Final answer:
The alpha helix is an example of the secondary structure in proteins which is stabilized by hydrogen bonds within the polypeptide chain.
Step-by-step explanation:
The alpha helix is an example of the secondary structure of proteins. The secondary structure refers to the regular local patterns within a protein, and besides the alpha helix, another common form is the beta-pleated sheet.
Proteins have four levels of structure. The primary structure is determined by the sequence of amino acids in the polypeptide chain. The secondary structure, which includes the alpha helix, is maintained by hydrogen bonds between the backbone atoms in different turns of the helix.
The tertiary structure is the overall 3D shape of the protein that arises from interactions between the side chains of the amino acids. Lastly, the quaternary structure, present in some proteins, is the complex of multiple polypeptide chains, as seen in hemoglobin. The alpha helix is stabilized by hydrogen bonds forming between the carbonyl oxygen of one amino acid and the amide hydrogen of another, four residues earlier in the chain.