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:9/18/2014)... Americans across racial and ethnic groups describe losing ... their day-to-day life, more so than other conditions ... (57% of African-Americans, 49% of non-Hispanic whites, 43% ... which disease or ailment is the worst that ... African-Americans followed by AIDS/HIV. Hispanics and Asians ...
(Date:9/18/2014)... algal forests in the eastern Mediterranean Sea pose a ... distribution continues to expand as the climate warms, a ... of researchers led by Dr Adriana Vergs of UNSW ... for Advanced Studies in Spain, is published in the ... surveyed more than 1000 kilometres of coastline in Turkey ...
(Date:9/18/2014)... too stressed they are often grouchy, grumpy, nasty, distracted ... at EPFL have just highlighted a fundamental synaptic mechanism ... loss of social skills and cognitive impairment. When triggered ... in the brain. This was revealed by a work ... Sandi,s team went to look for answers in a ...
Breaking Biology News(10 mins):Americans rate losing eyesight as having greatest impact on their lives 2Americans rate losing eyesight as having greatest impact on their lives 3Tropical fish a threat to Mediterranean Sea ecosystems 2How stress tears us apart 2
... last couple decades have seen a virtual renaissance of ... functional magnetic resonance imaging (fMRI). Thanks to a ... scholars at Rutgers University will have the latest fMRI ... NSF has awarded Rutgers University in Newark a $1,820,000 ...
... natural organic pesticide for hundreds of years, is getting new ... pesticides. That,s the topic of a report in ACS, bi-weekly ... Cedric Briens and colleagues note that concerns about the health ... in some parts of the world. Scientists are looking for ...
... geoscientist Dr Veerle Huvenne of the United Kingdom,s National Oceanography ... 1.4 million Euros over five years to map complex habitats ... The European Research Council (ERC) ,Starting Grant, scheme aims ... their own research groups. The grants are highly competitive, and ...
Cached Biology News:$1,820,000 from NSF awarded to Rutgers-Newark to acquire fMRI dedicated to research 2
Other biology definitionOther Tags