Final answer:
Trypsin is specific for basic amino acids and therefore cleaves next to lysine and arginine, while elastase has a smaller active site that favors small side chains like alanine, dictating its specificity.
Step-by-step explanation:
Trypsin and elastase are two enzymes with specific substrate preferences when it comes to cleaving peptide bonds in proteins. Trypsin is highly specific for basic amino acids, such as lysine and arginine, cleaving peptide bonds at the carboxyl side of these residues. In contrast, elastase has a different specificity and cuts next to small amino acids like alanine. The specificities of these enzymes are largely determined by the shape and characteristics of their active sites, which can accommodate only certain amino acid side chains.
In the case of trypsin, the enzyme's active site is structured in such a way that it can form strong interactions with the positively charged side chains of lysine and arginine, which are basic amino acids. This interaction is crucial for positioning the peptide bond for catalysis. Elastase, on the other hand, has a small pocket at its active site that favors smaller side chains like those of alanine, thus dictating its specificity as well. The precise fit between an enzyme's active site and the substrate's specific amino acid side chain is akin to a 'lock and key' model, ensuring that each enzyme only catalyzes specific reactions. Thus, the specific amino acid sequences adjacent to peptide bonds define the sites of action for these proteolytic enzymes.