The presence of these structures can be identified on hydrophilicity or hydrophobicity plots by a stretch of 20 positive values on the Kyte–Doolittle scale. A double minimum at 208 and 222 nanometers in circular dichroism spectroscopy is used to identify these structures. These structures have square-like cross sections that allow them to be differentiated from similar structures named for “310” and pi. Two of these structures are dimerized in the DNA-binding leucine zipper motif. (*) Glycine and proline are called “breakers” of these structures. A diagonal cluster on Ramachandran plots around dihedral angles of −60 (“negative 60”) and −45 (“negative 45”) degrees identifies these structures. Hydrogen bonds stabilize the 3.6 residues per turn characteristic of these structures. For 10 points, name this coiled secondary structure motif in proteins that is more common than beta sheets. ■END■
ANSWER: alpha helix [or alpha helices; prompt on helix or helices or coils]
<SM, Chemistry>
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