Final answer:
The primary structure is the level of protein structure that defines the number, kind, and sequence of amino acids in a protein's polypeptide chain, crucial for determining its function.
Step-by-step explanation:
The level of protein structure that refers to the number, kind, and sequence of amino acids is the primary structure. This organization level includes the linear sequence of amino acids in a polypeptide chain, which is held together by peptide bonds. Each protein's primary structure is unique and dictates the complex folding that leads to the higher levels of structure and ultimately, the function of the protein. For instance, the primary structure of insulin, which consists of 51 amino acids, determines how the hormone folds and interacts with cellular receptors.
Amino acids themselves are composed of a central carbon atom bonded to an amino group, carboxyl group, a hydrogen atom, and a distinctive side chain known as the 'R' group. The sequences in which these amino acids appear in the polypeptide dictate the protein's properties and role within an organism. The primary structure is critical because even a single change in this sequence could result in a malfunctioning protein, potentially leading to diseases.