Question

The major electron transport chain complexes of mitochondria that are involved in the generation of Reactive Oxygen Species (ROS) are

• A. Complex I and Complex IV
• B. Complex I and Complex III
• C. Complex II and Complex IV
• D. None of these

Hint:

In mitochondria, \textbf{electron leakage at Complex I and III} is the main source of ROS formation.

Answer 1

The Correct Option is B

Step 1: Reactive Oxygen Species (ROS) such as superoxide anion ($\mathrm{O_2^-}$) are generated due to leakage of electrons from the mitochondrial electron transport chain (ETC).
Step 2: Complex I (NADH dehydrogenase) can leak electrons directly to molecular oxygen, forming superoxide.
Step 3: Complex III (cytochrome bc$_1$ complex) also contributes significantly to ROS generation during the Q-cycle.
Step 4: Complex II contributes very little to ROS generation, and Complex IV efficiently transfers electrons to oxygen to form water, not ROS.
Step 5: Hence, the major complexes involved in ROS generation are Complex I and Complex III.