Which molecule is the main energy currency used by cells for most work?

• A. AMP
• B. ADP
• C. ATP
• D. NADH

Answer: (C)

Energy for most cellular work comes from ATP. The energy is stored in the bonds of the three phosphate groups, and when the cell needs energy, the terminal phosphate is removed, producing ADP and inorganic phosphate and releasing usable energy to power processes like muscle movement, transport across membranes, and making new biomolecules. ATP can be quickly regenerated from ADP using energy from nutrient molecules (or light in plants), so it’s always ready to supply energy where it’s needed. Other molecules aren’t used as the primary energy currency: AMP and ADP have less energy stored in their phosphate bonds, and while NADH carries high-energy electrons to drive ATP production, it isn’t directly used to perform work in the cell. ATP is the main energy currency because it is readily hydrolyzed to power diverse cellular activities and efficiently replenished.