What is the role of NAD+ and FAD in cellular respiration?

NAD+ and FAD are crucial coenzymes that play a vital role in the process of cellular respiration, specifically in the transfer of electrons during metabolic reactions. Their primary function is to accept electrons during various stages of metabolism, such as glycolysis and the citric acid cycle (Krebs cycle). Once they accept electrons, NAD+ is reduced to NADH, and FAD is reduced to FADH2.

These reduced forms (NADH and FADH2) then transport the electrons to the electron transport chain embedded in the inner mitochondrial membrane. In the electron transport chain, the electrons are ultimately transferred through a series of protein complexes, which leads to the production of ATP through oxidative phosphorylation. This process is integral to generating energy for the cell.

Understanding the role of NAD+ and FAD as electron carriers highlights their importance in cellular respiration, contrasting with other options that suggest they directly provide energy, act as enzymes, or break down glucose, which are roles not attributed to these coenzymes.