I loved the design made by mkuiper but I loathe printing support. I split the models in such a way that they can be printed without support. Simply glue them together afterwards (super glue works best I've found).

Adenine, Cytosine, Guanine and Thymine were easy to alter because the molecule is already symmetrical along a plane. The backbone was very hard to find a suitable plane for along which it could be split such that it would print without support. I've found one that works but it relies on solid cooling to print a few pretty steep overhangs.

Play with the orientation of the backbone with respect to your part cooling fan to achieve the best results (steep overhangs facing the direction of the airflow).

In addition I've also noticed that the stand seems to be split up into parts unnecessarily. I've combined the 3 parts that make up the bottom parts of the stand into one model. I've also split up the grip so that it can also be printed without the need for support. Maximum overhang angle for the grip is aprox. 55 degrees.

I've included the other parts of the stand for completeness sake.

The small molecules that go on the ends of the helix you only need 4 of, so I just printed those with support material because it's not worth the effort of glueing them back together.

Creality

Use super glue to attach the halves together, make sure to sufficiently clamp the backbone pieces or they will split during assembly of the model.