Final answer:
Proline and glycine are amino acids that can break the regular α-helical pattern in proteins due to proline's rigid structure and glycine's flexibility.
Step-by-step explanation:
Some residues are helix-breaking, such as proline and glycine. Proline is known as a helix breaker because its rigid cyclic structure causes a kink in the α-helix and disrupts its hydrogen bonding pattern. Glycine, on the other hand, is so small that it provides too much flexibility to the backbone, which can also disrupt the helical structure. The α-helix is a common secondary structure in proteins, stabilized by hydrogen bonds between nearby amino acid residues in a polypeptide chain. Certain amino acids, like proline and glycine, have a lower propensity to be incorporated into an α-helix, therefore, when they are present, they can break the regular α-helical pattern.