Final answer:
Each NADH is capable of transporting three hydrogen ions into the intermembrane space through Complex I, III, and IV of the electron transport chain in cellular respiration. This process establishes the proton gradient necessary for ATP synthesis, with the energy efficiency of ATP production from NADH being around 42%.
Step-by-step explanation:
In the context of cellular respiration, NADH plays a critical role in the electron transport chain (ETC), which is part of the process that generates ATP, the energy currency of the cell. Electrons from NADH enter the ETC at Complex I, also known as NADH:quinone oxidoreductase, and release part of their energy. This energy is utilized to pump hydrogen ions (protons) across the mitochondrial membrane, from the matrix to the intermembrane space, creating a proton gradient.
Specifically, each molecule of NADH has sufficient energy to transport three hydrogen ions into the intermembrane space through Complex I, III, and IV. This gradient is essential for the production of ATP by the enzyme ATP synthase. In contrast, FADH2, which enters the ETC at Complex II, can only transport two hydrogen ions into the intermembrane space because it bypasses Complex I.
It is also important to note that the efficiency of ATP production from NADH is approximately 42%, with the remaining energy being dissipated as heat, which helps maintain body temperature. While the pumping of protons by NADH contributes to heat generation, the primary purpose is to facilitate the production of ATP.