Chemistry 3.13- Amino Acids, Proteins and DNA

What are zwitterions?

• Since amino acids contain a basic amino group and an acidic carboxyl group, an intramolecular neutralisation reaction occurs

• This forms a zwitterion, which has both a positive (NH₃⁺) and negative (COO^-) charge

How do amino acids exist at different pHs?

• At a low pH, the presence of H⁺ ions will reprotonate the COO^- group in the zwitterion (reforming the COOH), so the amino acid will exist as a cation

• At a high pH, the presence of OH^- ions will deprotonate the NH₃⁺ group in the zwitterion (reforming the NH₂), so the amino acid will exist as an anion

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