Arrange the components of ETC used in sequence when ETC stas from FADH2: A. ATP synthase B. Cytochrome c Reductase C. Succinate dehydrogenase D. Cytochrome c oxidase
**Core Concept**
The electron transport chain (ETC) is a critical process in cellular respiration where electrons are passed through a series of protein complexes, resulting in the production of ATP. When the ETC starts from FADH2, it bypasses the first complex of the ETC, entering at the level of succinate dehydrogenase.
**Why the Correct Answer is Right**
When the ETC starts from FADH2, electrons are passed from FADH2 to succinate dehydrogenase (Complex II), resulting in the formation of FADH. These electrons then pass through the electron transport chain in the following sequence: succinate dehydrogenase (Complex II) → cytochrome b-c1 complex (Complex III) → cytochrome c oxidase (Complex IV). Finally, the energy generated from this electron transport is used by ATP synthase to produce ATP.
**Why Each Wrong Option is Incorrect**
**Option A:** ATP synthase is not part of the electron transport chain itself but rather the enzyme responsible for generating ATP from the energy produced in the ETC. It is located at the end of the ETC, not at the beginning.
**Option B:** Cytochrome c reductase (Complex III) is part of the electron transport chain but is not the correct starting point when the ETC begins with FADH2. It is located between succinate dehydrogenase and cytochrome c oxidase.
**Option C:** Succinate dehydrogenase is the correct starting point when the ETC begins with FADH2, but it is not the correct sequence of the components of the electron transport chain.
**Clinical Pearl / High-Yield Fact**
When the ETC starts from FADH2, it bypasses the first complex and results in a lower ATP yield compared to NADH, which enters the ETC at Complex I.
**Correct Answer:** C. Succinate dehydrogenase