What characterizes the tertiary structure of a protein?

The tertiary structure of a protein is characterized by the overall three-dimensional shape that arises from the interactions between the various amino acids in the polypeptide chain. This structure is determined by the specific positioning of amino acid side chains, which can involve various types of interactions, such as hydrogen bonds, ionic bonds, hydrophobic interactions, and disulfide bridges. These interactions cause the polypeptide chain to fold and twist into a unique shape that is essential for the protein's function.

Option C highlights that further folding is dependent on amino acid positioning, which is crucial because the properties of the side chains dictate how the protein will fold. Different sequences of amino acids will yield different interactions, leading to diverse tertiary structures that allow proteins to perform their specific biological roles effectively. This understanding of protein structure is vital for comprehending how proteins function in biological systems.