Energy is defined as the capacity to do work. A living cell is never static. It is always performing some work like synthesis of enzymes, cell division etc. Therefore all biological process require energy to occur. This energy is provided to all living cells by ATP for performing their work. ATP is obreviated from Adenosine Tri Phosphate. It is an energy rich of energy.
A cell hydrolyses ATP to ADP and inorganic phosphate and almost 7.3 K cal of energynis released in the process. This energy is used by the living cell for its functions. ATP has three phosphates group. there are two types of phosphate bonds in ATP i.e the high energy phosphate bonds and low energy phosphate bonds. The high energy phophate bonds are represented by curved symbol (~) while the ordinary bonds are straight line in the formula. The high energy bonds yields more energy on hydrolysis while the low energy bonds yield less energy. When energy is required for any cellular activity, the high energy bonds are broken down, ATP is converted to ADP or AMP and energy is released.
Adenine is a nitrogenous base when covalently bonded to 5-C ribose sugar making a molecule called adenosine monophosphate (AMP). By the addition of another phosphate to AMP a molecule called adenosine diphosphate (ADP) is built. ATP is built when one more phosphate is added to ADP. The addition of phosphates uses energy which is obtained from the breakdown of glucose molecule in respiration.