A ground-state conformation in the 2D HP model. The grid points and lines represent the 2D square lattice this conformation is embedded upon. Filled, black circles represent hydrophobic residues while unfilled circles represent polar residues. The conformation above yields an optimal energy score in the HP model of -2. The two hydrophobic contacts contributing to the score are between residues 4 and 13 and between residues 5 and 12.