Question

calculate the overall net charge of the following polypeptide at pH = 6.7

Met-Pro-His-Arg-Asp-Glu-Gln-Lys-Val-Phe

a. 0.39

b. -0.39

c. 0.61

d. -0.61

Answer 1

For calculation of net charge we have to know the pI [isoelectric point] of all amino acids of our protein .

For overall net charge we have sum up all the pI values and divide it by total number of amino acids [given].

In short we have to calculate the average of pI.

If the average of pI is lesser than the pH of protein the charge on protein is positive . If the average of pI is greater than the pH of protein the charge on protein is negative .

Let us calculate the average pI for our protein [see photo]

Our calculated pI is lesser than the pH of protein by 0.345 value so our correct answer is – option a [0.39]