In the figure on the right, we imagine a 2D polypeptide composed of a helix-turn-helix motif. It has two helices, each with 2 faces (1,2 and 3,4). If we think of the resude side chains on each face as being either all hydrophobic (H) or all hydrophillic (P), there are 16 possible sequences (2^3). Similar to Kell Dill's HP model, we will calculte the energy of each state by applying a 1e penalty for each hydrophobic face in contact with the solvent or a polar face.