Akademik

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. [L. fr. G. h., 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. SYN: α h..

- α 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 α-keratin; the h. is stabilized by hydrogen bonds between, e.g., R₂C=O and HNR₂′ groups (symbolized by the center dot in R₂CO HNR₂′) of different eupeptide bonds. In a true α h., there are 3.6 amino acid residues per turn of the h. and a rise of 1.5 Å per residue. SYN: 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 acid s per turn of the h.. Three of those left-handed helices form a triple superhelix that is right-handed.

- DNA h. SYN: Watson-Crick h..

- double h. SYN: Watson-Crick h..

- π h. a rare right-handed h. found only in small portions of certain proteins. Stabilized by similar hydrogen bonds as in an α h.; there are 4.3 amino acid residues per turn of this h..

- Pauling-Corey h. SYN: α h..

- triple h. the superhelix formed (right-handed) from three individual collagen helices (each being left-handed).

- twin h. SYN: 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. SYN: DNA h., double h., twin h..

he·lix 'hē-liks n, pl he·li·ces 'hel-ə-.sēz, 'hē-lə- also he·lix·es 'hē-lik-səz

1) the incurved rim of the external ear

2) a curve traced on a cylinder by the rotation of a point crossing its right sections at a constant oblique angle broadly SPIRAL (2) see ALPHA-HELIX, DOUBLE HELIX

the outer curved fleshy ridge of the pinna of the outer ear.