Citric Acid Cycle Steps Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

1) Citrate Synthase

A

This catalyses condensation of acetyl-CoA and ocaloacetate, forming citrate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

1) Reactive Pathway of Citrate Synthase

A

O binds, which CC a two-domain cleft containing O binding site, where binding initiates 18 degree rotation, closing cleft, revealing ACOA binding site, and sealing the O one.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

1) Why is it important the Oxaloacetate cleft closes?

A

So solvents cannot reach it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

2) Aconitase

A

Catalyses isomerization of citrate and isocitrate, with a cis-isocitrate intermediate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

2) Reactive pathway of Aconitase

A

A proton/OH group are removed from citrate, where aconitase FE-S cluster facilitatse OH group elmination; cis-Isocitrate is then rehydrated,

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

2) How does aconitase ensure the correct of citrates stereoisomers are formed?

A

Two carboxymethyl groups substituent to its central C, so water can only be eliminated from one of the carboxymethyl arms(the lower one)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Chiral

A

Something asymmetric in such a way that it and its mirror image are NOT superimposable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

2) Why is citrate prochiral?

A

Because although it is achiral(lacking a stereocenter), it can be converted to being chiral (isocitrate)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

2) Why is the prochirality of Citrate important?

A

It allows aconitase to distinguish between the two arms.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Iron-Sulfur Cluster

A

An arrangement of four sulfur and four iron atoms.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

3) NAD+ dependent isocitrate dehydrogenase

A

This catalyses oxidative decarboxylation of isocitrate to a-ketoglutarate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

3) Reaction pathway of ICD?

A

Catalysis of oxidation of isocitrate to an intermediate, oxalosuccinate, followed by decarboxylation to a second intermediate, then formation of a-ketoglutarate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

4) a- Ketoglutarate Dehydrogenase

A

Catalyses oxidative decarboxylation of a-Ketoglutarate, producing second CO2, forming succinyl COA.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

4) What is the reaction pathway of AKGD?

A

It is a ME, with identical reaction pathway to PDC.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

5) Succinyl-CoA thiokinase

A

Couples high-energy S-COA cleavage to synthesis of high-energy NTP, forming succinate.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

5) What are the three steps of Succinyl-CoA thiokinase?

A

Succinyl-CoA reacts with Pi, forming succinyl phosphate and CoA
The phosphate is transferred from succinyl phosphate to a his residue on the thiokinase
Phosphate is transferred to GDP, forming GTP.

17
Q

5) How is energy conserved through Succinyl-CoA thiokinase reaction pathway?

A

Formation of high energy compounds

18
Q

5) What is the culmination of the first 5 steps?

A

One acetyl oxidised to two CO2, with formation of 2 NADH and one GTP

19
Q

6) Succinate Dehydrogenase

A

This causes dehydrogenation of succinate to fumarate

20
Q

What is the only membrane bound CAC enzyme?

A

Succinate Dehydrogenase

21
Q

6) What is succinate dehydrogenase dependent on?

A

Reoxidation of FADH2, as it is dependent on it.

22
Q

6) How does succinate dehydrogenase reoxidise FADH2?

A

Passing its electrons to mitochondrial ETC.

23
Q

7) Fumarase

A

Catalyses hydration of fumarate, forming malate

24
Q

8) Malate Dehydrogenase

A

This regnerates oxaloacetate, oxidising the OH group of malate.

25
Q

8) What is the DeltaG of malate dehydrognease?

A

+29.7kJ

26
Q

8) How is malate dehydrogenase drive forwards, despites its positve DeltaG?

A

The exergonic nature of citrate synthase in the first step,, with a negative -31.5 kJ, due to thioester bond cleavage.

27
Q

What properties are identified to know how a metabolic pathway is controlled?

A

The enzymes catalyzing the rate-determining steps, the effectors of the enzymes and the concentrations of these effecetors.

28
Q

What is required for identifying rate determining steps?

A

Determining DeltaG of each of its reactions from concentration of substrates and prodcuts.

29
Q

Which enzymes regulate CAC?

A

Citrate Synthase, Isocitrate Dehydrogenase and the AKDC

30
Q

What is metabolite flux through the CAC proportional to?

A

O2 consumption

31
Q

How is CAC metabolite flux proportional to O2 consumpton?

A

As in O2 consumption, NADH reoxidation and ATP production are tightly coupled, so CAC regulates based on feedback mechanisms co-ordinating NADH production with energy expenditure.

32
Q

What are CAC enzyme regulation dependent on?

A

Substrate availability
Product inhibition
Competetive feedback inhibtion by intermediates further down the cycle.

33
Q

What are the most critical regulators of the CAC?

A

Acetyl- CoA, Oxaloacetate and NADH.

34
Q

Why is citrate synthase rate variable by substrate concentration?

A

Because ACOA and O are present in the mitochondria in concentratsion that do not saturate CS.

35
Q

What does Oxaloacetate concentration fluctuate with?

A

NADH/NAD+ ratio

36
Q

How does Aconitase distinguish between the two arms of citrate?

A

Its central carbons bound groups are in different dimensions of space, so the central carbons hydroxyl will always be in the same plane as the lower arm.