Final answer:
The alpha-helix structure and beta-pleated sheet are secondary structures of proteins, stabilized by hydrogen bonds that provide strength and stability, following the unique amino acid sequence known as the primary structure.
Step-by-step explanation:
The alpha-helix structure (a-helix) is a type of secondary structure in proteins, characterized by the polypeptide chain twisting into a spiral shape. It is stabilized by hydrogen bonds between the amino acid residues. These bonds occur between the carbonyl oxygen of one amino acid and the amide hydrogen of another. This repeated bonding makes the helix a strong and stable structure. The beta-pleated sheet (B-pleated), another form of secondary structure, consists of alternating rows of amino acids lying side-by-side, also stabilized by hydrogen bonding.
The secondary structure, be it alpha-helix or beta-pleated sheet, directly follows the primary structure, which is the unique amino acid sequence of the protein. The particular sequence determines the specific hydrogen bonds that form, influencing the protein's final shape, and thereby its function. Therefore, the secondary structure is critical for the protein's ability to perform its biological role.