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Chapter 28: Problem 36

Draw condensed structural formulas for the following amino acids buffered at \(\mathrm{pH}\) 6.0: (a) aspartic acid; (b) lysine; and (c) alanine.

Short Answer

Expert verified
The condensed structures of the three amino acids at pH 6.0 will be: aspartic acid in its deprotonated form (-COO-), lysine in its protonated form (-NH3+), and alanine in its neutral form.

Step by step solution

01

Identify the Isoelectric Point

First, determine the isoelectric points of each of the given amino acids. Aspartic acid has a pI of about 2.8, lysine has a pI of about 9.7, and alanine has a pI of about 6.0.
02

Compare the pH to the pI

Compare the given pH to the pI of each amino acid. At pH 6.0, the net charge on aspartic acid (pI 2.8) will be negative as pH > pI. For lysine (pI 9.7), it will be positive as pH < pI. For alanine (pI 6), the net charge will be zero as pH = pI. Determine the correct ionization state based on this.
03

Draw the Condensed Structural Formulas

Draw the condensed structural formulas for the amino acids in the identified ionization states. Since aspartic acid has a negative net charge, its carboxyl group (\(-COOH\)) is deprotonated to (\(-COO^-\)). For lysine, with a positive net charge, its amino group (\(-NH2\)) is protonated to (\(-NH3^+\)). Alanine will have a zero net charge, so it will not be ionized.

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