Question

How would you calculate the molecular weight of a protein?

Answer 1

Hint: Once a protein is isolated in a laboratory, the common method to estimate its molecular weight is by running the protein on SDS-PAGE. A marker dye is run along with it to know the molecular weight of the protein. The molecular weight of a protein can also be determined by knowing its chemical formula.

Complete answer:
It is important to determine the molecular weight of a protein. For many experiments or techniques molecular weight of the protein plays a crucial factor. If the sequence of amino acids is known for any given protein, we can roughly estimate the molecular weight of the protein by multiplying the average molecular weight of amino acids with the total number of amino acids present in the protein.
The average molecular weight of an amino acid is known to be 110 Daltons(Da).
Thus, for example, if we need to calculate the molecular weight of the nonapeptide hormone, oxytocin, all we need to do is multiply 110 with 9 to get the approximate molecular weight of the hormone.
If proteins are modified either by glycosylation or ubiquitination, the average molecular mass of the protein increases. For example, ubiquitin has a molecular mass of 8.5kDa.

Note: As mentioned earlier if the chemical formula of the protein is known the mass could be calculated by multiplying the subscript of each element by its atomic weight on the periodic table. Molecular weights are relative values and have no unit. However, scientists often use the unit ‘Da’ for Daltons, or ‘u’ for atomic mass units when writing atomic weight and molecular weight.