Identify the Pair of Peptides Below That CANNOT Be Distinguished

Question

Identify the pair of peptides below that CANNOT be distinguished by tandem mass spectrometry.
A) VTSPLYANEGK and VTCPLYANEGK
B) VTSPLYANEGK and VTSPLYADEGK
C) VTSPLYANEGK and VTSPIYANEGK
D) VTSPLYANEGK and VSTPLYANEGK
E) All of the answer choices are correct.

Accepted Answer

The difference between the two peptides in option C is the second amino acid, which is isoleucine and serine, respectively. However, these amino acids have the same mass, and therefore cannot be distinguished by tandem mass spectrometry. The other answer choices can be distinguished based on differences in amino acid sequence.