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:
A: 89.09
B: 132.65
C: 121.15
D: 133.1
E: 147.13
F: 165.19
G: 75.07
H: 155.16
I: 131.17
J: 131.2
K: 146.19
L: 131.17
M: 149.21
N: 132.12
O: 255.31
P: 115.13
Q: 146.15
R: 174.2
S: 105.09
T: 119.12
U: 168.06
V: 117.15
W: 204.23
X: 143.7
Y: 181.19
Z: 146.75
Notes
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
http://web.expasy.org/protparam/.
Molecular weights for J and X were taken from Geneious.