3. Tricarboxylic Acid Cycle

Question 1

What do Monocarboxylate Transporters (MCTs) do?

Answer 1

facilitate transport of lactate + pyruvate into the mitochondria
There isoforms are MCT1 to MCT7
MCT1 and MCT4 are abundant in the muscle

Question 2

what does the pyruvate dehydrogenase complex do?

Answer 2

breaks down pyruvate into acetyl-CoA to go into the TCA cycle

It is a redox reaction

Question 3

What happens in the TCA cycle?

Answer 3

1. Oxaloacetate + acetyl-CoA to make a 6C citrate. Enzyme = citrate synthase
2. citrate –> isocitrate. Enzyme = aconitase
3. Co2 molecule breaks off isocitrate to form alpha-ketoglutarate. NADH molecule made. Enzyme=isocitrate dehydrogenase
4. a-ketoglutarate to succinyl-CoA from CO2 splitting off and NADH being formed. Enzyme = a-ketoglutarate dehydrogenase.
5. succinyl-CoA –> succinate. The CoA is split off. Enzyme = succinyl-CoA synthase.
6. succinate –> fumerate. Oxidised. Enzyme = succinate dehydrogenase.
   FAD also becomes FADH2 here
7. fumerate –> L-malate. Oxygen is added. Enzyme = fumerase.
8. L-malate –> oxaloacetate. Enzyme = malate dehydrogenase

Question 4

What are the 3 ways in which the TCA cycle can be regulated?

Answer 4

1. Substrate availability - eg if there isnt enough citrate then that leads to more oxaloacetate. Too much and then there is more citrate synthase.
2. Product inhibition - a high level of product will inhibit the enzyme that makes it .
3. Allosteric Regulation - how things like ATP ADP etc inhibit or stimulate the 3 key enzymes –> (citrate synthase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase)

Question 5

What is anaplerosis?

Answer 5

a series of enzymatic reactions that replenish the TCA - cycle intermediates

Question 6

What is cataplerosis?

Answer 6

A series of enzymatic reactions that remove TCA-cycle intermediates