Summary
Designed in MinecraftEdu

Instructions
Print 4 of the DNA Core and one of each of the A, T, C and G. This will allow you to create the model similar to the red design I have printed. To use with students I plan on printing the core in black or white and then printing each of the 4 nucleotides in different colours. When I do this I will upload a picture.
Note this model follows the base pairing rule of DNA, only A and T will join together and so will C and G.
I designed each Minecraft block to be 0.2mm, so if you can, print this with a layer height of 0.2mm. I also rotated the DNA core so that the site for joining the nucleotide was up, this also minimises the support required, I will try to figure a way to do this to the stl file and update soon.
If you would like to make a larger model, you can, it should be continuous, just print enough DNA Cores and then enough pairs of A and T and C and G. I will design a stand and add it here soon.