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:10/30/2014)... researchers have developed a suite of technologies that can ... which has applications in everything from search and rescue ... developed a platform for computer-mediated communication between humans and ... interpreting dogs, behavioral signals and sending them clear and ... assistant professor of computer science at NC State and ...
(Date:10/29/2014)... Cancer suffers who lose their hair as a consequence ... that will improve the scalp cooling technology that prevents ... and is being pioneered by global scalp cooling manufacturing ... with the biology department of the University of Huddersfield. ... Omar Hussain, who has a background in the pharmacology ...
(Date:10/29/2014)... have been blamed for increasing the risk of ... family history of schizophrenia, are widely accepted. Others, ... a parasite transmitted by soil, undercooked meat and ... A new study by Gary Smith, professor of ... Pennsylvania,s School of Veterinary Medicine, used epidemiological modeling ...
Breaking Biology News(10 mins):New tech aims to improve communication between dogs and humans 2New technology on the way to aid cancer suffers who lose their hair after chemotherapy 2Penn vet professor investigates parasite-schizophrenia connection 2Penn vet professor investigates parasite-schizophrenia connection 3
... producing proteins that moonlight, having different roles at different ... killed. The moonlighting activity of one enzyme from the ... of broad-spectrum antibiotics, according to a paper published in ... "Glutamate racemase, or MurI, is an enzyme ...
... many recent reports documenting the therapeutic efficacy of short ... may actually be describing non-specific therapeutic effects related to ... according to a paper in the September 2008 issue ... , a peer-reviewed journal published by Mary Ann Liebert, ...
... NY, Sept. 2, 2008) People concerned about the ... families and communities will have a unique opportunity to ... about the causes, symptoms and progression of such illnesses ... learn about current and potential treatments. In an ...
Cached Biology News:Energy-saving bacteria resist antibiotics 2Previous claims of siRNA therapeutic effects called into question by report in human gene therapy 2Healthy Minds Across America features 48 public forums on mental health research, Sept. 14 2Healthy Minds Across America features 48 public forums on mental health research, Sept. 14 3
Other biology definitionOther Tags