 The other interesting part that Watson and Crick found out is that they were able to explain the specific pairing that A binds to T and G binds to C and that is based on the specific number of hydrogen bonds that you can form between the bases here in the middle. Now under some conditions you can actually have different types of base pairing but this is the most stable base pairing and then we have one more of these things it just makes sense. Everything we throw at the model to test it comes back just confirming the model even more and that is why they got a nature paper of this and a Nobel Prize in the 1960s.