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After discovering that nucleic acids were stored in the chromosomes. After that, he did experiments, and arrived at the conclusion that the four base molecules, (adenine, guanine, cytosine, and thymine) occur in approximately equal ratios. And he supposed that the nucleic acid had a repeating tetrameter. However, he was wrong. -
Phoebus Levene, determined the components of DNA, wich were Adenine, Guanine, thymine, cytosine, deoxyribose phosphate. He also defined phosphate-sugas-base units, called nucleotides. -
This was the first experiment suggesting that bacteria are capable of transferring genetical information, through a process known as transformation.
This experiment was made to search a cure for pneumonia, which was a serious cause of death in Spain after WWI. He used pneumococcus, and injected into a mouse. -
They determined what really caused the transformation.
They used the live rough pneumococcus, and mixed with the heat-theated, and then in a group of mice mixed proteases, which destroy proteins, and in the other the mixed DNAse, which destroy DNA, and the results were that the groups with DNAse survived, while the other died, confirming that the DNA was responsible for transformation. -
For this experiment, Hershey and Chase used a Bacteriophage, a virus that infects bacteria.
They used radioactive material (35S), to see what the movement of the protein capsule, and then they also used a radioactive material(32P) to see the movement of DNA. After letting the bacteriophage infect the other bacteria, and then they separated what was in the bacteria by centrifugation. They arrived at the conclusion that the DNA was the genetic material, not the protein -
After all the researches and experiments, the scientists arrived at the conclusion that:
- The backbone is made of sugar and phosphate
- There are hydrogen bonds between the nucleobases
- The sequence of nucleobases codifies the amino acid sequence of a protein
- Strings of base pairs that code for a product are called genes -
James Watson and Francis Crick published their theory of the structure of the DNA, they said that DNA must be shaped like a double helix, and every upright pole, must have a backbone of alternating sugar and phosphate groups. Each DNA base (adenine, cytosine, guanine, thymine) is attached to the backbones, and these bases form the rungs. -
Erwin Chargaff used paper chromatography and UV spectroscopy, to examine the abundance of nucleobases. For his experiment, he started looking to organisms, first an octopus, then a sea urchin, a rat, a grasshopper, and a human. After making a comparison, he saw that there was a balance between Adenine and Thymine, and Cytosine and Guanine. -
In February 1953, Linus Pauling and Robert Brainard proposed a structure for deoxyribonucleic acid, or usually known as DNA. In their article, they suggest a model for nucleic acids, including DNA, that consisted of three nucleic acid strands wound together in a triple helix. After a short time, scientists arrived at the conclusion that genes, the biological factors that control how organisms develop, contained DNA. Though, they proved that the theory of Linus and Robert was incorrect.