5. Oxidative phosphorylation in mitochondria is often monitored by measuring oxy

Question

5. Oxidative phosphorylation in mitochondria is often monitored by measuring oxygen consumption. When ox. phos. Is proceeding rapidly, the mito. will rapidly consume oxygen. If there phos., only small amounts of oxygen will be used. You are given a suspension of iso0 mitochondria and directed to add the following compounds in the order from a to is little ox. h. With the compound, all of the previously added compounds remain present. Predict the effect of each addition on oxygen consumption by the isolated mitoc hondria. (8 pts) a) Glucose b) ADP+P c) Citrate d) Oligomycin e) Succinate f) 2,4-Dinitrophenol g) Rotenone (inhibits Cmplx l) h) Cyanide

Explanation / Answer

(a) Glucose:- Glucose is a major part of the citric acid cycle, and more the amount of glucose more production of NADH for use in oxidative phosphorylation, hence more oxidative phosphorylation so more consumption of Oxygen.

(b) ADP + Pi: - It is the main ingredient for Complex V for ATP synthesis, hence it will also increase the oxygen consumption, along with the more oxidative phosphorylation.

(c) Citrate: Similar work as Glucose, important constituent of Citric Acid Cycle, it will enhance the oxidative phosphorylation and so the oxygen consumption.

(d) Oligomycin: Its and Antibiotic and is known for the inhibition of ATP synthase by blocking the flow of protons via the Fo subunit. So it will cease the oxidative phosphorylation and consumption of oxygen as well.

(e) Succinate: It is an important part of the citric acid cycle and complex II, where it oxidizes to fumarate and reduces ubiquinone. Enhancing the rate of oxidative phosphorylation and hence Oxygen consumption.

(f) 2,4- Dinitrophenol: It is also the inhibitor of oxidative phosphorylation by carrying protons across a membrane by uncoupling them from ATP synthase. Oxygen consumption gets reduced.

(g) Rotenone: It is a pesticide which inhibits the transfer of electrons from complex I to ubiquinone by blocking the ubiquinone-binding site. It slows down the oxidative phosphorylation and oxygen consumption also.

(h) Cyanide: It is a poison inhibits the oxidative phosphorylation by binding more strongly to the Fe–Cu center in cytochrome c oxidase as compared to Oxygen, hence preventing the reduction of oxygen and its consumption.

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