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| + | {{tag>alpha}} | ||
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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). | ||
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| + | {{cath:feature>1tiiC00}} | ||
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| + | ===== References ===== | ||
| + | |||
| + | {{pubmed>long:3418712}} | ||
| + | {{pubmed>long:14816373}} | ||
| + | {{pubmed>long:642001}} | ||
| + | {{pubmed>long:3225849}} | ||
