Question

Cyanide and carbon monoxide block the final step in the electron transport chain. What effect would this have on ATP production in the mitochondria? (Pick only one)

ATP production would increase, because this would spontaneously establish a stronger proton gradient.

ATP production would not change, because protons cross the outer mitochondrial membrane to produce ATP.

ATP production would decrease, because protons would not be able to move across the inner mitochondrial membrane.

ATP production would decrease, because electrons would not move through the electron transport chain and reduce oxygen.

ATP production would increase, because this would make more oxygen available in the mitochondrial matrix.

Answer 1

ATP production would decrease, because electrons would not move through the electron transport chain and reduce oxygen.

Cyanide binds to cytochrome c oxidase (especially the Fe3+ ion) and hinders the electron flow from it to the final electron acceptor, the oxygen. This causes loss of reduction of oxygen into water. As the electron flow is inhibited, ATP production would automatically decrease due to less proton gradient in the intermembrane space.

ATP production would increase, because this would spontaneously establish a stronger proton gradient.

This is wrong. ATP production wouldn’t increase, because cyanide poisoning would reduce proton gradient.

ATP production would not change, because protons cross the outer mitochondrial membrane to produce ATP.

This is wrong. ATP production would decrease, as the proton pumping across the inner membrane (not the outer membrane) is reduced due to cyanide poisoning.

ATP production would decrease, because protons would not be able to move across the inner mitochondrial membrane.

This is wrong. Cyanide poisoning would reduce the proton pumping across the membrane not completely halt it.

ATP production would increase, because this would make more oxygen available in the mitochondrial matrix.

This is wrong. Cyanide poisoning would not increase ATP production by making more oxygen available in the matrix. In fact, these oxygen molecules are easily convertible to oxygen free radicals which would damage the mitochondria.