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Calculate the isoelectric point (pI) of an amino acid

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Calculate the isoelectric point (pI) of each of the following amino acids
(a) glycine
(b) glutamic acid
(c) arginine

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Solution Summary

This type of question is common on introductory biochemistry exams and laboratory assignments, but students often find this calculation to be challenging. In this solution, a generalized "how to" step by step procedure is outlined so that students will be prepared to apply this method to future calculations. Then, the step by step solution (including structures) is shown for parts (a) and (b) of the problem. This step by step solution includes definitions of important concepts/terms. The step by step solution for part (c) is deliberately not shown, in order to encourage the student to work through the entire method on his/her own. Instead, the numerical answer is provided. After studying the solutions for parts (a) and (b), you will use the same approach for part (c) and be able to confirm your correct answer using the numerical answer.

Solution Preview

View the attachment below for the chemical structures.

The isoelectric point (or pI) of an amino acid is the pH at which the amino acid has a net charge of zero.

Step one: Consider the ionization of the amino acid. Draw the structures of the +1, 0, and -1 charged states of each amino acid.

Step ...

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