alpha helix(redirected from a helix)
Also found in: Dictionary, Encyclopedia.
helix[he´liks] (pl. he´lices, helixes) (Gr.)
2. the superior and posterior free margin of the pinna of the ear.
α-helix (alpha helix) the complex structural arrangement of parts of protein molecules in which a single polypeptide chain forms a right-handed helix.
double helix (Watson-Crick helix) the structure of deoxyribonucleic acid (DNA), consisting of two coiled chains, each of which contains information completely specifying the other chain.
the helical form (commonly right-handed) present in many proteins, deduced by Pauling and Corey from x-ray diffraction studies of proteins such as α-keratin; the helix is stabilized by hydrogen bonds between, differet eupeptide bonds, for example, R1R2C = O and HN(R3)R4' groups, symbolized by the center dot in R1R2C = O · HN(R3)R4. In a true α helix, there are 3.6 amino acid residues per turn of the helix and an increase of 1.5 Ǻ per residue.
A secondary structure of proteins, characterized by a single, spiral chain of amino acids stabilized by hydrogen bonds.
al′pha-hel′i·cal (-hĕl′ĭ-kəl, -hē′lĭ-) adj.
alpha helixA specific form of folding of the polypeptide backbone in fibrous and globular proteins; right-handed corkscrew arrangement of a polypeptide chain is maintained by intrachain hydrogen bonding. The alpha helix is a major structural protein motif deduced by Pauling and Corey, and it occurs as bundles in keratin, myosin, fibrin and the epidermis.
alpha helixA coiled configuration of a POLYPEPTIDE chain found in many proteins. This is one of the commonest forms of secondary structure in proteins.
alpha helixa twisted polypeptide chain which forms a helical structure in many proteins, with 3.6 amino-acid residues per turn of the helix. Successive turns of the helix are linked by weak hydrogen bonds and the structure is much more stable than an untwisted polypeptide chain. Long-chain alpha-helix construction is characteristic of structural ‘fibrous’ proteins, found in hair, claws, fingernails, feathers, wool and horn. Proteins that are intracellular are usually of the ‘globular’ type with short segments of alpha helixes.
Pauling,Linus C., U.S. chemist and Nobel laureate, 1901-1994.
Pauling theory - a theory of narcosis pertaining to nonhydrogen-bonding agents. Synonym(s): hydrate microcrystal theory of anesthesia
Pauling-Corey helix - the helical form present in many proteins. Synonym(s): α helix