I started a topic, in chemistry, about the impact of water on evolution at the nanoscale. This was a too large a topic since it parallels all of biology and evolution. That broader topic required I build background, which bogged down and detoured the discussion. I decided to narrow this topic down to just one thing, which is the impact of water and DNA.
To begin, the importance of water on the structure of DNA has been known since the Watson and Crick. Their original model of DNA was a triple helix bridged by Mg+2 ions, between the phosphate backbone on the three helixes.
Crick and Watson's first model was a triple helix with its bases on the outside of the molecule. The sugar-phosphate backbones ran down the centre, with the phosphate groups of each chain bound to one another by magnesium ions. Crick and Watson hoped that the low water content of the molecule would mean that magnesium ions were in abundance.
The model predicted repeat structure distances and showed promise. However, it did not equate properly to chemical analysis studies which showed that DNA contained far more water than assumed by Watson.
They had some difficulty making the model fit together, but found that it repeated its structure every 2.8 nanometres along its length. This was very encouraging, as both this 2.8 nanometre repeat and the helical structure would fit with Franklin's X-ray photograph. Crick and Watson needed to check their model accurately against the photograph, so they invited Wilkins and his colleagues from King's College to the Cavendish Laboratory.
When they arrived Franklin was still very dismissive of Crick's support for a helical structure. She pointed out that the proposed three-chained molecule couldn't exist, as any available magnesium ions would be tightly bound to water molecules. DNA actually contained ten times as many water molecules as Watson had thought. Franklin had stated the correct amount at her talk in London, but Watson had forgotten on the way back to Cambridge.
With the correct water content in mind, a more logical model eventually appears; double helix of base pairs.