ATP

ATP: (Adenosine Tri-phosphate):

The cell’s Energy Currency:      Major energy currency of all cells is nucleotide called Adenosine Tri-phosphate (ATP). As ATP plays central role as the energy currency in all organisms, it must have appeared early in the history of life.

The ability of ATP to store and release energy is because of the structure of ATP molecule. Each ATP molecule has three subunits.

(1) Adenine an organic molecule composed of two carbon nitrogen rings.

(2) Ribose, fine carbon sugar.

(3) Three phosphate groups in a linear chain.

The covalent bond connecting these phosphates is indicated by “tilde” symbol (–) and is high energy bond. The energy is not localized in the bond itself, it is property of entire molecule and is simply released as phosphate bond breaks. These bonds have low activation energy and breaks easily. The breaking of one bond releases about 7.3 K. Cal: (7300 calories) per mole of ATP.

The energy from ATP is sufficient to derive most of the cells endergonic reactions in a typical energy reaction only the outermost of the two high energy bonds, break. When this happens, ATP becomes ADP (Adenosine di-phosphate). In some cases ADP is further hydrolyzed to AMP (Adenosine mono-phosphate) as follows:

ATP ------------- > ADP + Pi + 7.7 K. Cal:

ADP ------------ > AMP + Pi + 7.3 K. Cal:

Cells contain reservoir of ADP and phosphate (Pi). As long as a cell is living, ATP is constantly being converted into ADP plus phosphate to drive the cells many energy requiring processes enabling the animal to perform biological work. ATP can not be stored for long, as ATP lasts only few seconds before it is used to perform biological work. Thus cells constantly recycle ADP, with the energy derived from food stuffs, stored fats and starches. ADP and phosphate recombine to form ATP, with 7.3 K. Cal: of energy per mole contributed to each newly formed high energy phosphate bond.