Amino acids, proteins and DNA

Amino acids, peptides and DNA

α-Amino acids have NH₂ and COOH on the same carbon. In solids and at their isoelectric point they exist as zwitterions $\mathrm{H_3N^+CHRCOO^-}$ (high melting points, soluble in water). In acid they become cations; in alkali, anions. Two amino acids join by condensation, forming a peptide (amide) link –CONH– and water. Proteins are hydrolysed by hot 6 mol dm⁻³ HCl. Amino acids separate by electrophoresis (move by charge at a given pH) or chromatography. DNA: two sugar-phosphate strands held by hydrogen bonds between bases: A–T (2 H-bonds) and C–G (3). Cisplatin binds to guanine N atoms, stopping DNA replication in cancer cells.