Proteases are basically proteins that break down other proteins. They cleave the peptide bonds that link amino acids together. Proteases also have many functions. Proteases such as pepsin and trypsin break down proteins in food so that it can be absorbed into the blood for further metabolism. Certain proteases destroy harmful proteins. For example white cells use these proteases to break down bacteria and parasites. There are also many biological and regulatory functions of the proteases.