 The main attraction in investigating alpha helix formation is that one encounters many of the features of protein folding but in their simplest version.Most of the helix–coil models contain parameters for the likelihood of helix nucleation from a coil region, and helix propagation along the sequence once nucleated; because polypeptides are directional and have distinct N-terminal and C-terminal ends, propagation parameters may differ in each direction.The two states are

Common transition models include the Zimm–Bragg model and the Lifson–Roig model, and their extensions and variations.