FL2 C/P Q13

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FL2 C/P Q13

Post by Amber9 » Thu Sep 05, 2019 2:07 pm

Q13 Can you clarify the explanation for the answer? Is it the near UV region because in the passage it mentions peptides NOT peptide bonds and peptides are part of a fully folded protein.

Thank you!
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Re: FL2 C/P Q13

Post by NS_Tutor_Mathias » Mon Sep 09, 2019 2:53 am

Hi there, glad to see you're working through your FLs!

So the passage tells us that asymmetry resulting from tertiary structural features causes a large increase in signal intensity in the near UV region and that the side chains of aromatic residues absorb in this region. So aromatic residues by themselves might show up as an increase in near UV signal, and asymmetry resulting from tertiary structural features might do so too, but both together would definitely produce the largest near-UV CD signal.

Answer a) talks about W as an isolated AA.

Answers b&c want you to realize that both alpha-helices and beta-sheets are secondary structures, and that the passage is only talking about tertiary structures giving rise to CD signal in the near UV region.

Of the options presented, only fully folded proteins can have a tertiary structure and therefore an asymmetric tertiary structure (the bulkiness of tryptophan would definitely contribute to this). This is the only option that can bring both factors together and create the largest possible increase in CD signal in the near UV region.
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