Final answer:
The folding of helix and beta-sheet regions in a polypeptide creates its tertiary structure, with secondary structures being alpha-helices and beta-pleated sheets.
Step-by-step explanation:
The folding of helical regions and beta-sheet regions relative to each other leads to the formation of a polypeptide's tertiary structure. The secondary structures, like the alpha-helix and beta-pleated sheet, are stabilized by hydrogen bonds. These hydrogen bonds form between the oxygen atom in the carbonyl group of one amino acid and an amino acid that is four residues down the chain. In the alpha-helix, these hydrogen bonds create a helical twist, and in the beta-pleated sheet, they result in a folded, pleated appearance. The tertiary structure arises when these secondary structures are further folded and arranged into a three-dimensional shape.