Final answer:
The side chains of amino acids in an α-helix project outward from the helix's axis, facilitating hydrogen bonding every 3.6 residues and contributing to the protein's structural integrity.
Step-by-step explanation:
In the α-helix structure of a protein, the side chains of the amino acids project outward from the axis of the helix. This structural arrangement allows every helical turn in an alpha helix to consist of approximately 3.6 amino acid residues with the R groups, also known as the variant groups, extending outward.
The α-helix is stabilized by hydrogen bonds that occur between the carbonyl oxygen of one amino acid and the amide hydrogen of another that is four residues earlier in the sequence, creating a characteristic spiral shape.
In contrast, the β-pleated sheet's hydrogen bonding involves the backbone of aligned polypeptide chains, with the R groups extending above and below the folds of the sheet.
The α-helix is a common motif in globular and fibrous proteins and is crucial for the structural integrity of proteins, accommodating various types and sizes of side chains (side chains), without causing steric strain.
Figure 16.5.2 provides a model illustrating these features, with the green spheres representing the side chains.