S6 TCA Cycle And Oxidative Phosphorylation

Question 1

What two reactions start the TCA cycle?

Answer 1

1. Pyruvate (3C) + CoA to Acetyl CoA (2C)+ CO2 (enzyme: pyruvate dehydrogenase)
2. Acetyl CoA (2C) + Oxaloacetate (4C) to Citrate (6C) (oxidation of Acetyl CoA)

Question 2

Is citrate a high or low energy molecule?

Answer 2

High energy - because it’s produced

Question 3

How many NADH, FADH2 and GTP molecules are produced?

Answer 3

6 NADH
2 FADH2
2 GTP

Question 4

What is GTP?

Answer 4

Lower energy equivalent of ATP

Question 5

How is the TCA cycle regulated?

Answer 5

It is regulated by energy availability (presence/ratio of low and high energy molecules).

Stimulated by: ADP and NAD+
Inhibited by: ATP, NADH and succinyl-CoA

Question 6

How are the ETC and ATP synthesis uncoupled?

Answer 6

By uncouplers that increase the permeability of the inner mitochondrial membrane to H+. Means the H+ gradient is reduced (H+ move back through membrane without ATPase) so less/no drive for ATP synthesis.

Question 7

Name two inhibitors of oxidative phosphorylation and how they inhibit.

Answer 7

1. CN-
2. CO

Inhibit by blocking the ETC.
They mimic O2 so bind to Hb inhibiting the O2 to H2O reaction.

Question 8

Coenzymes in oxidative phosphorylation

Answer 8

NADH to NAD+
FADH2 to FAD

Electrons in NADH have more energy than FAD2H

Question 9

What is a PTC?

What is pmf?

Answer 9

Proton translocating complex - “pump” H+ into intermembrane space.

Proton motive force - H+ gradient across inner mitochondrial membrane.

Question 10

Oxidative vs substrate level phosphorylation

Answer 10

Oxidative: requires membrane-associated complexes, indirect energy coupling, can’t occur without O2, major process for ATP synthesis in cells needing lots of energy.

Substrate level: requires soluble enzymes, direct energy coupling, can occur without O2, minor process for ATP synthesis in cells needing lots of energy

Question 11

What is the link between brown adipose tissue and uncoupling of ETC and ATP synthesis?

Answer 11

Brown adipose tissue contains thermogenin (natural uncoupling protein). In response to the cold, noradrenaline activates:

1. Lipase to release fatty acids from triacylglycerol
2. Fatty acid is oxidised, produces NADH/FADH2 which are used in the ETC
3. Fatty acids activate thermogenin
4. Thermogenin transports H+ back into mitochondria (uncoupling) as H+ gradient reduced
5. Energy produced by pmf is released as hea

Question 12

Which 5 biosynthetic processes does the TCA cycle supply?

Answer 12

1. Citrate - Fatty acids
2. Alpha-ketoglutarate - amino acids
3. Succinate - haem and amino acids
4. Malate - amino acids
5. Oxaloacetate - glucose and amino acids

(Amino acid ones are reversible)