Map Sapling Learning macmillan leaming α-Keratin is an intermediate filament with a basic structural unit of two α helices in a coiled coil. Each helix has a seven residue repeating unit (heptad repeat). A representation looking down the α helices of a coiled coil dimer is shown below. Each letter represents a different amino acid residue Identify the three true statements about the structure of keratin. Click here to view a table of the amino acids Leu-Lys-Asn-Val-Cys-Glu-Ser is a likely repeat in the α helix of keratin Keratin molecules are very strong due to hydrophilic interactions between charged amino acid side chains The α helix of the coiled coil is wound less tightly than predicted for an α helix Glu-Val-Ser-Cys-Ser-Lys-Thr is a likely repeat in the α helix of keratin α-Keratin is rich in Cys residues, enabling the formation of covalent cross-links between peptide chains and increasing the strength of the proteirn Each polypeptide in the dimer has 3.6 residues per turn, and a nonpolar group occurs every 3.5 residues, resulting in a slight winding, or twist, around the other polypeptide, forming a coiled coil The residues at positions b and c are less likely to be polar or charged because they are in contact with the solvent