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    Net Electrical Charge

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    Calculate the net electrical charge for the below polypeptide sequence at pH 7.4


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    In order to solve this question, you need to know the pKa values for the amino acid ionizable R groups and the terminal NH2 and COOH groups.

    You'll need a table of pKa values. I'm using one from "Principles of Biochemistry" by Lehninger, Nelson, Cox (2 ed). You can use any similar table. It won't change your result much as the values should be very similar from table to table.

    What is a pKa? It is the pH at which the ionizable group exists in both the protonated and unprotonate forms to an equal extent, i.e. 50% of each.

    If we start with glycine at the N-terminus, we ask, "Are there any ionizable groups?" Yes, there is one, i.e. the N-terminal NH2 group of glycine. If you look it up in your table, you will see that its pKa is 9.6. So what? Now, you need to determine if ...

    Solution Summary

    565 words to calculate the net charge of a polypetide.