Question

What effect would the presence of rotenone have on ATP production? What effect would the presence of your inhibitor have on the amount of NAD+, NADH, pyruvate, and oxygen present in the cell?

If cellular respiration is blocked, can cells switch to a backup method for making ATP?

Answer 1

Rotenone is an insecticide and a pesticide that is used widely to prevent crops from infestation.

It acts as a block to the Electron transport chain (ETC) in the mitochondrial membrane. It prevents the transfer for electrons from the complex 1 to Ubiquinone, which will then be transferring electrons to complex 3 and eventually to complex 4. All of these processes lead to the formation of a proton gradient across the membrane which then powers the ATP synthase to synthesize ATP. Since the process is hampered, the hydrogen gradients aren't created. As a result, ATP synthase isn't active and the cells do not produce ATP.

The complex 1 takes electrons from NADH thereby converting it to NAD+ thus restoring the cellular NAD+ pool. Since complex 1 is inhibited, the high energy electrons from NADH can no longer be utilized. This leads to NADH accumulation and depletion of the NAD+ pool. Thus, the cell undergoes a multiple stress situation. Firstly the ATP production is hampered thereby leading to energy depletion and secondly, the NAD+ pool gets depleted thereby leading to loss of electron carriers. These electron carriers are essential for the glycolytic pathway. The various glycolysis converts the 6 carbon glucose molecule into two 3 carbon pyruvate molecules. In this process, one NADH molecule is produced from NAD+. Subsequently, the depletion of the NAD+ pool and accumulation of acidic byproducts from the TCA cycle would act as feedback inhibition for glycolysis thereby preventing the production of pyruvate.

Also, the oxygen that is taken in by the cell will not be able to capture the electrons and thus superoxide radicals will start forming which will lead to DNA damage.

However, the cell will need ATP and NAD+ pool regeneration. To combat this need, it will become essential to use anaerobic methods. Thus, the superoxide poisoning will be inhibited as ETC will be completely erased from the picture. Additionally, pyruvate can then be converted to either acetic acid or ethanol thus producing small amounts of ATP and conversion of NADH to NAD+. This will restore the NAD+ pool while producing energy that the cell needs.

Thus, the cell would revert to anaerobic metabolism when treated with rotenone before it undergoes apoptosis due to high energy needs and superoxide poisoning.