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Alpha helix

Definition(s)

A right-handed spiral conformation; the a-helix has a pitch of 5.4 A and has 3.6 amino acid residues per turn; every main chain C=O and N-H group is hydrogen-bonded to a peptide bond 4 residues away; the peptide planes are roughly parallel with the helix axis and the dipoles within the helix are aligned, i.e. all C=O groups point in the same direction and all N-H groups point the other way; side chains point outward from helix axis and are generally oriented towards its amino-terminal end.: Definition from: Unified Medical Language System (NCI Thesaurus) at the National Library of Medicine


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