Trypsin is about 250 amino acids. Hit the Rotate buttons to get an idea of the shape of this enzyme. Hit the Distances button to get an idea of the size of this enzyme. Hit the button again to remove the distances.
All enzymes have chemical groups which perform the catalysis.
In the case of trypsin these are amino acid side chains. Note that some proteins utilize non-amino acid cofactors to help with the catalysis. Hit the Active Site Residues button to highlight the active site residues in Trypsin. Note that these same residues perform similar functions in other serine proteases. All enzymes have a site on their surface that binds substrate.