please help and explain as much as you can Question 5. Keratin is a \"coiled-coi
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please help and explain as much as you can Question 5. Keratin is a "coiled-coil" protein. Answer the following questions about keratin. (a) Keratin proteins have a "pseudorepeat" of how many residues? (b) At what positions are hydrophobic residues found in the pseudorepeat? (c) Why are there hydrophobic residues at those positions? (d) Polar residues are usually found at the remaining positions. Why? (e) Which of the following possible peptides is most likely to be a pseudorepeat? (pick only one) a. D-Q-I-E-V-E-R b. W-Q-E-Y-E-R-D c. I-Q-E-V-E-R-D (1) What is wrong, or less good, about the other two possibilities? Question 6. (a) Using the table of AA propensities from the book, rate each of the three peptides below for its likelihood to be found in either an 0-helix or a 0-sheet, by adding up the values for each amino acid in each conformation (b) Now, check each peptide for "sequence busters amino acids and groups of amino acids that are hardly ever found in helices or sheets (these are listed in the text). (c) Pick the one sequence most likely to be in a helix and the one most likely to be in a sheet and justify your choice based on your work above in (a) and (b). (a) CRAGNRKIVLETY (b) SEDNFGAPKSILW (c) QKASVEMAVRNSGExplanation / Answer
5. a. Keratin proteins have a pseudorepeat or imperfect repeat of 7 residues : hXXhXXX where h stands for small hydrophobic amino acid like alanine or valine and X stands for any type of amino acid.
b. The structure of keratin protein is a coiled coil dimer. If you make a cross section and observe from top on one phase of cross section there is the position for small hydrophobic amino acid: a position. XXh is on the same side of alpha helix: d position.
c. Hydrophobic amino acids are arranged such a way that one side of alpha helix is completely hydrophobic.When two alpha helix come closer, two hydrophobic chain of amino acid make a very stable alpha helical arrangement.
d. Polar residues are found in remaining position to provide an amphipathic character to the keratin.
e. Peptide b is most accepted pseudorepeat because tryptophan (W) and tyrosine (Y) are more hydrophobic than isoleucine (I) and valine (V).
f. Peptide a can't act as a pseudorepeat sequence as there is no hydrophobic amino acids at a and d positions.
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