What happens to NADH in Complex 1 of the electron transport chain?

In Complex I of the electron transport chain, NADH plays a crucial role in cellular respiration. When NADH enters Complex I, it donates electrons derived from the oxidation of NADH to the electron transport chain. This process involves the reduction of the flavin mononucleotide (FMN) within Complex I, which then facilitates the movement of electrons through a series of iron-sulfur clusters.

As NADH donates its electrons, it is oxidized back to NAD+. The key processes occur as electrons are transferred to ubiquinone (coenzyme Q), which becomes reduced to ubiquinol as it accepts electrons from Complex I. This electron transfer is coupled with the pumping of protons (H+) from the mitochondrial matrix into the intermembrane space, creating a proton gradient that is vital for ATP synthesis in subsequent steps of cellular respiration.

Thus, during this process, NADH does not simply drop protons; it is indeed oxidized to NAD+, and the electrons are used to reduce ubiquinone. Therefore, the correct understanding of what occurs in Complex I relates intricately to the oxidation of NADH and the translocation of protons rather than the indications given in the other options.