|MoBio||Alpha Helix||Chapter 2|
An α helix has the following features:
Hydrogen bonds play a role in stabilizing the α helix conformation. However, the size and charges of sidechains are also important factors. Alanine has a greater propensity to form α helices than proline.
An α helix can be either right-handed or left-handed, as defined in the following figure.
The right-handed or left-handed helix may be distinguished by stretching out your thumb and curling the other four fingers. Imaging that in the above figure the helix is spiraling upward. Stretch your right thumb upward, then the other four fingers of the right hand will be able to curl in the same direction as each turn in the spiral. The same result can be obtained if you imagine that the helix is spiraling downward and point your thumb downward. The left hand works for the left-handed α helix.
Amphipathic α helix
In an amphipathic α helix, one side of the helix contains mainly hydrophilic amino acids and the other side contains mainly hydrophobic amino acids. The amino acid sequence of amphipathic α helix alternates between hydrophilic and hydrophobic residues every 3 to 4 residues, since the α helix makes a turn for every 3.6 residues. An example is shown below.