ATP

Nucleotide molecule found in all cells. It can yield large amounts of energy, and is used to drive the thousands of biological processes needed to sustain life, growth, movement, and reproduction. Green plants use light energy to manufacture ATP as part of the process of photosynthesis. In animals, ATP is formed by the breakdown of glucose molecules, usually obtained from the carbohydrate component of a diet, in a series of reactions termed respiration. It is the driving force behind muscle contraction and the synthesis of complex molecules needed by individual cells.

In metabolism the food's energy is ‘captured’ in the form of ATP, to be used later when needed. Thus ATP is often called the ‘energy currency’ of the cell. When it is used, its chain of three phosphate groups is shortened to two, resulting in the compound ADP (adenosine diphosphate) and inorganic phosphate.

ATP is also required as a building block for the synthesis of RNA, along with the nucleotides CTP, GTP, and UTP.