In addition to DNA and RNA, a nucleotide is found in a molecule called adenosine triphosphate (ATP).
As you can see from the image below, adenine is part of ATP.
As the name ATP indicates, there are three phosphate molecules at the end of ATP. The two bonds shown in red are high energy bonds. (In many books, these bonds are illustrated with a squiggly line ~.
As you know, one of the reasons we eat food is in order to obtain energy from it. But cells aren’t able to utilize the energy directly. Rather, through a series of catabolic reactions, cells use the energy from breaking the bonds in food to make ATP.
ATP is used to perform cellular work, such as muscle contraction and a process called active transport.
Generally, cells tap into the energy of ATP by splitting off the last phosphate of ATP. When this happens, adenosine diphosphate results.
ATP is regenerating by using the energy of food molecules to combine ADP with a phosphate to make ATP. This process is called cellular respiration.
During intense exercise, when the ATP depleted and the regeneration of ATP through cellular respiration is fast enough to supply the amount of ATP needed for muscle contraction, cells use a chemical called creatine phosphate (CP) to replenish the ATP by splitting off the phosphate of creatine phosphate and attaching it to ADP to make ATP.