What type of molecule is FAD?

FAD, or flavin adenine dinucleotide, is classified as a coenzyme. Coenzymes are non-protein molecules that play a critical role in the function of enzymes. They often act as electron carriers in metabolic reactions, facilitating the transfer of electrons during redox reactions.

FAD specifically participates in various biological oxidation-reduction reactions. It can be reduced to FADH2, which then carries electrons to the electron transport chain, contributing to cellular respiration and energy production. The role of FAD as a coenzyme is crucial in metabolic pathways, such as the Krebs cycle and fatty acid oxidation, where it assists in the enzymatic reactions by providing or accepting electrons.

The other categories—enzymes, hormones, and substrates—do not accurately define FAD. Enzymes are proteins that catalyze biochemical reactions, hormones are signaling molecules that regulate physiological processes, and substrates are the reactants that enzymes act upon in a biochemical reaction. Thus, recognizing FAD as a coenzyme reflects its essential function in supporting enzymatic activity and facilitating metabolic processes.