Question 6 (1 point) Answer the following questions based on these four protein

Question

Question 6 (1 point) Answer the following questions based on these four protein sequences. Use each sequence description ( turn, strand, -helix) only once. 1. Which sequence looks as if it could include a turn (reverse turn)? y lle-Gln-Ser-Ala-Leu-Asn- Glu-lle-Glu-Asn-Phe-Met- Ser-Cys-Val 2. Which sequence looks as if it could form a strand, with one surface facing the interior of the protein, and the other surface exposed to y lle-Asn-Leu-Glu-Met-Asp- Leu-Arg-Val-Gln-Leu-Glu- Phe-Lys-Val water? Val-Asn-Tyr-Gly-Pro-Gln- Which sequence looks as if it could form an amphipathic -helix? (Use a helical wheel to help) 3. GIn-Cys-Val

Explanation / Answer

Ans:-

(1) The Sequence 3 which is Val-Asn-Tyr-Gly-Pro-Gln-Leu-Phe-Ala-Leu-Val-Arg-Gln-Cys-Val looks as if it could include a Beta Turn (Reverse turn).

Reason is that, Reverse turns include both polar as well as nonpolar amino acid residues in it and Proline residue is commonly found in Beta turns which can adopt both PHI and PSI angles. The Pro residues provide rigidity to the structure of Beta Turns. Glycine (Gly) residues are also frequently found in beta turns.

(2) The Sequence 2 (Ile-Asn-Leu-Glu-Met-Asp-Leu-Arg-Val-Gln-Leu-Glu-Phe-Lys-Val) which has alternate hydrphobic and polar (hydrophilic) residues will constitute Beta Strand. Valine and Isoleucine are Beta strand stabilizers. And due to the presence of alternating hydrphobic and hydrophilic residues, the one surface of Beta strand will be facing the interior (hydrophobic part) of the protein, and the other face (hydrophilic part) will face the surface exposed to water.

(3) The Sequence 1 looks as if it could form an amphipathic Alpha helix. It also has both polar and non polar residues in it and so will form a amphipathic helix. Also the Alpha helix stabilizers such as Glutamic acid (Glu), Alanine (Ala) and Methionine (Met) are also present in it.

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