NAD+ and FAD in the electron transport chain

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4
Q

What did Hans Krebs discover about the TCA cycle that was so important

A

it is cyclic

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5
Q

What is step 1 of the Krebs cycle

A

condensation of acetyl CoA with oxaloacetate to form citrate
*only TCA cycle that forms a C-C bond
- acetyl CoA is bound to oxaloacetate with the addition of water

*results in citrate, and the release of CoASH

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6
Q

What is the final product of step 1 of the TCA cycle, and what enzyme and cofactors were required to obtain it

A

citrate
via citrate synthase
cofactor is H2O - release of CoASH

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7
Q

What is step 2 of the Krebs cycle

A

isomerization of citrate by aconitase
- citrate is converted into isocitrate (isomers of one another) via the removal of water to form cis-aconitate and then addition of water to form isocitrate

results in isocitrate

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8
Q

What enzyme is required in step 2 of TCA cycle

A

aconitase

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9
Q

Citrate is a tertiary alcohol, therefore it is a ________ substrate for oxidation

A

poor substrate
- why it is converted into isocitrate

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10
Q

Isocitrate is a secondary alcohol, therefore it is a ____________ substrate for oxidation

A

good

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11
Q

What is step 3 of the Krebs cycle

A

oxidative decarboxylation of isocitrate (isocitrate dehydrogenase)
- oxidation of alcohol to ketone through the transfer of a hydride

results in a-ketogluterate

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12
Q

What is the enzyme used in step 3 of the TCA cycle and what cofactor is present

A

isocitrate dehydrogenase
NAD+ cofactor - release of NADH

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13
Q

What is step 4 of the Krebs cycle

A

oxidative decarboxylation of a-ketogluterate
- identical to mechanism of pyruvate dehydrogenase complex
- converts a-ketogluterate to high energy thioester succinyl CoA

results in succinyl CoA

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14
Q

What is the enzyme used in step 4 of the TCA cycle an what cofactors are used

A

a-ketogluterate dehydrogenase
NAD+ and CoASH cofactors

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15
Q

What deficiency would lower the efficiency and occurrence of the oxidative decarboxylation of a-ketoglutarate (step 4 of Krebs)

A

thymine

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16
Q

What is step 5 of the Krebs cycle

A

substrate level phosphorylation (succinyl CoA synthetase)
- high energy thioester bond of succinyl CoA is hydrolyzed
*involves formation of phosphoenzyme intermediate

results in succinate

17
Q

What enzyme is used in step 5 of TCA cycle and what cofactor is present

A

succinyl CoA synthetase
GDP + Pi synthesized to GTP as cofactor
(CoASH released)

18
Q

What is step 6 of the Krebs cycle

A

oxidation of succinate to fumarate (succinate dehydrogenase)
- oxidizes succinate to the alkene fumarate
*analogous to the acyl-CoA dehydrogenase reaction of beta oxidation

results in fumarate

19
Q

What enzyme is used in step 6 of the TCA cycle and what cofactor is present

A

succinate dehydrogenase
FAD cofactor

20
Q

What is step 7 of the Krebs cycle

A

hydration of fumarate to malate
- the alkene fumarate is hydrated to the alcohol malate
*analogous to the enoyl-CoA hyratase reaction of beta oxidation

results in malate

21
Q

What enzyme is used in step 7 of the TCA cycle and what cofactor is present

A

fumarase
H2O is added (no real cofactor)

22
Q

What is step 8 of the Krebs cycle

A

oxidation of malate to oxaloacetate
- malate is oxidized to oxaloacetate
*analogous to the hydroxyacyl-CoA dehydrogenase reaction of beta oxidation

results in oxaloacetate

23
Q

What enzyme is used in step 8 of the TCA cycle and what cofactor is present

A

malate dehydrogenase
NAD+ cofactor

24
Q

How many CO2 formed in one round of the TCA cycle (and where do they come from)

A

2 CO2 - come from oxidized acetyl groups of acetyl-CoA

25
Q

How many NADH formed in one round of the TCA cycle

A

3

26
Q

How many FADH2 formed in one round of the TCA cycle

A

1

27
Q

How many GTP formed in one round of the TCA cycle

A

1

Bioc 2580 (16 decks)

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