ATP

Adenosine Triphosphate

Adenine base (Red), Ribose (Pink), Phosphate (Blue)

ATP (adenosine triphosphate) is a high energy molecule that is hydrolysed to provide energy for many reactions within the mammalian body. ATP is mainly synthesised in the mitochondria of a cell, in a process called oxidative phosphorylation, via electron transfer chain. A small amount of ATP is synthesised in the cytoplasm during glycolysis. ATP is a very important source of energy for many cellular functions, including in muscle contraction, active transport and condensation reactions. The molecular structure of ATP constists of three phosphate groups linked to an adenosine core. These phosphate groups are linked in series by two phosphoanhydride bonds .

ATP Hydrolysis

Hydrolysing ATP to ADP (adenosine diphosphate) or further to AMP (adenosine monophosphate) releases a large amount of free energy, because the phosphoanhydride bonds in the molecule are broken . ATP is, however, a very stable molecule and will only release its energy in the presence of ATPase.

What makes ATP an efficient energy source

ATP is the most common energy source in most cellular metabolism. However, some other cellular metabolism were not driven by ATP. Such an example of the other energy currency used in cellular metabolism is guanosine triphosphate(GTP), uridine triphosphate(UTP), and cytidine triphosphate(CTD). Nonetheless, ATP is the most efficient energy source used in cellular metabolism. The reasons that ATP is more reliable than the other nucleoside triphosphate in producing energy are:

• ATP have an unstable structure compared to ADP. Thus, ATP has a high phosphoryl-transfer potential (tendency to release phosphate to become ADP is high)
• At neutral, triphosphate of ATP have a great repulsion between each other. This is because, at pH 7, all the phosphate of ATP carries a negative charge. The electrostatic repulsion causes the phosphate group to be easily released.