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Miescher isolated a substance from white blood cell nuclei he called “nuclein” (later known as DNA). This experiment was crucial to make way for the other scientist to discover even more about genetics. -
Shortly after the discovery of the nucleic acids, Levene discovered and determined the components of DNA, these being:- Adenine
- Guanine
- Thymine
- Cytosine
- Deoxyribose phosphate
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After discovering nucleotides, Phoebus Levene proposed that DNA was made of repeating units of four nucleotides over and over again, and he thought they were organised in tetrades, which wasn't correct. Other scientists thought that DNA couldn't store genetic information because the theory he presented was pretty simple. -
Griffith studied bacteria (Streptococcus pneumoniae) that were either soft (made mice sick) or rough (harmless).- Mice died with soft
- Lived with rough
- Lived with dead soft. (heat-killed)
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This is one of the most important journals of medicine at the moment, and they stated that DNA, rather than protein, may be the hereditary material of bacteria, and perhaps in higher organisms as well. -
They wanted to determine the cause of the transformation of the bacteria that Griffith worked with, and they did! They took the alive rough bacteria and the heat-killed soft one, and mixed them with two different enzymes:
1. Protease -- Kills protein
2. DNase -- Kills DNA One group of mice got the one that was mixed with protease, and died, and the other group got the one that had DNase in it, and lived. That means DNA was responsible for the transformation! -
In 1951, Watson and Crick wrote a paper in which they described DNA as a double helix, with sugars and phosphates at the center, while the nucleobases were facing the outside. This model they created was quickly demonstrated to be incorrect because again, it made no chemical sense. -
James Dewey Watson and Francis Crick characterized DNA as a double helix, with sugars and phosphates located in the cente, while the nucleotides are positioned outward. This was wrong, as it didn't make any chemical sense to have so many negatively charged phosphates; it could explode. -
Bacteriophages are viruses that purposely target and infect bacteria. In the most cases, they are made of DNA, but there are a few that are made of RNA. The rest of it is just proteins, that are considered the "packaging". They did the test to know if it was the DNA or the proteins who carried the genetic information. -
His experiment consisted on testing in different animals, to see if the amount of every component was the same or different, and discovered that every species that he experimented with had the equal amount of adenine and thymine, and the same happened with guanine and cytosine. -
These rules said before became well-known as "Chargaff's rules". These consisted about the amounts of adenine and thymine, and of cytosine and guanine, were always in balance. It's a shame that he shared this information with two other scientists called Watson and Crick, to later steal his recognition and nobel prizes. -
To know if it was the DNA or the protein that carried the genetic information. They did an experiment where they exposed proteins with radioactive sulphur (35S) and DNA with radioactive phosphorus (32P), while they were carried inside a phage. When the phages infected the bacteria, only the radioactive DNA was able to infect the pellet, when the protein couldn't. They concluded that DNA was the one who carried the genetic information, while the protein was a sort of "packaging". -
Linus Paulingactually discovered the structure of alpha helices and beta sheets in proteins. From the other hand, based on x-ray crystallography images of both the a and b model of DNA, he proposed a triple helix design and structure for DNA. Again, with phosphates and sugars on the inside and nucleobases on the outside. Unfortunately, it turned to be proved incorrect again. -
This all started when Wilkins stole the most famous picture of DNA inside a cell from a woman who worked in crystallography. When he discussed it with his companions, they exactly knew what was happening, and it resulted that the correct structure was actually theirs, but upside down. This is the modern DNA model and structure, and after many attempts from other scientists, they finally managed to work it out. -
As I said before, Wilkins stole a precious picture from a woman who worked as a crystallographer. She discovered the wet form of DNA, called form B. They stole all of her recognisement, winning awards, while they never did anything to deserve it. -
DNA is basically the instruction book for all living things. It tells our cells how to work and what we look like. Because of its double helix shape, DNA can copy itself, so information gets passed on from parents to children. The order of its “letters” (A, T, C, G) acts like a code for making proteins, which keep us alive and give us our traits. Sometimes DNA changes, which can cause problems, but it’s also what makes us all different and drives evolution.