Question

In normal mitochondria the rate of electron transfer is tightly coupled to the demand for ATP. When the rate of use of ATP is relatively low, the rate of electron transport is low. When demand for ATP increases, electron-transport rate increases. Under these conditions of tight coupling, the number of ATP molecules produced per gram of oxygen consumed when NADH is the electron donor-the P/O ratio is about 2.5-3.0.

Ingestion of uncouplers causes profuse sweating and increase in body temperature. Explain this phenomenon in molecular terms. What happens to the P/O ratio in the presence of uncouplers.

Answer 1

In the presence of uncouplers, as the name suggests, it uncouples electron transport from energy production in the mitochondrion ATP synthase. Under normal conditions with tight coupling, In the mitochondria ATP synthase, as protons passes through the ATP synthase among the concentration gradient from a the intermembrane space into the matrix, energy generated is channeled to the formation of ATP from ADP. However, with uncouplers, the energy generated as protons passes through ATP synthase is not necessarily channeled to the formation of ATP (protons transport is not coupled with ATP synthesis) hence energy is released as heat which results in the increased body temperature and sweating as the body’s response to counter the increased heat produced. The amount of ATP produced per molecule of oxygen is thus reduced as more energy from oxidative phosphorylation is lost as heat rather than channeled to ATP production.