ATP is an abbreviation for adenosine triphosphate, a molecule present in the cytoplasm and nucleus of cells that stores energy from food and releases this energy to drive all physiological processes in the body. The components and bonding structure of ATP give it this crucial energy-storing capacity.
At the center of an ATP molecule is ribose -- a simple sugar containing a ring of five carbon atoms. Ribose is the same sugar present in ribonucleic acid (RNA), a strand of molecules crucial for protein synthesis and gene expression. This ribose molecule is not modified during the energy-releasing process that powers activity in the cell.
Connected to the side of the ribose molecule is adenine, a base which consists of nitrogen and carbon atoms in a double-ring structure. Adenine is also an important component of DNA. Its ability to bond with thymine in a strand of DNA accounts for the structure of human genetic material.
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The other side of the ribose molecule in ATP connects to a string of three phosphate groups. A phosphate group consists of a phosphorus atom joined to four oxygen atoms by covalent bonds. In the string of three phosphates, two of the oxygen atoms are shared between phosphorus atoms. This structure is what makes ATP an effective energy storage molecule.
Storing and Releasing Energy
When a water molecule is added to an ATP molecule, a chemical reaction takes place. ATP gives up one of its phosphates to the water molecule or to another molecule in a process known as phosphorylization. This chemical change is an exothermic reaction, meaning the process releases stored energy. The result of the reaction is adenosine triphosphate (ADP), which can store more energy obtained from sunlight or food by the addition of another phosphate group to the chain.