L14: The TCA Cycle

Question 1

TCA Cycle
1. Definition
2. Location
3. Tissues
4. Functions

Answer 1

1. Oxidation of acetyl CoA to CO2 & Water
2. Mitochondrial Matrix
3. All tissues with mitochondria
4. Energy trapping

Question 2

What bond is formed between CoA & carboxylic acids?

Answer 2

Thioester bonds

Question 3

Define decarboxylation

Answer 3

Removal of C

Question 4

What is the conversion of pyruvate to acetyl CoA catalysed by?

Answer 4

Pyruvate dehydrogenase

Question 5

Equation for conversion of pyruvate to acetyl CoA

Answer 5

Pyruvate + CoA + NAD+ -> AcetylCoA + CO2 + NADH+H+

Question 6

Why is the conversion of pyruvate to acetyl CoA reaction irreversible & can’t generate free glucose from fatty acids?

Answer 6

Can’t go back from acetyl coA to pyruvate

Question 7

1st step of TCA cycle

Describe condensation reaction of the TCA cycle

Answer 7

4C oxaloacetate combines with 2C acetyl CoA which is catalysed by **citrate synthase **to produce 6C citrate

Question 8

2nd step of TCA cycle

Describe isomerisation stage of the TCA cycle

Answer 8

6C citrate is catalysed by aconitase to produce 6C isocitrate

Question 9

3rd step of TCA cycle

Describe the first loss of CO2 stage of the TCA cycle

Answer 9

6C isocitrate is catalysed by** isocitrate dehydrogenase**, 2H+ are lost & CO2 is lost to produce a-ketoglutarate

Question 10

4th step of TCA cycle

Describe the 2nd loss of CO2 stage in the TCA cycle

Answer 10

a-ketoglutarate is catalysed by a-ketoglutarate dehydrogenase to produce succinyl CoA. 2H+ & CO2 is lost.

Question 11

If acetyl CoA has 2C, but 4C has been lost in previous decarboxylation reactions, why does the cycle continue?

Answer 11

Oxaloacetate is re-generated to get more high energy intermediates (NADH & FADH2)

Question 12

5th step of TCA Cycle

Describe the trapping thioester bond energy as GTP stage in the TCA cycle

Answer 12

Succinyl CoA is catalysed by succinyl-CoA synthetase to produce succinate. GTP is phosphorylated by GDP + Pi & CoA is released.

Question 13

6th step of TCA cycle

Describe the conversion of succinate to fumarate stage in the TCA cycle

Answer 13

Succinate is catalysed by succinate dehydrogenase to produce fumarate. FADH2 is produced.

Question 14

7th step of TCA cycle

Describe conversion of fumarate to malate stage in the TCA cycle

Answer 14

Fumarate is catalysed by **fumarase **to produce malate. H2O is added.

Question 15

8th step of TCA cycle

Describe the conversion of malate to oxaloacetate stage in the TCA cycle

Answer 15

Malate is catalysed by malate dehydrogenase to produce oxaloacetate. NADH is produced and OAA is reformed.