BIOCHEM The figure below shows the oxygen consumption in mum

BIOCHEM

The figure below shows the oxygen consumption, in mumol, of intact mitochondria upon addition of various agents. For the following agents, explain the chemical nature of the agent, and why the change in O_2 consumption is observed. a. Citrate b. Oligomycin c. Dinitrophenol d. Cyanide From the data, determine the mumols of ATP generated upon addition of the excess ADP

Solution

Answer:

6. a. Citrate:

Citric acid is a weak organic tricarboxylic acid having the chemical formula C₆H₈O₇ and is an intermediate in the citric acid cycle.

The [O₂] falls because citrate is a fuel and ATP can be formed from ADP and P_i.

b. Oligomycin:

Oligomycins are macrolides created by Streptomyces that can be poisonous to other organisms. It acts as an inhibitor of ATP synthase by blocking its proton channel.

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

c. Dinitrophenol:

The compound 2,4-dinitrophenol (DNP) acts as a proton ionophore, that is, it binds protons on one side of a membrane, and being fat-soluble it drifts to the opposite side where it loses the protons.

[O₂] falls rapidly because the system is uncoupled and does not require ATP synthesis to lower the proton-motive force.

d. Cyanide:

Cyanide binds to the ferric form of cytochrome oxidase and thereby inhibits oxidative phosphorylation.

Oxygen consumption ceases because Complex IV is inhibited and the entire chain backs up.