Question

A tetrapeptide is made of naturally occurring alanine, serine, glycine and valine. If the $C$-terminal amino acid is alanine and the $N$-terminal amino acid is chiral, the number of possible sequences of the tetrapeptide is

• A. 12
• B. 8
• C. 6
• D. 4

Answer 1

Answer: (D)

A tetra-peptide is made of naturally occuring alanine serine glycine and valine.
It is given that $C$-terminal amino acid is alanine and $N$-terminal amino acid as it is an achiral amino acid. Therefore possible sequence of tetra-peptide are as follows.
(i) Alanine, glycine, serine, valine
(ii) Alanine, glycine, valine, serine
(iii) Alanine, serine, glycine, valine
(iv) Alanine, valine, glycine, serine
Thus it can have $4$ possible sequences of the tetrapeptide.