4. A Ramachandran plot shows (A) the amino acid residues which have the greatest degree of rotational freedom, (B) the sterically allowed rotational angles between R groups and α-carbons in a peptide, (C) the sterically allowed rotational angles between Cα and the amide nitrogen (Cα-N) as well as between Cα and the amide carbonyl carbon (Cα-CO), (D) the sterically allowed rotational angles about the amide nitrogen (NH) and CO, (E) the amino acid residues that form α-helix, β-sheet, etc.