Question 4. Calculate the length of a peptide that is comprised of 14 amino acid

Question

Question 4. Calculate the length of a peptide that is comprised of 14 amino acid residues in nanometers assuming: a) All residues in that peptide were adopting an alpha-helical conformation b) All residues in that peptide were adopting a beta-strand conformation 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-ID c. I-Q-E-V-E-R-D (f) What is wrong, or less good, about the other two possibilities?

Explanation / Answer

4. Distance between adjacent amino acids of 1.5 Å along an helix.
For 14 aminoacids 13 X 1.5 Å = 19.5Å or 1.95nm

Distance between adjacent amino acids along a strand is approximately 3.5 Å
For 14 aminoacids 13 X 3.5 Å = 45.5Å or 4.55nm

5. a. 7 residue pseudorepeat a-b-c-d-e-f-g

b. Residues at position a and d are hydrophobic.

c. They are responsible for the association of the two subunits through hydrophobic interaction.

d. Making alpha helix

e. C. I-Q-E-V-E-R-D

f. The other 2 peptide have polar aminoacids residues in 1st and 4 the position.

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