In the protein adenylate kinase, the C-terminal region has the sequence Val-Asp-Asp-Val-Phe-Ser-Gln-Val-Cys -Thr-His-Leu-Asp-Thr-Leu-Lys- The hydrophobic residues in this sequence are presented in boldface type. Suggest a possible reason for the periodicity in their spacing. a. Each residue that is hydrophobic lies on one side forming amphipathic α-helix. b. Hydrophobic residues give rise to a helical dipole moment and partial (-) charge of the C-terminus. c. Active site of the adenylate kinase is formed by packed together hydrophobic residues. d. Localization of hydrophobic residues on the one side of β-strand mediates the interactions with other one of the polypeptide chain.