Lecture 9: TCA Cycle

Question 1

What is the whole point of the TCA cycle?

Answer 1

To generate reduced electron carriers FADH2 and NAD to NADH + H+
CO2 a H2O are the by products

Question 2

What are the 8 steps of the triboxylic acid cycle

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Answer 2

1. Pyruvate (3c) is decarboxylated to acetyl CoA (2c) -release of 1 co2
   - production of 1 NADH + H+
2. Actyl CoA (2C) is combined with oxaloacetate (4c) to produce citrate (6c)
   - requires 1 h2o
3. Citrate is isomerised to isocitrate
4. Isocitrate (6c) is oxidised to a-ketogluterate (5c)
   - release of 1 co2
   - production of 1 NADH + H+
5. A-ketogluterate (5c) is oxidised to succinate (4c)
   - release of 1co2
   - production of 1 NADH + H+
   - production of 1 GTP
6. Succinate is oxidised to fumerate
   - production of 1 FADH2
7. Fumerate is hydrated to malate
   - requires 1 h20
8. Malate is oxidised to oxaloacetate
   - production of 1 NADH + H+
   - oxaloacetate can now combine with acetyl CoA a d the cycle can begin again

Question 3

Outline what happens in phase 2: the electron transport chain and oxidative phosphorylation

Answer 3

The reduced electron acceptors move from the matrix of the mitochondrian to the inner mitochondrial membrane were they feed into the electron transport chain.
Because they have been reduced (means they have accepted some electrons)
Those electrons are then passed to a number of electron acceptors down the chain to oxygen which then reduces the oxygen to water (final step)
As they pass their electrons down this electron chain ATP is produced by oxidative phosphorylation

Question 4

How much ATP do we generate from the complete oxidation of 1 mole of glucose

Answer 4

ATP from glycolysis = 2 ATP
ATP from TCA/ ETC = 2 x 12.5 ATP
G3P shuttle = 3 ATP
Total = 30

Question 5

What happens to the 2 NADH + 2H+ in the cytoplasm as a product of glycolysis
This depends on whether O2 is available.
What happens if it is available?
What happens if its not?

Answer 5

If O2 isn't available: it is recycled
So NADH + H+ back to NAD
If it is available:
Pyruvate enters the TCA cycle
What happens to the NADH + H+?
It is transported from the cytoplasm to a mitochondrion using the glycerol phosphate shuttle

Question 6

What is the glycerol phosphate shuttle?

Answer 6

This process not only re-oxidises cytoplasmic NADH + H+ but it allows glycolysis to continue but produces FADH2 inside the mitochondria. As each mole of glucose produces 2 moles of NADH + H+ in glycolysis, the shuttle gives rise to 2 moles of FADH2 in the mitochondria per mole of glucose. These two moles of FADH2 gives rise to 3 moles ATP/mole of glucose via oxidative phosphorylation.
Total ATP produced in A
=2 + 3 = 5 moles of ATP/mole of glucose

Question 7

What is the overall equation for the complete oxidation of glucose to CO2 and H2O

Answer 7

Glucose + 6O2 + 30 ADP + 30 Pi

= 6CO2 + 36H2O + 30 ATP