Which complex in mitochondrial ETC does not pump out H ions ?
**Core Concept**
Mitochondrial Electron Transport Chain (ETC) is a crucial process for generating ATP in cells. It involves a series of protein complexes located in the mitochondrial inner membrane, which pump protons (H ions) across the membrane to create a proton gradient. This gradient is essential for ATP synthesis.
**Why the Correct Answer is Right**
The correct answer is related to the function of each complex in the mitochondrial ETC. The complexes that pump H ions are responsible for creating the proton gradient. Complex I (NADH dehydrogenase) and Complex III (cytochrome b-c1 complex) pump H ions into the intermembrane space. Complex II (succinate dehydrogenase) is part of both the ETC and the citric acid cycle and does not pump H ions. Complex IV (cytochrome oxidase) pumps H ions into the intermembrane space as well. Complex V (ATP synthase) uses the proton gradient to produce ATP.
**Why Each Wrong Option is Incorrect**
* **Option A:** Not applicable, as the question does not specify a particular complex.
* **Option B:** This is incorrect because Complex I (NADH dehydrogenase) and Complex III (cytochrome b-c1 complex) pump H ions into the intermembrane space.
* **Option C:** This is incorrect because Complex IV (cytochrome oxidase) also pumps H ions into the intermembrane space.
**Clinical Pearl / High-Yield Fact**
Inhibitors of Complex I, such as rotenone, can decrease ATP production and increase reactive oxygen species (ROS) production, leading to mitochondrial dysfunction.
**Correct Answer: C. Complex II (succinate dehydrogenase) does not pump H ions.**