Final answer:
The alpha helix is a type of secondary protein structure characterized by a right-handed spiral shape stabilized by hydrogen bonds every 3.6 amino acids. This structure is critical to protein function and is stabilized by interactions between the amino acids' side chains and the main chain.
Step-by-step explanation:
The alpha helix (a-helix) is a type of secondary structure found in proteins. Its distinctive spiral shape results from the polypeptide chain twisting into a helix. This configuration is stabilized by hydrogen bonds that form between the carbonyl oxygen atom of one amino acid and the amide hydrogen atom four amino acids up the chain, which is characteristic of a right-handed a-helix. X-ray crystallography has revealed that this helix makes one complete turn every 3.6 amino acids, with the R group or side chains of these amino acids projecting outward from the coiled backbone.
The a-helix is an integral part of a protein's three-dimensional structure, which plays a critical role in the protein's function. Certain amino acids have a propensity to form the a-helix, while others form structures such as the beta-pleated sheet (B-pleated). Whether a protein segment forms an alpha helix or another structure depends on the sequence of its amino acids and the interactions between their side chains and the main chain, particularly through hydrogen bonding.
Proteins like a-keratins, which compose hair and wool, primarily consist of the a-helical conformation. Meanwhile, other proteins may have different structures in various regions, such as hemoglobin and myoglobin, which are helical in certain sections. It is important to note that the alpha helix and beta-pleated sheet are not exclusive of each other; both can be present in the same protein molecule.