Which molecule functions as the cellular energy currency?

• A. NADH
• B. GTP
• C. FADH2
• D. ATP

Answer: (D)

Cells store and deliver energy in a form that can be spent quickly to do work. The molecule that serves as the cellular energy currency is ATP. It carries energy in the bonds between its phosphate groups, and when the terminal phosphate is removed in hydrolysis, energy is released to power processes like muscle contraction, active transport, and biosynthetic reactions. The resulting ADP and inorganic phosphate can be recombined to form ATP again, using energy from nutrients through cellular respiration or from light in plants.

NADH and FADH2 are electron carriers that shuttle high-energy electrons to the electron transport chain to help make ATP, but they’re not the immediate energy currency themselves. GTP is another high-energy molecule used in certain specific processes, such as some steps of protein synthesis and signaling, but ATP is the primary, universally used energy currency in most cellular activities.