Adenosine triphosphate (ATP) is a molecule composed of an adenine base, a ribose sugar structure, and a chain of three phosphate groups. The three phosphate groups are negatively charged and would like to get away from one another, but are unable to because they are covalently bonded. This results in large amount of potential energy in the bonds between the phosphate groups.
The energy in a bond between two phosphate groups can be liberated when an ATP molecule interacts with a water molecule. The liberation of a phosphate group from ATP by water is called the hydrolysis of ATP:
ATP + `~H_2O` -> ADP + `P_i`
In the reaction shown above, ADP stands for adenosine diphosphate. `~P_i` represents the liberated phosphate group.
The hydrolysis of ATP to ADP generates 30.6 kJ/mol of energy. This energy is used to power the cellular and physiological processes necessary for life.
Food energy is then used to convert ADP back to ATP. The ATP molecule stores the energy until it is needed.
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