And on the outside portion, because these phosphate groups essentially point on the outside and they contain charge the exterior of the DNA of the double helix is negatively charged and it is hydrophilic while the interior is hydrophobic because it consists of these nonpolar nitrogenous bases. So DNA exists predominantly as a double helix. And what that means is we have these two strands of DNA that essentially run an antiparallel direction and they interact via different types of non covalent interactions. So hydrogen bonds, London dispersion forces and so forth. The interior is hydrophobic, just like in proteins and the exterior is hydrophilic once again just like in proteins. And these two strands are complementary with respect to one another.