Final answer:
ATP synthesis will stop in mitochondria when cells are incubated with 2,4-dinitrophenol (DNP), as it disrupts the proton gradient necessary for ATP production, leading to energy being released as heat instead of being stored in ATP. The correct option is A.
Step-by-step explanation:
If you incubate cells with 2,4-dinitrophenol (DNP), a compound that disrupts proton gradients across the inner membrane of mitochondria by acting as an uncoupler, you would predict that ATP synthesis will stop in the mitochondria.
This is due to the fact that DNP transfers protons across the mitochondrial membrane, thereby diverting their flow from ATP synthase (also known as F1F0 ATPase), which is crucial for the synthesis of ATP.
As a result of this uncoupling, the electrochemical gradient necessary for the phosphorylation of ADP to ATP is dissipated, leading to a decrease in ATP production.
With the proton gradient eliminated, the pH across the inner mitochondrial membrane will equalize, disrupting the proton motive force driving ATP synthesis. As a result, even though electrons continue to flow through the electron transport chain, the energy they release is not captured in the form of ATP but instead released as heat.
This increased heat production would lead to higher metabolic rates, which can explain why DNP was considered an effective weight-loss drug; however, its use was discontinued due to the severe risks it poses to human health, including hyperthermia and death. The correct option is A.