Which molecule is called the 'energy currency' of the cell?

ATP is a molecule found in all living cells. It stores and supplies the energy needed for almost all cell activities. It is called the "energy currency" of the cell because, just as money is earned in one place and spent in another, energy released from food is "stored" in ATP and then "spent" wherever the cell needs it.

ATP is made of three parts: adenine (a nitrogen base), ribose (a five-carbon sugar) and three phosphate groups. The bonds linking the last two phosphate groups are high-energy bonds. When the last phosphate group is removed by hydrolysis, ATP becomes ADP (adenosine diphosphate), and about 7.3 kilocalories (30.5 kJ) of energy per mole is released. The cell then uses energy from respiration to add the phosphate back, turning ADP into ATP again.

ATP is produced mainly in the mitochondria during aerobic respiration. One molecule of glucose can produce about 36-38 ATP molecules in aerobic respiration (modern estimates give about 30-32), but only 2 ATP in anaerobic respiration. Plants also make ATP in their chloroplasts during the light reaction of photosynthesis.

The energy from ATP is used for muscle contraction, the transmission of nerve impulses, the active transport of substances across membranes, the making of proteins and other molecules, cell division and the production of light in fireflies. ATP was discovered in 1929 by Karl Lohmann, and its role in energy transfer was later explained by Fritz Lipmann.

Why not the other options?

• ✗NADH carries electrons and hydrogen to the electron transport chain, where ATP is made.
• ✗Glucose is the main fuel from which energy is obtained, but the cell uses that energy through ATP.
• ✗Good to know
• ✗DNA carries genetic information, not energy.