And we'll discuss what these nitrogenous bases are in just a moment. These bases are not part of that backbone of the nucleic acid because unlike these, the bases do actually change as we go from one nucleotide to another nucleotide. So the backbone that does not consist of these bases, but consists of these repeating units, does not change and remains constant throughout that entire nucleic acid. Now, what else can we say about this backbone? So notice that because the backbone contains these repeating phosphate groups and because the phosphate groups carries a negative charge, that makes this part of the backbone hydrophilic. So water loving, that's because we have a dipole moment that exists as a result of the charge that is delocalized among these two oxygen atoms within our phosphate group.