Researchers have described the“binary patterning†of polar and nonpolar amino acids in thesequences of proteins. In their code, polar and charged residueslike D, N, E, Q, K, H, and R are represented as open circles (â—‹)and nonpolar residues like F, L, I, M, and V as closed circles (â—).Thus, a polypeptide with the sequence asp-ile-his-phe-gln would berepresented as â—‹â—â—‹â—â—‹. Researchers analyzed the binary patterns ofisolated secondary structure elements (short pieces) from nativeproteins. A sequence with the pattern â—‹â—â—â—‹â—‹â—â—â—‹â—‹â—â—â—‹ forms anamphipathic alpha helix that has a nonpolar face and a polar face.A sequence with the pattern â—‹â—â—‹â—â—‹â— forms an amphipathic betastrand. Explain these observations by discussing the structures ofhelices and sheets.
