Sesh 2- TCA cycle and oxidative phosphorylation

Question 1

Where does the TCA cycle occur?

Answer 1

Mitochondrial matrix

Question 2

Why are there no known genetic defects in the TCA cycle?

Answer 2

They would be lethal, as it is a central pathway of catabolism.

Question 3

Apart from its role in the TCA cycle, what else can citrate be used for?

Answer 3

Fatty acid synthesis

Question 4

What is the role of pyruvate carboxylase?

Answer 4

Converts pyruvate to oxaloacetate

Question 5

Which 2 ratios are used to control the TCA cycle?

Answer 5

• ATP:ADP

- NADH: NAD+

Question 6

What reaction does isocitrate dehydrogenase catalyse?

Answer 6

The irreversible conversion of isocitrate to alpha-ketoglutarate

Question 7

What are the 2 major functions of the TCA cycle?

Answer 7

• Break all C-C bonds in acetyl CoA

- Oxidise C atoms to CO2

Question 8

Which carrier molecule contains the highest energy electrons?

Answer 8

NADH

Question 9

What is the net yield of ATP from one mole of glucose?

Answer 9

32 ATP

Question 10

Where does oxidative phosphorylation occur?

Answer 10

Inner mitochondrial membrane

Question 11

Why can the electron transport chain only occur in the presence of oxygen?

Answer 11

Oxygen is the terminal acceptor of electrons.

Question 12

What is normally the only way that protons can re-enter the mitochondrial matrix?

Answer 12

Via the ATP synthase complex.

Question 13

How is the proton motive force generated?

Answer 13

Electrons are transferred from NADH/FADH2 sequentially to proton translocating complexes, which use this free energy to drive H+ into the intermembrane space.

Question 14

Why does FADH2 yield less ATP compared to NADH?

Answer 14

The electrons in FADH2 contain less energy, so it feeds in to the electron transport chain at proton translocating complex 2 rather than 1.

Question 15

What does the efficiency of ATP synthesis in oxidative phosphorylation depend on?

Answer 15

How impermeable the inner mitochondrial membrane is to H+, as this affects generation of the proton motive force.

Question 16

How does the proton motive force affect the relative production of ATP?

Answer 16

Greater the proton motive force, more ATP produced.

Question 17

What happens to oxidative phosphorylation, and therefore the rest of glucose metabolism when [ATP] is high?

Answer 17

• Means [ADP] is low, so ATP synthase stops working
• Leads to buildup of H+ in inter membrane space, so proton translocating complexes stop
• This prevents re-oxidation of carriers, so negative feedback on prior pathways

Question 18

How does dinitrophenol lower ATP production?

Answer 18

Uncouples electron transport chain from ATP synthesis by increasing inner mitochondrial membrane permeability to H+. Less of a proton motive force is set up and more energy is lost as heat.

Question 19

What is the role of Uncoupling Protein 1 (UCP1)?

Answer 19

Expressed in brown adipose tissue, to uncouple electron transport from ATP synthesis by increasing inner mitochondrial membrane permeability to H+.
More energy lost as heat for non-shivering thermogenesis.

Question 20

How does cyanide inhibits the electron transport chain?

Answer 20

Binds the haem group of the terminal proton translocating complex (cytochrome C oxidase), meaning O2 cannot bind and act as the terminal electron acceptor.

Question 21

Which molecule combines with acetyl CoA to form citrate in the first step of the TCA cycle?

Answer 21

Oxaloacetate

Question 22

Which stage in the metabolism of glucose produces the most ATP?

Answer 22

Electron transport chain