Amino acids are synthesized utilizing energy in the form of ATP. The cell regenerates ATP from ADP continuously, by catabolizing glucose as a primary energy source. It is estimated that the cell is only able to capture about 1/3 of the chemical energy stored in glucose and transfer it to ATP, to be utilized in the construction of amino acids and proteins. The remainder is lost as heat. Some amino acids are consumed as proteins in the diet, which are broken down into amino acids which can be utilized for protein synthesis, or catabolized and used as another source of energy.