Navigation Links
Alpha helix


In proteins, the α helix is a major structural motif in secondary structure. It was first postulated by Linus Pauling, Robert Corey , and Herman Branson in 1951 based on the known crystal structures of amino acids and peptides and Pauling's prediction of planar peptide bonds.

The amino acids in an α helix are arranged in a helical structure, about 5 wide. Each amino acid results in a 100 turn in the helix, and corresponds to a translation of 1.5 along the helical axis. The helix is tightly packed; there is almost no free space within the helix. All amino acid side-chains are arranged at the outside of the helix. The N-H group of amino acid (n) can establish a hydrogen bond with the C=O group of amino acid (n+4).

Short polypeptides usually are not able to adopt the alpha helical structure, since the entropic cost associated with the folding of the polypeptide chain is too high. Some amino acids (called helix breakers) like proline will disrupt the helical structure.

Ordinarily, a helix has a buildup of positive charge at the N-terminal end and negative charge at the C-terminal end which is a destabilizing influence. As a result, α helices are often capped at the N-terminal end by a negatively charged amino acid (like glutamic acid) in order to stabilise the helix dipole. Less common (and less effective) is C-terminal capping with a positively charged protein like lysine.

α helices have particular significance in DNA binding motifs, including helix-turn-helix motifs, leucine zipper motifs and zinc finger motifs. This is because of the structural coincidence of the α helix diameter of 12 being the same as the width of the major groove in B-form DNA.

α helices are one of the basic structural elements in proteins, together with beta sheets.

The peptide backbone of an α helix has 3.6 amino acids per turn.

See also: tertiary structure -- β sheet -- collagen helix

References


'"/>


See more about: Alpha helix

TAG: Alpha helix
(Date:11/19/2009)... at Louisiana Tech University has found that a nat...erbicide against giant salvinia. , Giant salvini...block all sunlight penetration into bodies of wate...ions, it,s been reported that giant salvinia can d...lker, professor of biological sciences at Louisian...
(Date:11/19/2009)...has identified thousands of diverse genes in genet...chniques may allow breeders and researchers to use...ts and create new varieties that were not easily p...e of Science , the researchers, whose senior and ...irst map of haplotypes sets of closely linked gen...
(Date:11/19/2009)...echnique developed by researchers at the Universit...or specific gene-regulatory regions without requir...factors. The technique has been experimentally val...genome. , "Our statistical approach is more widel...lly useful for investigating gene regulatory netwo...
Breaking Biology News(10 mins):Microorganism may provide key to combating giant salvinia throughout Louisiana 2New map of variation in maize genetics holds promise for developing new varieties 2Technique finds gene regulatory sites without knowledge of regulators 2TSI Healthcare Commends Efforts of New Healthcare IT Plan 49412 1TSI Healthcare Commends Efforts of New Healthcare IT Plan 49412 2TSI Healthcare Commends Efforts of New Healthcare IT Plan 49412 3Cox Movies Under the Moon 28R 29 Offers Big Screen Hits Under the Stars 49409 1Cox Movies Under the Moon 28R 29 Offers Big Screen Hits Under the Stars 49409 2Cox Movies Under the Moon 28R 29 Offers Big Screen Hits Under the Stars 49409 3Study Finds Possible Genetic Indicator of Colorectal Cancer 49406 1Study Finds Possible Genetic Indicator of Colorectal Cancer 49406 2
...birthday, according to new infant mortality statis...Health Statistics (NCHS). , The infant mortality r...er increasing in 2002 for the first time since 195...deaths for every 1,000 live births, which was stat...-thirds of all infant deaths occurred within the f...
... the amazing repertoire of carbon nanotubes -- the...s. , Nanotubes, tiny hollow carbon filaments about...are already famed as one of the most versatile mat...as steel and one-sixth as dense, able to conduct e... silicon in semiconductor chips, carbon nanotubes ...
...es it do? It stops eating. Humans should be so luc...ten head for the refrigerator, producing unhealthy...ormally solitary, are placed in a group-living sit...e Center for Behavioral Neuroscience at Georgia St...uman stress-induced obesity. They want to begin un...
Other Biology News:US infant mortality rate fails to improve 2Nanotubes used for first time to send signals to nerve cells 2Just like us, social stress prompts hamsters to overeat, gain weight 2Just like us, social stress prompts hamsters to overeat, gain weight 3Just like us, social stress prompts hamsters to overeat, gain weight 4
Other biology definitionOther TagsVowsUTIsUTIs