Which molecule acts as the energy currency to power cellular reactions?

• A. NADH
• B. ATP
• C. Glucose
• D. ADP

Answer: (B)

Energy currency in cells is ATP. It stores energy in its three phosphate bonds, and when the terminal phosphate is cleaved to form ADP and Pi, a burst of energy becomes available to drive endergonic reactions and cellular work like muscle movement, transport, and biosynthesis. Because ATP can be continuously regenerated from ADP using energy from nutrients or light, it serves as a ready-to-use energy shuttle for countless processes. NADH is an electron carrier that donates high-energy electrons to the respiratory chain to help power ATP production, not the direct energy source for every reaction. Glucose is a fuel that provides energy by being oxidized to generate ATP, but it is not the immediate energy currency itself. ADP is the lower-energy form that ATP is made from and cannot power reactions on its own.