You are carrying out experiments on isolated skeletal muscle mitochondria. For these experiments you are using malate as the oxidizable substrate. Following the addition of malate you add the electron transport inhibitor cyanide. You then examine the oxidation state of various components of the electron transport chain. Which of the following would be expected to be in an oxidized state following this experiment?
A) coenzyme Q
B) complex I
C) complex II
D) complex III
E) cytochrome c

Question

Quizplus · Accepted Answer

Cyanide inhibits the transfer of electrons through complex IV (cytochrome oxidase). In order for any of the components of electron transport to be in an oxidized state they must have either transferred electrons to the next component downstream or never have received electrons in the first place. Oxidation of malate generates NADH which gives its electrons to complex I which then gives the electrons to coenzyme Q which then gives the electrons to complex II, then to cytochrome c, and finally they are passed to complex IV. Since cyanide blocks the transfer of electrons from complex IV to oxygen, all of the upstream electron acceptors will be "blocked" in the reduced state. Only complex II will have never accepted electrons and thus will be in the oxidized state under the conditions of this experiment.

You Are Carrying Out Experiments on Isolated Skeletal Muscle Mitochondria