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2.1 Biochemistry of Metabolism > Sean - TCA Cycle/ Krebs Cycle > Flashcards

Sean - TCA Cycle/ Krebs Cycle Flashcards

1
Q

What does TCA stand for?

A

Tricarboxylic acid cycle

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2
Q

What is the function of the TCA cycle?

A

To produce high energy molecules such as NADH and FADH2 which act as electron carriers in the electron transport chain (ETC)

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3
Q

What happens in the ETC?

A

This is where most of the cell’s ATP is made

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4
Q

Where does the TCA cycle take place?

A

Takes place in the mitochondrion (where oxygen is utilised to generate ATP)

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5
Q

What is the first reaction in the TCA cycle?
(6)

A

Citrate synthesis

The formation of citrate from oxaloacetate and acetyl CoA

Condensation reaction catalysed by citrate synthase

Located in the mitochondria matrix

Essentially irreversible

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6
Q

What is citrate synthesis?

A

Formation of citrate from oxaloacetate and acetyl CoA

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7
Q

Where does citrate synthesis take place?

A

The mitochondria matrix

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8
Q

What enzyme catalyses citrate synthesis?

A

Citrate synthase

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9
Q

What happens in the second step of the TCA cycle?
(5)

A

Isocitrate synthesis

Reversible reaction

Two step reaction catalysed by aconitase

First step
- citrate is converted to aconitate via dehydration

Second Step
- aconitate is converted to isocitrate via hydration

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10
Q

The isocitrate synthesis reaction is reversible, which direction is favoured and why?
(2)

A

Forward reaction is favoured (citrate to isocitrate)

This is because isocitrate is quickly used up by step three of the TCA cycle

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11
Q

What enzyme catalyses isocitrate synthesis?

A

Aconitase

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12
Q

What happens in step three of the TCA cycle?
(6))

A

Alpha-ketoglutarate synthesis

Catalysed by isocitrate dehydrogenase

2 step reaction with oxalosuccinate as an intermediate

Isocitrate is oxidatively decarboxylated to oxalosuccinate

Hydrogens are given to NAD+ or NADP+

Oxalosuccinate is then converted into a-ketoglutarate

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13
Q

What catalyses a-ketoglutarate synthesis?

A

Catalysed by isocitrate dehydrogenase

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14
Q

What is the intermediate in a-ketoglutarate synthesis?

A

Oxalosuccinate

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15
Q

What happens in reaction 4 of the TCA cycle?
(4)

A

Synthesis of Succinyl-CoA

Oxidation causes a-ketoglutarate to bind with acetyl-CoA to form succinyl-CoA

Hydrogens are donated to NAD+ to form NADH + H+

Catalysed by a-ketoglutarate dehydrogenase complex

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16
Q

What catalyses succinyl-CoA synthesis?

A

a-ketoglutarate dehydrogenase complex

17
Q

What must bind to a-ketoglutarate to form succinyl-CoA

A

Acetyl CoA

18
Q

What happens in reaction 5 of the TCA cycle?
(5)

A

Succinate synthesis

Succinyl-CoA is converted to succinate

Cleavage of thioester bond releases energy to drive ATP/GTP synthesis

Coenzyme A is released

Catalysed by succinyl-CoA synthetase

19
Q

What catalyses succinate synthesis?

A

Succinyl-CoA synthetase

20
Q

What must be done to succinyl-CoA to form succinate?

A

Succinyl-CoA loses it’s CoA and it’s thioester bond is broken

21
Q

How many types of succinyl-CoA synthetase exist?

A

Two types exist
- one for ADP
- one for GDP

22
Q

How can GTP help out ADP?

A

GTP can donate its terminal phosphoryl group to ADP so it can form ATP

23
Q

What occurs in reaction 6 of the TCA cycle?
(5)

A

Fumarate synthesis

Succinate is converted into succinate

This is catalysed by succinate dehydrogenase

FAD is converted into FADH2

FADH2 produced carries electrons to the ETC to produce ATP

24
Q

What catalyses fumarate synthesis?

A

Succinate dehydrogenase

25
Q

What is the energy carrier in fumarate synthesis?

A

FAD is reduced to FADH2

26
Q

What happens in reaction 7 of the TCA cycle?
(5)

A

Malate synthesis

Fumarate is converted into malate

Catalysed by fumarase

Reversible reaction

Hydration reaction

27
Q

What catalyses the conversion of fumarate into malate?

A

Fumarase

28
Q

What type of reaction is malate synthesis?

A

Hydration reaction

29
Q

What happens in reaction 8 of the TCA cycle?
(4)

A

Oxaloacetate synthesis

Malate is oxidised into oxaloacetate

Catalysed by L-Malate dehydrogenase

Reversible reaction

30
Q

What catalyses oxaloacetate synthesis?

A

L-Malate dehydrogenase

31
Q

How many reactions are in the TCA cycle?

A

Eight

32
Q

List the different molecules in the TCA cycle, in order

A

Oxaloacetate + Acetyl CoA

Citrate

Aconitate

Isocitrate

a-Ketoglutarate

Succinyl-CoA

Succinate

Fumarate

Malate

Oxaloacetate (2)

2.1 Biochemistry of Metabolism (21 decks)

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