Final answer:
The tertiary protein structure is the 3D shape of a protein that results from R-group interactions, including ionic bonds, hydrophobic interactions, and disulfide linkages.
Step-by-step explanation:
The protein structure that involves the formation of a 3D shape due to R-group interactions is known as the tertiary protein structure. This intricate structure is primarily due to the interactions among R groups within the polypeptide, which include ionic bonds, hydrophobic interactions, and the formation of disulfide linkages between cysteine side chains in the presence of oxygen. These interactions between the amino acids help give the protein its unique, complex three-dimensional tertiary structure, affecting its function and stability.