Where does the ADP comes from?
ADP or adenosine diphosphate is a molecule that is typically studied for its role in providing energy to the body. The main energy molecule in our body is adenosine triphosphate or ATP, which is generated during cellular respiration. One pathway for generation of ADP molecule is breakdown of ATP molecule. When the body requires energy, one of the phosphate groups is broken off from ATP, resulting in a net release of energy as new bonds are formed. Chemically, this reaction can be written as:
`ATP + H_2O -> ADP + Ph`
where, Ph represents a phosphate group. An estimated 30.5 KJ of energy is released for every mole of ATP molecule undergoing this reaction.
Another pathway for production of ADP molecule is from AMP (adenosine monophosphate).
AMP + ATP -> 2 ADP
ADP molecules can be converted back to ATP molecules by the addition of a phosphate group.
Hope this helps.