Question

Cyanide, oligomycin, and 2,4-dinitrophenol are all inhibitors of mitochondrial oxidative phosphorylation.

a) Explain why adding cyanide to an active in vitro suspension of mitochondria blocks ATP synthesis.

b) What would happen to the mitochondrial matrix pH when 2,4 dinitrophenol is added to the mitochondrial

suspension following cyanide treatment?

c) Explain what should happen to the rate of ATP synthesis when 2,4 dinitrophenol is added to the

mitochondrial suspension following cyanide treatment.

d) Oligomycin blocks proton translocation by the mitochondrial ATP synthase complex. What should happen

to the rate of oxygen consumption in an in vitro suspension of mitochondria when oligomycin is added.

e) Explain what should happen to the rate of oxygen consumption when 2,4 dinitrophenol is added to the

oligomycin-treated mitochondrial suspension.

Answer 1

a) Cyanide poisons the mitochondrial electron transport chain within cells and renders the body unable to derive energy (adenosine triphosphate—ATP) from oxygen. Specifically, it binds to the a3 portion (complex IV) of cytochrome oxidase and prevents cells from using oxygen, causing rapid death.

c) DNP allows protons to travel down their gradient and back into the mitochondrial matrix without passing through ATP synthase. Thus, it reduces ATP production in cellular respiration. The energy of the gradient is dissipated in the form of heat, raising body temperature.

d) Oxygen consumption stops because oligomycin inhibits ATP synthesis, which is coupled to the activity of the electron-transport chain.