ETC Inhibitors

Question 1

What are the major complexes of the Electron Transport Chain?

Answer 1

Complex I – NADH dehydrogenase
Complex II – Succinate dehydrogenase
Complex III – Cytochrome bc1
Complex IV – Cytochrome c oxidase
Complex V – ATP synthase

Each complex plays a critical role in the process of oxidative phosphorylation.

Question 2

Which inhibitor blocks Complex I (NADH dehydrogenase)?

Answer 2

Rotenone (pesticide)
Barbiturates (e.g., amobarbital)
Prevents transfer of electrons from NADH to CoQ

These inhibitors can lead to impaired cellular respiration.

Question 3

Which inhibitor blocks Complex II (Succinate dehydrogenase)?

Answer 3

Thenoyltrifluoroacetone (TTFA)
Malonate (competitive inhibitor of succinate)

Inhibition of this complex affects the Krebs cycle as well.

Question 4

Which inhibitor blocks Complex III (Cytochrome bc1)?

Answer 4

Antimycin A
Blocks transfer from CoQ to cytochrome c

This blockage prevents effective electron transport.

Question 5

Which inhibitor blocks Complex IV (Cytochrome c oxidase)?

Answer 5

Cyanide (CN⁻)
Carbon monoxide (CO)
Hydrogen sulfide (H₂S)
Prevents oxygen from acting as the final electron acceptor

These inhibitors can lead to cellular asphyxiation.

Question 6

Which inhibitor blocks ATP synthase (Complex V)?

Answer 6

Oligomycin
Directly inhibits proton flow through ATP synthase → ↓ ATP production

This action disrupts ATP synthesis despite ongoing electron transport.

Question 7

What is an uncoupler in the ETC? Give examples.

Answer 7

Disrupts proton gradient → electron transport continues but ATP synthesis stops
Examples:
* 2,4-Dinitrophenol (DNP)
* Thermogenin (in brown fat)
* Aspirin (high doses)

Uncouplers can cause increased heat production in the body.

Question 8

What is the effect of uncouplers on oxygen consumption and ATP synthesis?

Answer 8

⬆️ Oxygen consumption
⬇️ ATP synthesis

The increased oxygen consumption is a result of the cells trying to compensate for the lack of ATP production.