How many carbon and nitrogen atoms are there, respectively, in a single turn of an alpha-helix?
A)6 5
B)7 5
C)7 4
D)6 4
E)5 7

Question

Quizplus · Accepted Answer

In an alpha-helix, there are 3.6 amino acid residues per turn, and each amino acid contains a carbon atom and a nitrogen atom. Therefore, there are 3.6 carbon atoms and 3.6 nitrogen atoms in a single turn of an alpha-helix. However, the carbon atom of the carboxyl group at the end of the helix does not participate in the helical structure, so there are only 3.6-1=2.6 carbon atoms and 3.6-1=2.6 nitrogen atoms that are part of the helical structure. Rounding these values gives 3 carbon atoms and 4 nitrogen atoms, so the answer is C) 7 4.

How Many Carbon and Nitrogen Atoms Are There, Respectively, in a Single