Altius Covid Exam 1_Passage 7_Q39

Can someone explain why the correct answer choice is NOT 1) Dimer 2)unfolded?. My other question is how can we assume that ALL dimers are bigger when it clearly states in the passage in table 2, that an unfolded truncated monomer has larger predicted RS than folded dimer?

Thanks!

Hi,

This question is tough, recall that the MCAT wants you to pick the best answer.

It is true that stokes shifts are provided for NS-1-2 peptides, but note that the question is asking about a general dimer, folded monomer, and unfolded monomer. Therefore, it is not guaranteed that the specific data in Table 2 will apply to the question at hand.

What I would use to guide is that larger molecules migrate more quickly in size exclusion chromatography.

General size trends for proteins can be summarized as

Dimer ~ Unfolded monomer > Folded monomer

And Dimer > Monomer

From this we can eliminate A and C.

However, what this trend can't tell us is if the Dimer is always smaller than the unfolded monomer for all proteins. This could be true, but we don't

What this does however tell us with 100% certainty is that a dimer is larger than a folded monomer, making B a slightly better answer than D.

Again, D might be true, but as the MCAT asks for the best answer, B is slightly better as it is always true.

This type of question is among the most difficult on the MCAT.

Please let me know if this unclear.