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--- glossary:alpha_helix [2008/08/11 08:48] – cuff
+++ glossary:alpha_helix [2008/09/17 07:49] (current) – garner
@@ Line 1: / Line 1: @@
+{{tag>alpha}}
+======  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).
+{{cath:feature>1tiiC00}}
+===== References =====
+{{pubmed>long:3418712}}
+{{pubmed>long:14816373}}
+{{pubmed>long:642001}}
+{{pubmed>long:3225849}}

CATH