Question

What effect does the addition of 2,4-dinitrophenol, a proton carrier, have on mitochondria in which ATP synthesis is inhibited by oligomycin?

A) Inhibits electron transport
B) Stimulates ATP synthesis
C) Restarts electron transport
D) Increases oligomycin effectiveness

Answer 1

2,4-dinitrophenol (DNP) stimulates ATP synthesis by uncoupling oxidative phosphorylation, restoring proton flow and bypassing ATP synthase, which oligomycin inhibits.

Step-by-step explanation:

The addition of 2,4-dinitrophenol (DNP), a proton carrier, to mitochondria with ATP synthesis inhibited by oligomycin results in stimulation of ATP synthesis (B). Oligomycin works by inhibiting the F0F1ATPase (ATP synthase), effectively stopping ATP production while the electron transport chain (ETC) is still functional. DNP acts as an uncoupler by making the inner mitochondrial membrane leaky to protons, thus dissipating the proton gradient. Despite the presence of oligomycin, DNP allows for the restoration of the proton flow across the mitochondrial membrane but bypasses ATP synthase. Because the ETC continues to operate to maintain the electrochemical gradient, a byproduct of this uncoupled function is heat production, making DNP an effective yet dangerous weight loss drug in the past due to the risk of hyperthermia.