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Beta Bends or Reverse Turns

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The amino acid sequence shown below represents a portion of a peptide bond obtained from a large protein:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
His - Ile -Thr - Arg - Phe - Phe - Pro - Cys - Met - Gly - Glu - Ala - Ile- Pro - His -

16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Thr - Glu - Asp - Cys - Gln - Met - Ile - His - Cys - Pro - Arg - Lys - Gln - Pro - Tyr

(a) Determine where the chain would be more likely to show beta bends or reverse turns.
(b) Discuss where one would fin cross-linked disulfide bonds in this sequence.
(c) Would you consider this molecule to be in alfa helix formation?

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Solution Preview

A "reverse turn" (also known as a "beta-bend") is where the polypeptide chain turns back upon itself. The amino acids with short polar side chains such as Ser, Asp, Asn, or no genuine side chain, like Gly and Pro, are usually found in reverse turns.

Therefore, if we take a look at the sequence, ...

Solution Summary

This solution deals with a "reverse turn" where the peptide turns against itself. This solution is 5 short paragraphs long.

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Amino Acids and Protein Structures

The amino acid sequence shown below represents a portion of a peptide obtained from a large protein.

Leu(1) His(2) Ile(3) Thr(4) Arg(5) Phe(6) Phe(7) Pro(8) Cys(9) Met(10) Gly(11) Glu(12) Ala(13) Ile(14) Pro(15) His(16) Thr(17) Glu(18) Asp(19) Cys(20) Gln(21) Met(22) Ile(23) His(24) Cys(25) Pro(26) Arg(27) Lys(28) Gln(29) Pro(30) Tyr(31) Leu(32)

Determine where the chain would be more likely to show β bends or reverse turns. Provide a clear explanation for your answer.

Discuss where one would find cross-linked disulfide bonds in this sequence.

Would you consider this molecule to be in an α-helix formation? Explain your answer.

Thank you!

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