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..Gregor Mendel
Gregor Mendel
Gregor Mendel the
"Father of Genetics" performed an experiement in 1857 that led
to increased interest in the study of genetics. Mendel who became a
monk of the Roman Catholic church in 1843, studied at the University of
Vienna where he mastered mathematics, and then later performed many
scientific experiments. The greatest experiment that Mendel
performed involved growing thousands of pea plants for 8 years. He
was forced to give up his experiment when he became abbot of the monastery
because of the political problems of the time. He died in 1884, but
has been remembered for the great contribution to science that he made.
To learn about his experiment and what it led to read: Genetics.
Frederick Griffith
In 1928 a scientist named Frederick Griffith was working on a project that enabled others to point out that DNA was the molecule of inheritance. Griffith's experiment involved mice and two types of pneumonia, a virulent and a non-virulent kind. He injected the virulent pneumonia into a mouse and the mouse died. Next he injected the non-virulent pneumonia into a mouse and the mouse continued to live. After this, he heated up the virulent disease to kill it and then injected it into a mouse. The mouse lived on. Last he injected non-virulent pneumonia and virulent pneumonia, that had been heated and killed, into a mouse. This mouse died.Why? Griffith thought that the killed virulent bacteria had passed on a characteristic to the non-virulent one to make it virulent. He thought that this characteristic was in the inheritance molecule. This passing on of the inheritance molecule was what he called transformation.
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Died | Mouse with virulent pneumonia | Mouse with heated virulent pneumonia and non-virulent pneumonia mixed together |
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Lived | Mouse with non-virulent pneumonia | Mouse with heated, killed virulent pneumonia |
Oswald Avery
Fourteen years later a scientist named Oswald Avery continued with Griffith’s experiment to see what the inheritance molecule was. In this experiment he destroyed the lipids, ribonucleic acids, carbohydrates, and proteins of the virulent pneumonia. Transformation still occurred after this. Next he destroyed the deoxyribonucleic acid. Transformation did not occur. Avery had found the inheritance molecule, DNA!Erwin Chargaff
To understand the DNA molecule better scientists were trying to make a model to understand how it works and what it does. In the 1940’s another scientist named Erwin Chargaff noticed a pattern in the amounts of the four bases: adenine, guanine, cytosine, and thymine. He took samples of DNA of different cells and found that the amount of adenine was almost equal to the amount of thymine, and that the amount of guanine was almost equal to the amount of cytosine. Thus you could say: A=T, and G=C. This discovery later became Chargaff’s Rule.Rosalind Franklin and Maurice Wilkins
Two scientists named, Rosalind Franklin and Maurice Wilkins, decided to try to make a crystal of the DNA molecule. If they could get DNA to crystallize, then they could make an x-ray pattern, thus resulting in understanding how DNA works. These two scientists were successful and obtained an x-ray pattern. The pattern appeared to contain rungs, like those on a ladder between to strands that are side by side. It also showed by an “X” shape that DNA had a helix shape.James Watson and Francis Crick
In 1953 two scientists, James Watson and Francis Crick, were trying to put together a model of DNA. When they saw Franklin and Wilkin's picture of the X-ray they had enough information to make an accurate model. They created a model that has not been changed much since then. Their model showed a double helix with little rungs connecting the two strands. These rungs were the bases of a nucleotide. At first Watson and Crick were set back with a problem, how to bond the bases together, and how to solve the problem of the sizes of the bases. Adenine and Guanine were purines having two carbon-nitrogen rings in their structures. Thymine and Cytosine were pyrimidines having one carbon-nitrogen ring in its structure. If DNA were to have its bases pair up so that the purines and the pyrimidines were together, then it would look wobly and crooked. Watson and Crick then found that if they paired Thymine with Adenine and Guanine with Cytosine DNA would look uniform. This pairing was also in accordance with Cargaff's rule. They also found that a hydrogen bond could be formed between the two pairs of bases. In all DNA strands if one side has a Thymine base then the other has the opposite: Adenine and so on with Guanine and Cytosine. Each side is a complete compliment of the other.A Person to Praise
By using the picture of the crystallized DNA, Watson and Crick were able to put together the model of DNA. Some have speculated that they did not give Rosalind Franklin enough credit for her work; she had certainly made history. Watson and Crick did use the new information very quickly as it is shown by the fact that their paper showing the model of DNA was published in the same issue of Nature as Franklin's picture. Watson and Crick, did, though, use this new information and information from Avery, Chargaff, Griffith, and others. They simply pieced together the puzzle. The Nobel Prize was awarded a few years after the presentation of the model to Watson, Crick, and Maurice Wilkins. Rosalind Franklin did not receive the prize because she had died of cancer by this time. Maurice Wilkins was able to share the prize with Watson and Crick, though, because of his work with Franklin. Her accomplishment should never be forgotten.
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