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


'"/>


(Date:10/16/2014)... be cultivated efficiently, they are anything but sustainable: ... monoculture cultivation is becoming increasingly evident. Despite their ... and are regarded as the sole possibility of ... wrongfully, finds Bernhard Schmid, an ecology professor at ... form of agriculture and forestry. After all, a ...
(Date:10/15/2014)... As our ability to assess the pandemic risk from ... developments, we must not allow ourselves to become complacent ... an international consortium of scientists. , Influenza pandemics arise ... have yet to develop widespread immunity – spreads in ... in the past 100 years, the worst of which ...
(Date:10/15/2014)... NXT-ID, Inc. (NASDAQ: NXTD and NXTDW) ... growing mobile commerce market releases photos and video of the recent ... October 13 th . Gino Pereira , ... angel investor Mr. Chad A. Verdi rang the bell.  ... his investors and employees "for their work and dedication in bringing ...
Breaking Biology News(10 mins):Plant communities produce greater yield than monocultures 2Plant communities produce greater yield than monocultures 3Scientists 'must not become complacent' when assessing pandemic threat from flu viruses 2Photo Release: NXT-ID Inc. Rings Opening Bell of the NASDAQ Stock Market October 13th 2Photo Release: NXT-ID Inc. Rings Opening Bell of the NASDAQ Stock Market October 13th 3
... E or a combination of the supplements had a similar ... supplements, according to data from a randomized controlled trial in ... the National Cancer Institute. Epidemiological studies have suggested ... and thus antioxidants, may have a lower risk of cancer. ...
... has the honour of becoming the first student from ... competition that pitted engineering students and young professionals from ... the Institution of Engineering and Technology (IET), UK, the ... Mechanical & Aerospace Engineering beat three other contestants in ...
... Is Sensitive to Irradiation Researchers led by ... irradiation damages fat tissue. They report their findings in ... of Pathology . Radiation therapy directed ... of tissues such as fat tissue has often been ...
Cached Biology News:Vitamins C and E and beta carotene again fail to reduce cancer risk in randomized controlled trial 2NTU undergrad is first Singapore champion of an internationally acclaimed engineering competition 2NTU undergrad is first Singapore champion of an internationally acclaimed engineering competition 3Tips from the American Journal of Pathology 2Tips from the American Journal of Pathology 3Tips from the American Journal of Pathology 4Tips from the American Journal of Pathology 5
Other biology definitionOther Tags