Peptides are short snippets of protein amino acid sequences, typically between 5 and 25 amino acids in length. In so-called "bottom-up" proteomics mass spectrometry, peptides are explicitly created as part of the sample prepation process. Specifically, an enzyme, typically trypsin, is added to the samples to cleave the protein into multiple small parts (peptides) at specific cleavage points. For trypsin, those cleavage points are at the amino acids K or R, unless the following amino acid is P.