helix, pl. helices (he´liks, hel´i-sez)

1. [NA] The margin of the auricle; a folded rim of cartilage forming the upper part of the anterior, the superior, and the greater part of the posterior edges of the auricle. 2. A line in the shape of a coil (or a spring, or the threads on a bolt), each point being equidistant from a straight line that is the axis of the cylinder in which each point of the h. lies; often, mistakenly, applied to a spiral (the threads on a screw). [L. fr. G. helix, a coil]
310 h. a type of right-handed h. found in small pieces in a number of proteins; has three amino acid residues per turn.
3.613 h. a h
a h. the helical (commonly right-handed) form present in many proteins, deduced by Pauling and Corey from x-ray diffraction studies of proteins such as a-keratin; the h. is stabilized by hydrogen bonds between, e.g., C=O and HN groups (symbolized by the center dot in CO. HN ) of different eupeptide bonds. In a true a h., there are 3.6 amino acid residues per turn of the h.3.613 h., Pauling-Corey h;
collagen h. an extended left-handed h. resulting from the high levels of glycine, l-proline, and l-hydroxyproline present in the collagens. There are 3.3 amino acids per turn of the helix. Three of those left-handed helices form a triple superhelix that is right-handed.
DNA h. Watson-Crick h
double h. Watson-Crick h
pi h. a rare right-handed h. found only in small portions of certain proteins. Stabilized by similar hydrogen bonds as in an a h.; there are 4.3 amino acid residues per turn of the h.
Pauling-Corey h. a h
triple h. the superhelix formed (right-handed) from three individual collagen helices (each being left-handed).
twin h. Watson-Crick h
Watson-Crick h. the helical structure assumed by two strands of deoxyribonucleic acid, held together throughout their length by hydrogen bonds between bases on opposite strands, referred to as Watson-Crick base pairing. See base pair.DNA h., double h., twin h;


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