The degradation of proteins occurs within the cells, as the amino acids have to pass through certain membranes before being able to be used for different processes. This first step to protein catabolism is breaking the protein down into amino acids by cleaving their peptide bonds, also known as proteolysis. The peptide bonds are broken up by the proteasome, which is able to hydrolyze the peptide bonds by using ATP energy. This process is further helped by the use of enzymes called proteases. The proteases help cleave off the remaining peptide residues to produce individual amino acids, ready to be converted into usable molecules for either glycolysis or the TCA cycle, to produce energy for the organisms, or to be used to create new proteins.