Uncoupler 2, 4-Dinitrophenol and its effect on mitochondria

The addition of the uncoupler 2, 4-Dinitrophenol (DNP) to actively respiring mitochondria causes a decrease in ATP production and an increased rate of O2 consumption. Let's explore the reasons behind this phenomenon in detail.

Introduction to mitochondrial respiration and ATP production

Mitochondria are known as the powerhouses of the cell because they play a crucial role in generating ATP (adenosine triphosphate), which is the primary energy currency of cells. ATP is produced through a process called oxidative phosphorylation, which occurs in the inner mitochondrial membrane.

During oxidative phosphorylation, electrons from NADH and FADH2 (generated in previous stages of cellular respiration) are transported along the electron transport chain (ETC) embedded in the inner membrane. As electrons move through the ETC, protons (H+) are pumped from the matrix to the intermembrane space, creating an electrochemical gradient.

This proton gradient is then utilized by ATP synthase, a complex enzyme, to generate ATP from ADP and inorganic phosphate (Pi). This process is known as chemiosmosis, where ATP synthase couples the flow of protons down their electrochemical gradient to the synthesis of ATP.

Understanding the role of 2, 4-Dinitrophenol (DNP)

2, 4-Dinitrophenol (DNP) is an uncoupling agent that disrupts the chemiosmotic mechanism of ATP synthesis in mitochondria. It acts by dissipating the proton gradient across the inner mitochondrial membrane, uncoupling the flow of protons from ATP synthesis.

Effect of DNP on ATP production

When DNP is added to actively respiring mitochondria, it acts as a protonophore, meaning it facilitates the movement of protons across the inner mitochondrial membrane. This movement of protons bypasses ATP synthase and leads to the dissipation of the proton gradient.

As a result, the chemiosmotic coupling between electron transport and ATP synthesis is disrupted. This uncoupling effect prevents ATP synthesis and decreases the overall production of ATP. Hence, option 'A' is the correct answer.

Effect of DNP on O2 consumption

Since DNP uncouples the electron transport chain from ATP synthesis, the energy that would have been used to generate ATP is instead dissipated as heat. This increase in energy dissipation leads to an increased rate of O2 consumption by the mitochondria.

Oxygen consumption is directly linked to the electron transport chain and ATP synthesis. When DNP is added, the electron transport chain continues to operate, but the energy released from electron transfer is not utilized for ATP production. As a result, the excess energy is converted into heat, and more oxygen is consumed in the process.

Conclusion

The addition of the uncoupler 2, 4-Dinitrophenol (DNP) to actively respiring mitochondria causes a decrease in ATP production due to the disruption of the chemiosmotic coupling between electron transport and ATP synthesis. This uncoupling effect also leads to an increased rate of O2 consumption as the excess energy is dissipated as heat.