Alpha helices and beta sheets have common structural motifs but can contain very

Question

Alpha helices and beta sheets have common structural motifs but can contain very different amino acid sequences. For each of the following, circle the correct structure that could form given that sequence.

A.        phe-leu-val-gly-ser-phe-leu-tyr-leu-gly-met-trp-leu-leu-phe-ile

amphipathic a helix                                   hydrophilic a helix            hydrophobic a helix

B.        Ile-ala-asn-thr-leu-gly-thr-ala-ile-gln-ser-ile-ala-cys-leu-leu

amphipathic a helix                                   hydrophilic a helix            hydrophobic a helix

C.        ser-ile-gln-leu-thr-phe-asn-met-glu-ile-glu-ala-thr-ile-arg-phe

amphipathic b sheet                                   hydrophilic b sheet             hydrophobic b sheet

D.        asn-thr-asp-ser-tyr-asp-met-thr-ser-his-thr-asn-leu-lys-thr-ser

amphipathic b sheet                                   hydrophilic b sheet             hydrophobic b sheet

Explanation / Answer

A. Answer is- Hydrophobic a helix, because there is long stretch of hydrophobic residues in amino acid sequence.

B. Answer is- amohipathic a helix, because polar and hydrophobic residues are disturbed 2-3 residues apart in the sequence, to produce an alpha helix with one hydrophilic face and one hydrophobic face; such a helix is known as amphipathic a helix.

C. Answer is- amphipathic b sheet , because a stretch of sequence with alternating hydrophobic and hydrophilic residues must have one hydrophobic and one hydrophilic face, forming an amphipathic beta strand.

D. Answer is hydrphilic b sheet, because there is alomost continuous hydrophilic residues chain, forming a hydrophilic b sheet.

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