Why are NADH and FADH2 considered high energy molecules?

NADH and FADH2 are considered high-energy molecules because they carry high-energy electrons that are generated during metabolic processes, such as glycolysis and the Krebs cycle. These electrons are transferred to the electron transport chain, where their energy is used to pump protons across the mitochondrial membrane, creating a proton gradient. This gradient drives ATP synthesis through oxidative phosphorylation, making NADH and FADH2 crucial for energy production in cells. Their ability to release energy upon oxidation defines their high-energy status.