Two proteins (I and II), MWr 30,000, are isolated from homologous cells of close

Question

Two proteins (I and II), MWr 30,000, are isolated from
homologous cells of closely related organisms, and their primary
structure determined. The primary structure of protein I is
identical to that of protein II except for a short sequence
which in protein I reads:
-thr-phe-gly-lys-thr-val-tyr-glu-gly-leu-gly-asn-pro-
and which in protein II reads:
-ser-val-gly-glu-ser-phe-tyr-arg-leu-gly-asn-pro-.
Discuss briefly whether the structural or functional roles of
these proteins will be the same in their respective cells.
Include a discussion of
a) the probable 2° structure formed by each of the two
peptides and the reasons for your answer,
b) whether I and II could be the same protein, and
c) if the organisms from which I and II are extracted could
belong to the same species.

Explanation / Answer

The difference in the sequence of the segments from protein 1 and 2  can be shown as:   Phe-gly-Lys-Thr-Val-Tyr-Glu-Gly-Leu-Gly-asn-pro Ser-val-Gly-Glu-Ser-Phe-Tyr-Arg-Leu-Gly-asn-pro ------------------------------- The difference in sequence has been highlighted. ------------------------------ a) Hence the two proteins will have pleated sheet as its secondary structure as proline is present which blocks the formation of the -helix. ----------------------------  b) protein 1 and 2 may not be the same protein. ------------------------------ c) The two proteins might not belong to the same species but may belong to closely related species as they have a small segment of difference.  ---------------------------------------------   With this difference these two proteins may not have the same structural and functional roles in their cells. This can be confirmed by looking at the differences. An acidic amino acid is replaced by a aromatic amino acid. If an acidic amino acid is replaced by a similar amino acid then we can say that these 2 proteins may have the same role.   ----------------------------  b) protein 1 and 2 may not be the same protein. ------------------------------ c) The two proteins might not belong to the same species but may belong to closely related species as they have a small segment of difference.  ---------------------------------------------   With this difference these two proteins may not have the same structural and functional roles in their cells. This can be confirmed by looking at the differences. An acidic amino acid is replaced by a aromatic amino acid. If an acidic amino acid is replaced by a similar amino acid then we can say that these 2 proteins may have the same role. With this difference these two proteins may not have the same structural and functional roles in their cells. This can be confirmed by looking at the differences. An acidic amino acid is replaced by a aromatic amino acid. If an acidic amino acid is replaced by a similar amino acid then we can say that these 2 proteins may have the same role.    

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