Question

A tetradecapeptide (14 amino acid residues) gives the following peptide fragments on partial hydrolysis. From this information, deduce the primary structure of this polypeptide. Fragments are grouped according to size. $$ \begin{array}{|l|l|} \hline \text { Pentapeptide Fragments } & \text { Tetrapeptide Fragments } \\ \hline \text { Phe-Val-Asn-Gln-His } & \text { Gln-His-Leu-Cys } \\ \hline \text { His-Leu-Cys-Gly-Ser } & \text { His-Leu-Val-Glu } \\ \hline \text { Gly-Ser-His-Leu-Val } & \text { Leu-Val-Glu-Ala } \\ \hline \end{array} $$

Short answer

Answer: The primary structure of the given tetradecapeptide is Phe-Val-Asn-Gln-His-Leu-Cys-Gly-Ser-His-Leu-Val-Glu-Ala.

Step-by-step solution

Analyze the overlaps between peptide fragments

First, let's look for overlaps between the pentapeptide and tetrapeptide lists to understand the connections between them. 1. Phe-Val-Asn-Gln-His has no overlap with any of the tetrapeptides. 2. His-Leu-Cys-Gly-Ser overlaps with Gln-His-Leu-Cys. Therefore, we know that the sequence is Gln-His-Leu-Cys-Gly-Ser. 3. Gly-Ser-His-Leu-Val overlaps with His-Leu-Val-Glu. Therefore, we know that the sequence is Gly-Ser-His-Leu-Val-Glu. Now, let's combine the two overlapping sequences we found in step 1 and the remaining pentapeptide fragment.

Combine overlapping sequences

We can now piece together the sequence by connecting the overlapping fragments: 1. Gln-His-Leu-Cys-Gly-Ser overlaps with Gly-Ser-His-Leu-Val-Glu. Therefore, the sequence is Gln-His-Leu-Cys-Gly-Ser-His-Leu-Val-Glu. 2. We still need to incorporate the remaining pentapeptide fragment, Phe-Val-Asn-Gln-His, which overlaps with the beginning of our current sequence at Gln-His. This gives us the complete tetradecapeptide sequence.

Write the complete primary structure

By connecting all the overlapping fragments, we find the primary structure of the tetradecapeptide to be: Phe-Val-Asn-Gln-His-Leu-Cys-Gly-Ser-His-Leu-Val-Glu-Ala This sequence contains 14 amino acid residues, as expected for a tetradecapeptide.