Protein Structure Workshop F18(1)-Word MAILINGS REVIEW VIE AaBbCcl AaBbc AaB AaB

Question

Protein Structure Workshop F18(1)-Word MAILINGS REVIEW VIE AaBbCcl AaBbc AaB AaBbCeD AaBbcl 1 Normal Heading 1 Title Subtitle Subtle Em.. Emphasis Paragraph 1. Answer the following questions concerning the polypeptides whose amino acid Styles sequences are shown below. Explain your reasoning for all. (1) Gly-lle-Trp-Leu-lle-le-Phe-Gly-Val-Val-Ala-Gly-Val-lle-Gly-Trp-lle-Leu-Leu-Leu (2) Gly-Pro-Asp-Gly-Pro-Met-Gly-Pro-Ser-Gly-Pro-Arg-Gly-Pro-Glu-Gly-Pro-Asp-Gly (3) Gly-Met-Trp-Pro-Glu-Met-Cys-Gly-Glu-Pro-Ala-His-Val-Arg-Asp-Tyr-Pro-Leu-Leu (4) Gly-Met-Trp-Pro-Glu-Met-Cys-Gly-Glu-Pro-Ala-His-Val-Arg-Asp-Tyr-Cys-Leu-Leu a. Which would be most likely to form an -helical structure? b. Which could have at least one disulfide bond? c. Suppose that the first amino acid residue in peptide (1) were altered from G to Pro. Would you expect this change to have an effect on the secondary structure of this peptide? Why or why not? 2. The protein hormone insulin is synthesized as a prohormone and is processed by cleavage of two peptide bonds to yield the mature hormone, which consists of two separate polypeptide chains, A, and B, linked by disulfide bonds. A denaturation/ renaturation (similar to the one carried out by Anfinsen with ribonuclease) experiment was carried out using insulin. However, in contrast to Anfinsen's results, only less than 10% of the activity of insulin was recovered when urea and -mercaptoethanol were removed by dialysis. (This is the level of activity you would expect if the disulfide bridges paired randomly.) In contrast, if the experiment is repeated with proinsulin, full activity is restored upon renaturation. Explain these observations.

Explanation / Answer

1.a "MALEK" which stand for methionine, Alaine, leucine, glutamate , lysine are known as alpha helix forming amino acid. Hence, according to the sequence of amino acid,  

These amino acid are maximum present in third sequence, hence, option c is correct.

1.b Since disulphide bond is formed between two cystein amino acid. As, in the last amino acid sequence, two cysteine are present , fourth sequence has a high probability of forming at least one disulphude bond

1.c There will not be any affect while changing in secondary structure because both glycine and praline are Aplha helix breaker amino acid.

2. These observation was because insulin prohormone contain extra stretch of small peptide which is called as C peptide. Mature hormone of insulin does not contain C peptide.  

3. Parallel beta sheet is joined by alpha helices because it will help in the formation of hydrogen bond between two parallel sheet.

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