Notes on Amino Acids and Peptides

Introduction to Amino Acids

• Basic units of proteins, 20 common, hundreds of derivatives.
• Weak polyprotic acids with multiple ionizable functional groups.
• All (except Proline) have at least an $\alpha$-amino group ($pKa \approx 9$) and an $\alpha$-carboxylic acid group ($pKa \approx 2$).
• Some have a third ionizable group in the R-group with its own $\text{pKa}$ value.
• Exist as dipolar ions at physiological $\text{pH}$.