NADH and FADH₂ are two very important molecules in metabolism — they act as energy carriers that help the cell produce ATP, the main source of energy.
Here’s a simple explanation of their role:
- Energy Carriers:
During the breakdown of nutrients like glucose and fatty acids (in glycolysis, the Krebs cycle, and beta-oxidation), electrons and hydrogen atoms are released.- NAD⁺ and FAD capture these high-energy electrons, becoming NADH and FADH₂.
- This means they store energy temporarily in the form of electrons.
- Transporting Electrons:
NADH and FADH₂ carry these electrons to the electron transport chain (ETC) in the inner membrane of the mitochondria. - ATP Production:
- In the ETC, NADH and FADH₂ release their electrons, which move through a series of proteins.
- As electrons pass along, energy is released and used to pump protons (H⁺) across the membrane.
- This proton flow drives ATP synthase to produce ATP from ADP and phosphate.
- Regeneration:
After donating their electrons, NADH and FADH₂ are converted back to NAD⁺ and FAD, ready to be used again in other metabolic reactions. - Energy Yield:
- Each NADH molecule can produce about 3 ATP molecules.
- Each FADH₂ molecule can produce about 2 ATP molecules.
In short:
NADH and FADH₂ act like rechargeable batteries in metabolism — they pick up high-energy electrons during food breakdown and deliver them to the electron transport chain, where their energy is used to make ATP for the cell’s activities.