Explain how the formation of peptide bonds and subsequent folding of a polypeptide leads to a protein with a specific three-dimensional shape.

Peptide bonds are formed by a condensation reaction between the amino group of one amino acid and the carboxyl group of the next, releasing a molecule of water. The sequence of amino acids – the primary structure – is dictated by the gene and the codon sequence, and this sequence determines the pattern of side‑group interactions that drive folding. In the polypeptide backbone, hydrogen bonds between the N–H and C=O groups give rise to regular secondary structures such as α‑helices and β‑pleated sheets. Finally, the polypeptide folds into its specific tertiary (and, if applicable, quaternary) structure, a process stabilised by interactions between the R‑groups: hydrogen bonds, ionic bonds, disulfide bridges and hydrophobic packing.