Alpha helix

"The alpha helix is one of the most common secondary structures in proteins. Amino acid side chains project outwards from the polypeptide backbone that forms the core of the helix. The chain is stabilized in this conformation by hydrogen bonds between the backbone amino group of one amino acid and the backbone carbonyl group of another amino acid that is four positions away. These interactions do not involve side chains. Thus many different sequences can adopt an a helical structure. Alpha helices are regular cylindrical structures. One full turn occurs every 3.6 residues and extends the length of the helix by approximately 0.5 nm. Secondary structures are often represented in cartoon form to clarify the underlying structure of a protein. In this representation, the twisted 3D ribbon follows the path of the peptide backbone." Essential Cell Biology, Second Edition by Alberts, Bray, Hopkin, Johnson, Lewis, Raff, Roberts, Walter copyright 2004 by Garland Science Publishing