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He discovered that the genetic material found inside white blood cells nuclei had an acid, and he called it nuclein. -
He determined the main components of the DNA, adenine, guanine, thymine, cytosine, and deoxyribose phosphate. Another important discovery he made was defining phosphate-units-base called nucleotides. -
In 1910, Leven's continued studying tirelessly to learn more about DNA components and structure. So he proposed the tetranucleotide theory, that affirmed that there were four nucleotides per molecule, and also that DNA couldn't contain our genetic code because its chemical composition was too simple to save it. -
He made an experiment with the Streptococcus pneumoniae. He used 2 strains of it, the Type S (Virulent and deadly) and Type R (Non-virulent but harmful). He learned that smooth colonies secrete a capsule that kills the mice, while rough colonies didn't secrete it. Yet, he discovered that heat-killed smooth strain didn't kill the rat, while heat-killed smooth strain with rough strain killed it. He reported its studies and were the first widely accepted demonstrations of bacterial transformation. -
These scientists took live Type R and heat-treated Type S and mixed it with one of two enzymes: proteases (which destroy proteins) and DNAse (which destroys DNA). They discovered that Type R (non-virulent) mixed with heat-killed smooth and the protease the mouse's dies. While, when mixed with the DNAse, the mouse lives. -
They wrote a paper saying that DNA was a double helix structure with sugars and phosphates at the centre and the nucleobases distributed on the edge of it facing the outside. This theory has been proved to be wrong because posterior experiments in the lab concluded it made no chemical sense. -
He created universal rules of DNA, establishing that DNA is a sort of patterns made of Adenine that combined with Thymine and Cytosine that combined with Guanine. These rules were later very useful to understand the hydrogen connections between the bases of the DNA. -
He did an experiment by using paper chromatography and UV spectroscopy and examined the abundance of the nucleobases. When doing this, he discovered that the amounts of Adenine were the same as the amounts of Thymine, and the amounts of Cytosine were the same as the amounts of Guanine. Always, and in every specie. -
They proposed the theory of a triple-helix structure for DNA. But was later proved wrong, because DNA would break and it would create a genetic instability. -
They did an experiment that let them conclude that DNA was the one that contained the genetic material, not the protein. The proteins made a protective shield around the bacteriophage, but the internal DNA is who conferred its unique ability to produce progeny inside bacteria. -
She discovered that DNA was a tridimensional structure, by an X-Ray image called "Photo 51".
Photo 51 was an example of a DNA B from (wet form, as DNA exists in cells). While the A form (dry form) is quite different on the X-Ray's. -
Finally, on April 25 of 1953, Watson J.D. and Crick F.H.C. created a 3D model of the DNA as we know it nowadays.