In species X a critical polypeptide has the following amino

In species X a critical polypeptide has the following amino acid sequence: met-ala-cys-cys-phe-try-phe-pro. The amino acid sequence of five other species is determined. Which of these species is probably LEAST related to Species X? [mark all correct answers] a. met-ala-cys-cys-phe-try-ile-pro b. met-ala-ser-cys-arg-try-phe-pro c. met-ala-ser-cys-phe-try-phe-pro d. met-ala-cys-cys-phe-arg-phe-pro e. met-ala-cys-cys-phe-try-phe-glu

Solution

The correct answer is:

b. met-ala-ser-cys-arg-try-phe-pro

The species X has the amino acid sequence met-ala-cys-cys-phe-try-phe-pro. The species B is LEAST related to Species X. Since the above sequence lack a cystiene amino acid which is important in making disulfide bridges (secondary structure of proteins), this species is probably LEAST related to Species X.