Computed biological hydrophobicity scale using a classical view of the membrane. (A) A model peptide with an arginine at the central position (green) is shown spanning a low-dielectric region representing the membrane. Helical segments with this geometry were used to produce the bar graph in B. (B) Insertion energies for 19 of the 20 naturally occurring amino acids. Amino acids are ordered according to the translocon scale (Hessa et al., 2005a). All molecular drawings were rendered using VMD (Humphrey et al., 1996).