Based on the above mechanism of action of cyanide and what you know about the ro

Question

Based on the above mechanism of action of cyanide and what you know about the role of oxygen in aerobic cellular respiration, predict what you would expect if you conducted an experiment in which you examined the effect of cyanide on oxygen consumption. Would oxygen consumption increase, decrease slightly, or be completed halted?What would happen to ATP production: would ATP produced by chemiosmosis increase or decrease, would it eventually halt? Explain

2. Now, comment on whether the effect of cyanide on cellular respiration can be bypassed. Based on what you learned about oxidative phosphorylation in your lecture textbook and during this laboratory, can you bypass the effect of cyanide (which you determined under question 1) by increasing the amount of any substrate of cellular respiration? Explain

3. Next, consider the following experiment:

You isolate whole mitochondria with cristae from cells. In the presence of cyanide, you first place these mitochondria into a slightly acidic solution, and then you transfer them into an alkaline solution. You subsequently observe production of small amounts of ATP.

Explain why the change in pH of the environment resulted in the production of small amounts of ATP by oxidative phosphorylation and thereby temporarily bypassed the effects of cyanide (hint: think about the flow of hydrogen ions across mitochondrial cristae).

4. Finally, consider the following experiment:

You repeat the experiment under question 3. Except now, you also add oligomycin to your reaction flask. After you change the pH of the environment, you no longer observe production of ATP.

Mechanism of action of oligomycin:

Like cyanide, oligomycin is an oxidative phosphorylation inhibitor – except that it acts on a different step of oxidative phosphorylation. Oligomycin specifically binds to an F0 protein of the F 0 F 1 complex (also called the ATP synthase), and thereby inhibits the flow of hydrogen ions through this pump.

Based on the mechanism of action of oligomycin and on the role of ATP synthase in chemiosmosis which you learned about in Biol 211G, explain why in this last experiment you did not observe a small increase in ATP.

Explanation / Answer

In aerobic respiration, electron transport chain is the final process in which the first molecule of ETC accept protons and electrons from Krebs cycle. The electrons are passed from first to last molecule embedded in the mitochondrial membrane. In the last stage, electrons react with oxygen and proton to form water.

Cyanide inhibits the last molecule (cytochrome oxidase a3) so that oxygen cannot bind to it, so oxygen consumption is completely stopped even though oxygen is present, it cannot be consumed. And also ATP production is stopped which is coupled with ETC. Finally total cellular respiration halts

2) Cyanide acts as a competitive inhibitor with high affinity for metals and in cytochrome oxidase it binds to iron. Oxygen level can be increased to reverse the binding of cyanide or with any specific substrate.

3) Binding of cyanide to the cytochrome oxidase is pH dependent. When pH is increased or decreased it directly affects it binding. So ATP is produced.

4) Oligomycin is an antibiotic which binds to ATP synthase to inhibit ATP production. Binding of oligomycin to ATP synthase is pH independent. So increase or decrease in pH has no effect to its binding. So ATP is not produced.

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