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- Friedrich Miescher Friedrich, isolated the genetic material from white blood cell nuclei, and he observed that it had an acidic nature, for these reason he called it nuclein. He didn't know it, but he had discovered a molecule with genetic information, that in the future would be very important for the discoveries.
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- Phoebus Levene. Discovered all the components of the DNA, and defined the unit, including the sugar, the phosphate, and the base which called a nucleotide. The problem is that he didn't understand well the structure, because he thought that it was organized in tetrades. He said there were four nucleotides per molecule, and that it was to simple structure that it couldn't possible.
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- Frederick Griffith Studies the epidemiology and the pathology of 2 strains of Streptococcus pneumonia: the type S (virulent) and the type R (non-virulent). He arrives to the conclusion that the DNA is the responsible for the transformation, because they can change other bacteria if you can mix the type S died (that no cause disease) with the type R alive (that cause disease), the bacteria R transforms to the type S. And this change is produced with the DNA (although Griffith didn't know it).
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- Oswald Avery.
- Colin MacLeod.
- Maclyn McCarty. They took live R and heat-treated S and mixed it with one of two enzymes. One group was mixed with proteases, that destroys proteins, and the other group mixed with DNase witch destroys DNA. So, they mixed the non-virulent strain with the virulent, one group mixed with the proteases, and the mice died. The other group mixed with the DNase, and the mice lives. Arrive to the conclusion that DNA are the responsible for transformation.
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- Watson and Crick They wrote a paper in which they described DNA as a double helix structure, formed by sugars and phosphates at the center, and the nucleobases facing the outside. Later, confirmed that this model was incorrect, for chemical sense. All the negative charge in the phosphates inside the structure, couldn't be there, because the most probably think are that arrive one moment that the ADN exploded with negative charges.
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- Erwin Chargaff. Examine the abundance of nucleobases. He looked at different organisms, and he measured the quantities of the four bases: the adenine, the thymine, the cytosine and the guanine. He looked at some different organisms, and she discovered that in all of them have the same quantity of the adenine and thymine, and cytosine and guanine (are always in balance). Also, the humans, have the same result. This helped in the development of the double helix structure (A = T and C = G)
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- Alfred Hershey
- Martha Chase Bacteriophages are viruses that infect bacteria, that are made of DNA or RNA, and proteins. In the experiment, marked the ADN with radioactive phosphorus (³²P) and the proteins with radioactive sulfur (³⁵S). Permit that viruses infect the bacteria, and next, use the centrifugation to separate it and see where enter the radioactive material. Conclude, that the ADN carries the genetic information, because the ADN enter to the bacteria and the proteins not.
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- Rosalind Franklin Rosalind took a lot of photographs of the B form of DNA. She figured out how to see the wet form, the form that exist in cells. The most famous photo is called photo 51, in here you can see very clear the X in the middle, that is the sign of a double helix. Rosalind, didn't want to show the photo until was sure of her calculations. But, Maurice Wilkings take the photo of Rosalind's desk and send it to Watson and Crick.
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When the photo arrives to her, they see quickly the error, her firts theory was backward. They reconstructed a new model based on Rosalind's image. When the final model was finished, the journal "Nature", published three articles, the first one was for Watson and Crick, the second one, was for Stokes and Wilkings, and the last one was for Rosalind Franklin. A lot of people things that the responsible for the discovered are Watson and Crick, and that's wrong, the original responsible is Rosalind. -
- Linus Pauling He was to discovert the structure of the alpha helixes, and elaborate the triple helix model, with the phosphates and sugar on the inside, and the nucleobases in the outside (the same as the double helix theory). He was possibly looking at x-ray crystallography images, that are a mixture that the two models of DNA (A and B form) that mixed are similar to a triple helix. But, this theory, be incorrect again, but, also help to the next discoveries.