Alpha-helical regions of proteins can form amphipathic cylinders, where one side

Question

Alpha-helical regions of proteins can form amphipathic cylinders, where one side of the cylinder contains hydrophobic amino acids and the other side contains hydrophilic amino acids (i.e. located on opposite sides). If the hydrophilic and hydrophobic amino acids are intermixed, the helix is probably not amphipathic. The primary structures of three different 17-amino acid proteins (A, B, C) are listed below. The numbers at the head of the table correspond to the position of each amino acid in its respective protein. Only two of these proteins will form an alpha helix, the other will not. Which protein will not form an a-helix and why? Of the helical proteins, which will form an amphipathic helix? Use the helix wheel projection above to predict where the amino acids will line up in the helix Position

Explanation / Answer

B will make an alpha helix form.

Because the amino acids Asn, Asp, Gly, Pro, Ser intruppting the normal secondary structure. When they paired it creates more flexible and the polypeptides will fold back themselves.

C will form an amphipathic helix.

Because the aminoacid sequence of amphipathihelix is alternate between the every 3 -4 residues of hydrophilic and hydrophobic.

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