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
What is the energy carrier in fumarate synthesis?
FAD is reduced to FADH2
26
What happens in reaction 7 of the TCA cycle? (5)
Malate synthesis Fumarate is converted into malate Catalysed by fumarase Reversible reaction Hydration reaction
27
What catalyses the conversion of fumarate into malate?
Fumarase
28
What type of reaction is malate synthesis?
Hydration reaction
29
What happens in reaction 8 of the TCA cycle? (4)
Oxaloacetate synthesis Malate is oxidised into oxaloacetate Catalysed by L-Malate dehydrogenase Reversible reaction
30
What catalyses oxaloacetate synthesis?
L-Malate dehydrogenase
31
How many reactions are in the TCA cycle?
Eight
32
List the different molecules in the TCA cycle, in order
Oxaloacetate + Acetyl CoA Citrate Aconitate Isocitrate a-Ketoglutarate Succinyl-CoA Succinate Fumarate Malate Oxaloacetate (2)