Final answer:
Rotation around C-Cα and N-Cα determines the secondary structures of proteins, such as α-helices and β-pleated sheets, which rely on the orientation of the peptide backbone and hydrogen bonding. A protein's tertiary structure is formed by further folding and interaction among side chains. These structures are vital for the protein's function.
Step-by-step explanation:
Rotation around C-Cα and N-Cα determines the secondary structures of proteins. The rigidity of the peptide bond limits the peptide backbone's orientations, which are crucial for forming structures such as α-helices and β-pleated sheets. These structures are stabilized by hydrogen bonds between the carbonyl oxygen atom of one amino acid and the amide hydrogen atom four amino acids up the chain within the same or neighboring polypeptide chains.
The α-helix is a right-handed helix, making one turn for every 3.6 amino acids, with side chains projecting outward. Not all proteins are fully helical; for instance, α-keratins are exclusively α-helical, while others like hemoglobin contain helical parts. The β-turn, another secondary structure, allows for the reversal of the peptide backbone direction and is categorized into several types such as I, II, and VIII, among others.
Beyond secondary structure, protein folding also leads to a complex tertiary structure, influenced by interactions between side chains, including hydrophobic interactions and sometimes ionic bonds and disulfide linkages. Overall, the secondary structures and their specific arrangements contribute to the protein's final three-dimensional shape, essential for its function.