The molecular weight of a protein is calculated by adding up the molecular weights of the amino acids, per standard calculations.
In Benchling, the following molecular weights are assigned to amino acids:
We have lightly modified constants from biopython, to match results from expasy. These are the average isotopic masses, as opposed to the monoisotopic mass. See http://www.ionsource.com/tutorial/isotopes/slide8.htm.
Molecular weights for B and Z are non-standard and were reverse engineered from
Molecular weights for J and X were taken from Geneious.