Sapting Learning -Keratin is an intermediate filament with a basic structural un

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Sapting Learning -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. Identify the three true statements about the structure of keratin. Click here to view a table of the amino acids. Val-Asp-Glu-Ala-Arg-His-Asn 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 helix of the coiled coil is wound less tightly than predicted for an helix The residues at positions b and c are less likely to be polar or charged because they are in contact with the solvent His-Ala-Asn-Arg-Asn-Asp-Gln is a likely repeat in the helix of keratin. -Keratin is rich in Cys residues, enabling the formation of covalent cross-links between peptide chains and increasing the strength of the protein. Previous Check Answer NextExit

Explanation / Answer

3 true statements about the structure of keratin are:

1. val-Asp-Glu-Ala-Arg-His-Asn is likely repeat in the alpha helix of keratin.

because karatin consist of heptad repeats basically inperfect repeats of 7 amino acids. The consensus amino acid sequence in heptamer of (-a-b-c-d-e-f-g-)n . residues a and d are non-polar. and valine and alanine are non polar amino acids.

2. each polypeptide in the dimer has 3.6 residues per turn, and a non polar group occurs every 3.5 residues , resulting in a slight winding or twist, around the other polypeptide, forming a coiled coil.

helix of the keratin has the similar structure as the traditional alpha helix. repeating heptamer of (-a-b-c-d-e-f-g-)n where residues a and d are non-polar made a point that  non polar group occurs every 3.5 residues.

3. alpha keratin is rich in cysteine residues, enabling the formation of covalent cross-links between peptide chains and increasing the strength of the protein.

alpha keratin have high cysteine content in their primary structure therehow also causes in increase of disulphide bond that are able to stabilize secondary structure and as we know that disulphide bonds are covalent bonds, provide strength to the protein

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