Final answer:
The sequence of amino acids in a protein's polypeptide chain is known as the primary structure. This sequence is foundational for higher levels of protein structure, including the secondary, tertiary, and quaternary structures.
Step-by-step explanation:
The specific sequence of amino acids that makes up the polypeptide chain constitutes a protein's primary structure. In the context of protein structure, which is categorized into four levels, the primary structure refers precisely to this linear sequence of amino acids in the polypeptide. Once this sequence is established, the chain can fold into various shapes, forming the secondary structure. The secondary structure commonly includes patterns such as the alpha-helix and the beta-pleated sheet, vividly seen in the folding of proteins. These structures are generally stabilized by hydrogen bonds in the protein's backbone.
Further folding and bonding result in the tertiary structure, which gives the protein its three-dimensional shape and is crucial for its specific function. The quaternary structure is present in proteins that consist of more than one polypeptide chain or subunit, including well-known examples like hemoglobin that contains four polypeptide chains. Each level of protein structure plays a significant role in determining the protein's properties and functions, with the primary structure serving as the foundation for the higher levels of organization.