Q: Explain why, for folded proteins, the number of hydrophobic residues divided by the number of hydrophilic residues is the same when proteins are modeled in two dimensions, as it is when proteins are modeled in three dimensions.

A: Hydrophilic residues incline to be on the surface of the protein and hydrophobic residues inside. The ratio of the number of hydrophilic residues to hydrophobic residues is therefore proportional to the surface (L²) volume (L³) ratio. This ratio is the same for 2D and 3D.