sapling earning a-Keratin is an intermediate filament with a basic structural un
ID: 34257 • Letter: S
Question
sapling earning a-Keratin is an intermediate filament with a basic structural unit of two a helices in a coiled coil. Each helix has a seven residue repeating unit (heptad repeat). A representation looking down the a 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 atable of the amino acids. Glu-Val-Glu-Ser-Glu-Lys-Lys is a likely repeat in the a helix of keratin. Keratin molecules are very strong due to hydrophilic interactions between charged amino acid side chains. 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. Leu-Lys-Asn-Val-Ser-Glu-Glu is a likely repeat in the a helix of keratin. o Keratin is rich in Cys residues, enabling the formation of covalent cross-links between peptide chains and increasing the strength of the protein. The a helix of the coiled coil is wound less tightly than predicted for an a helix.Explanation / Answer
The statements 3, 6 and 7 are true. In alpha helix, the coiled polypeptide contain 3.6 residues per turn and placing the nonpolar residues at every 3.5 in the turn to reduse the repulsion between the like charged amino acids and as well as to main rigid stability of the helix. The alpha keratin contains high amounts of cysteine residues forming disulfide bridges and covalent cross linkings to provide great strength to the the protein. The supercoiled or coiled coil structure of helix is less tightly packed than the alpha helix because the alpha helix is generally right handed and the coiled coil exist in left handed confirmation.
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