Adenosine triphosphate

Adenosine 5'-triphosphate (ATP) is an organic compound composed of adenine, the sugar ribose, and three phosphate groups. ATP serves as the major energy source within the cell to drive a number of biological processes such as photosynthesis, muscle contraction, and the synthesis of proteins. It is broken down by hydrolysis to yield adenosine diphosphate (ADP), inorganic phosphorus, and energy. ADP can be further broken down to yield adenosine monophosphate (AMP), additional phosphorus, and more energy. When the phosphorus and energy are immediately used to drive other reactions, such as the synthesis of uridine diphosphate (UDP), an RNA precursor, from uridine monophosphate (UMP), the pair of reactions are said to be coupled. New ATP is produced from AMP using the energy released from the breakdown of fuel molecules, such as fats and sugars.

Extracellularly, ATP has been found to act as a neurotransmitter. ATP receptors are widespread through the body. Often released in tandem with other neurotransmitters, by itself ATP is known to have effects in the arteries, intestines, lungs, and bladder.

Structure
The structure of ATP has an ordered carbon compound as a backbone, but the part that is really critical is the phosphorous part - the triphosphate. Three phosphorous groups are connected by oxygen atoms to each other, and there are also side oxygens connected to the phosphorous atoms. Under the normal conditions in the body, each of these oxygens has a negative charge, and the negative charges repel each other. These bunched up negative charges that are forced together in the molecule represent a great deal of potential energy waiting to be released.

Adenosine Monophosphate (AMP), which is ATP with two of the phosphate groups removed, is also known as the "A nucleotide" in DNA.