USA Biology Olympiad (USABO) Practice Exam

Which compound acts as an uncoupler of electron transport and ATP synthesis in mitochondria?

1. Adenosine triphosphate

2. Dinitrophenol

3. The F0 base piece of ATP synthase

4. B and C only

The correct answer is: B and C only

The compound that acts as an uncoupler of electron transport and ATP synthesis in mitochondria is dinitrophenol. Dinitrophenol disrupts the proton gradient that is essential for ATP production. Normally, during cellular respiration, electrons are transferred through the electron transport chain, resulting in the pumping of protons across the inner mitochondrial membrane. This establishes a proton gradient that ATP synthase uses to produce ATP. Dinitrophenol, by allowing protons to leak back into the mitochondrial matrix, uncouples this process, leading to a decrease in ATP synthesis despite continued electron transport. While the F0 base piece of ATP synthase is essential for ATP synthesis, it does not itself act as an uncoupler; rather, it is the mechanism through which the proton gradient is harnessed to produce ATP. Thus, only dinitrophenol serves as an uncoupler in this context. Therefore, while option D includes both dinitrophenol and the F0 base piece, only dinitrophenol is directly responsible for uncoupling electron transport from ATP synthesis. Hence, it is important to identify the primary uncoupling agent clearly when considering the role of various compounds in mitochondrial physiology.