BIOLOGY Volume 1 - A Guide to General Biology - 2004

3. CHEMICAL COMPONENTS OF LIVING MATTER

3.4. Amino Acids

3.4.2. Amphoteric Properties of Amino Acids

Compounds that, like Amino Acids, contain both a basic and an acidic group within their molecules are called amphoteric. They exist primarily as ions in which the basic moiety carries a positive charge and the acidic moiety carries a negative charge. These are known as dipolar ions, or zwitterions (Fig. 3.21). Amphoterism explains the ability of Amino Acids and Proteins to migrate in an electric field, a property utilized, for example, in their Separation by Electrophoresis Methods (Appendix 1, Vol. 3). The net charge of an amino acid can change depending on the environment. Thus, upon acidification of the solution, as the concentration of hydrogen ions increases, the positive charge of The amino acid also increases, while the negative charge is correspondingly neutralized.

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Fig. 3.21. Neutral zwitterionic form of an amino acid.