Consider whether the following statements are reasonable (R) or unreasonable (U)

Question

Consider whether the following statements are reasonable (R) or unreasonable (U) in terms of what you know of the stuctures and properties of proteins. Indicate either R or U for each statement and write a brief justification for your answer for those statements you judge as unreasonable.

(A) Only the hydrogen bonds that are surface-exposed are important in stabilizing the three dimensional structure of a globular protein.

(B) Polylysine (a polymer of lysine monomer units linked by alpha-peptide bonds) is likely to fold into an alpha helical structure at pH 7.0

(C) A coiled-coil protein possesses alpha helices that contain only hydrophobic amino acid residues.

(D). Interactions between hemoglobin subunits are stabilized in high salt concentrations.

(E) Alpha helices are commonly found in the interior of globular proteins

Explanation / Answer

(A) R-Unreasonable. Because the tertiary structure of protein is stabilized not only by hydrogen bonds, but also by hydrophobic interactions, Van Der Waals forces and electrostatic interactions.

(B)Unreasonable, because poly-lysine exists at random coil formation and it exists at alpha-helical structure at above10.3 pH only but not at pH 7.

(C) Reasonable, because the coiled-coil structures contain hydrophobic residues.

(D) Reasonable, because at high salt-concentrations keep the hemoglobin at more stabilized structure as the sub units of hemoglobin are stabilized in high salt concentrations.

(E) Reasonable, because in the interior of globular proteins more than 40% of alpha helices are there.

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