Final answer:
The chain of amino acids that folds upon itself forms the protein's secondary structure, comprising mainly of alpha-helix and beta-pleated sheet formations, which are stabilized by hydrogen bonds.
Step-by-step explanation:
The chain of amino acids that forms and folds upon itself is known as the protein's secondary structure. This structure includes common patterns such as the alpha-helix and the beta-pleated sheet. In the alpha-helix structure, hydrogen bonds form between the oxygen atom in a carbonyl group of one amino acid and the hydrogen atom of the amino group that is just four amino acid units farther along the chain. This creates a spiral shape, which is stabilized by these hydrogen bonds. In the beta-pleated sheet, the polypeptide chain folds back upon itself or between adjacent polypeptide chains, and hydrogen bonds form between carbonyl and amino groups, resulting in pleated sheet structures. Both of these structures are critical for the protein's ultimate function and stability.