And so on this strand, we have one nucleotide a second nucleotide, a third nucleotide. And on the other strand, we also have this one nucleotide, second nucleotide, a third nucleotide. And what it means for these to be complementary is that these bases here are complementary meaning that they can form an optimal arrangement of bonds. So these bonds here are basically the hydrogen bonds that hold our bases together. So what holds this entire double helix in DNA are the hydrogen bonds as well as Van der Vall forces and the hydrophobic effect. So in the inside portion of our DNA we have these hydrophobic regions.