Amino acids, peptides and proteins

• A peptide is formed from two or more amino acid monomers, joined together by peptide bonds. These are formed during condensation reactions, releasing a molecule of water.
• Within a peptide, peptide bonds are formed between the COOH group of one amino acid, and the NH2 group of another amino acid. The OH from COOH combines with the H from NH2 to release H2O.
• Proteins can be hydrolysed through heating with concentrated hydrochloric acid. This breaks all peptide bonds, and all NH2 groups in the individual amino acids becomes NH3+ groups.
• Chromatography can be used to identify individual amino acids. Firstly, hydrolyse the peptide, then use a suitable solvent to observe the heights of each amino acid during chromatography. Calculate Rf values, and hence identify the amino acids.
• Since amino acids are colourless, a developing agent must be sprayed on an amino acid chromatogram in order to make their positions visible.
• The isoelectric point is the pH of an aqueous solution in which a certain amino acid is neutral.
• Zwitterions are molecules that contain positive and negative charges, but no overall charge.
• The mechanism of an amino acid acting as a base can be illustrated as follows: H2N-CHR-COOH + H2O ⇌ H3N+-CHR-COO- + OH-
• The mechanism of an amino acid acting as an acid can be illustrated as follows : H2N-CHR-COOH + H2O ⇌ H2N-CHR-COO- + H3O+