How does ATP differ from ADP?

Hint: ATP is the energy currency of a cell and both ATP and ADP are important for all biochemical reactions that take place in living organisms. The main difference between ATP and ADP is the number of a phosphate group. Both also differ in structure, composition and functions.

Complete answer:
ATP stands for Adenosine triphosphate whereas ADP stands for Adenosine diphosphate, the basic difference between both ATP and ADP is the number of the phosphate group. The higher number of one phosphate in ATP makes a high chemical energy bond and due to this, the molecular mass of ATP is higher than ADP. High molecular mass makes ATP less dense therefore density of ATP is less than that of ADP. ATP generates through photophosphorylation, fermentation and respiration, whereas ADP generates through dephosphorylation of ATP by enzyme ATPase. In the biological system, ATP helps in cell metabolism, amino acid activation, macromolecules synthesis, transportation of molecules and the maintenance of cell structure whereas ADP in the biological system shows catabolic pathway during glycolysis, citric acid cycle, oxidative phosphorylation and blood platelet activation. In aerobic metabolism dephosphorylation of ATP builds ADP and AMP whereas the rephosphorylation of AMP and ADP produces ATP with the accumulation of energy in the cell.

Note:
Karl Lohmann first discovered and isolated ATP from muscle and liver extract but it was first synthesised chemically by Alexander Todd in the laboratory where its structure gets defined. Fritz Albert Lipmann proved that ATP is the energy currency of the cell because it synthesises and liberates energy during metabolic reactions.