Large Molecules Problem Set

Problem 12: Sequence of a longer polypeptide

Tutorial to help answer the question

A polypeptide 10 amino acids long is split into various smaller fragments, and the amino acid sequences of some of the fragments are determined. The identified fragments include: ala-gly-ser-gln, lys-trp-arg-pro, gln-his-lys, asp-ala-gly. What is the primary sequence of the polypeptide?

Tutorial

Amino acids of a polypeptide

As with the previous question, a key piece of information is that the length of the unknown polypeptide is 10 amino acids. What are the 10 amino acids that make up the unknown? This is determined by examining the sequences of the three fragments. Note that there are 10 different amino acids present in the three fragments. They are, in alphabetical order:

ala, arg, asp, gly, gln, his, lys, pro, ser, trp

Overlapping pieces

Since no amino acids are duplicated in this example, any amino acid found in two fragments identify an overlap. The four fragments overlapped as follows:

The original peptide must have the sequence of:

asp-ala-gly-ser-gln-his-lys-trp-arg-pro

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