NADH and FADH2 are molecules that play a central role in how our bodies convert the food we eat into usable energy. These molecules are coenzymes, meaning they are small organic molecules that assist enzymes in carrying out biochemical reactions. They are derived from B vitamins, specifically niacin for NADH and riboflavin for FADH2, highlighting the importance of these nutrients in metabolic processes. Their primary function involves facilitating cellular respiration, which is the body’s method of extracting energy from glucose and other fuel sources.
NADH and FADH2 as Electron Carriers
NADH (nicotinamide adenine dinucleotide) and FADH2 (flavin adenine dinucleotide) are electron carriers that pick up and transport high-energy electrons. They collect electrons and associated protons released during food breakdown. For instance, during glycolysis and the Krebs cycle, NAD+ and FAD are converted into NADH and FADH2 as energy is released.
NADH and FADH2 primarily carry high-energy electrons to a specific cellular location for processing. Each NADH molecule carries two electrons and a proton, while each FADH2 molecule carries two electrons. This transport is important because the energy within these electrons must be delivered to the cell’s energy production system in a controlled manner. Without these specialized carriers, food energy could not be efficiently harnessed to power cellular functions.
The Electron Transport Chain
The high-energy electrons transported by NADH and FADH2 are delivered to the electron transport chain (ETC), the main energy production system within cells. This chain is a series of protein complexes located in the inner membrane of the mitochondria, the cell’s power plants. NADH donates its electrons to the first complex, and FADH2 delivers its electrons to a later complex.
As these electrons move sequentially through the protein complexes in the mitochondrial membrane, their energy is gradually released. This energy pumps protons (hydrogen ions) from the inner mitochondrion compartment into the intermembrane space. This pumping action creates a high concentration of protons, forming a proton gradient, similar to water held behind a dam.
The accumulated protons then flow back across the inner mitochondrial membrane, moving down their concentration gradient, through a specialized enzyme called ATP synthase. This proton flow powers ATP synthase, generating adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and inorganic phosphate. ATP is the cell’s primary energy currency, and its production is efficient. Oxygen is important for this process, acting as the final electron acceptor at the end of the chain, combining with protons to form water.
Why Cellular Energy Matters
The ATP molecules generated by NADH, FADH2, and the electron transport chain are important for nearly all cellular activities. This energy powers functions that keep an organism alive. For instance, ATP provides the energy for muscle contraction.
ATP is also important for nerve impulses, enabling communication throughout the nervous system. The synthesis of new proteins, the building blocks and functional molecules of cells, also relies on ATP. ATP fuels active transport processes, moving molecules across cell membranes against their concentration gradients, maintaining the cell’s internal environment. Without continuous and efficient ATP production, cells would lack the energy to perform these functions, impacting overall health and survival.