Keratin is an intermediate filament with a basic structural unit of two helices
ID: 149613 • Letter: K
Question
Keratin is an intermediate filament with a basic structural unit of two helices in a coiled coil. Each helix has a seven residue repeating unit (heptad repeat). A representation looking down the helices of a coiled coil dimer is shown below. Each letter represents a different amino acid residue.
Keratin is an intermediate filament with a basic structural unit of two helices in a coiled coil. Each helix has a seven residue repeating unit (heptad repeat). A representation looking down the helices of a coiled coil dimer is shown below. Each letter represents a different amino acid residue. 9 9 Identify the true statements about the structure of keratin. Click here to view a table of the amino acids. Keratin molecules are very strong due to hydrophilic interactions between charged amino acid side chains. Val-Arg-His-Gly-Ser-Lys-Glu is a likely repeat in the a helix of keratin. The N-terminus of one helix is aligned with the C-terminus of the other helix in the dimer. Lys-Gly-Glu-Ser-Glu-Arg-Lys is a likely repeat in the a helix of keratin. The residues at positions b and c are less likely to be polar or charged because they are in contact with the solvent. The consequence of the coiled coil is that each alpha-helix in the dimer is wound tighter, has a smaller rise per turn, and twists around the other polypeptide.Explanation / Answer
Answer:
The first statement is correct.
The reason why these keratins are the strongest because of the ionic bond between the charged hydrophilic amino acids. More interestingly the amino acids are hydrophobic in nature where the alpha helix touches each other.
The second statement is wrong.
Keratin protein is rich in the amino acids like Cys, Met, Pro, Ala, Val, Leu, Ile, Met, and Phe.
The third statement is correct.
The C terminus of an alpha helix is aligned with the N terminus of the other alpha helix of the dimer
The fourth statement is correct.
The fifth statement is wrong.
The b and c residues in the structure are more likely to be polar or charged because they are in contact with the solvent. Hydrophobic amino acids at the surface will repel the polar solvent and the structure of the protein will be changed.
The sixth statement is correct.
Helices of keratin are arranged as a coiled coil. Two strands of keratin are wrapped about each other to form a supertwisted coiled coil. The supertwisting amplifies the strength of the overall structure. The twisting of the axis of an alpha helix to form coiled-coil results in the lesser distance that is 5.15 to 5.2 Å per turn instead of 5.4 Å per turn as predicted for an alpha helix by Pauling and Corey.
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