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glossary:alpha_helix [2008/08/12 15:13]
glossary:alpha_helix [2008/09/17 08:49] (current)
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 +======  Alpha Helix  =======
 +The alpha helix is the most abundant type of secondary structure in proteins and has been extensively documented. 
 +In brief, alpha helices are formed from stretches of consecutive amino acid residues
 +with phi and psi angle pairs which correspond to the bottom left quadrant of the [[glossary:ramachandran_plot | Ramachandran Plot]].
 +The mean phi and psi angles for alpha helices found in proteins are -62 degrees and -41 degrees,
 +respectively. The alpha
 +helix has 3.6 residues per turn, with a [[glossary:hydrogen_bond | hydrogen bond]] between the CO of residue
 +n and the NH of residue n +4. The closed loop formed by one of these
 +hydrogen bonds and the intervening stretch of backbone contains 13 atoms (including the hydrogen).
 +Hence the nomenclature for an alpha helix is 3.6(13)-helix, where the 3.6 is the
 +number of residues per turn and 13 is the number of atoms in the
 +hydrogen bonded [[glossary:loop |loop]].
 +Some alpha helices are curved or show distinct kinks, for example those caused by
 +the presence of proline residues. The example shown is a enterotoxin (CATH domain ID 1tiiC00).
 +===== References =====