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History of DNA Timeline

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Mauli Chothani

on 27 March 2011

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Transcript of History of DNA Timeline

History of DNA Timeline Friedrich Miescher- 1868-1869 Swiss biologist, Miescher starts off the research of DNA by using disposable surgery bandages in a local hospital to isolate nucleic acid from pus cells. He found a substance called nuclein (which is now called nucleic acids) which has nitrogen and phosphorus within but no sulfur meaning that nuclein was not a protein. Nuclein also contains DNA (acidic portion) along with histones (packaged protein). Miescher also found a similar substance of nuclein in the heads of salmon sperm cells. The major contribution which led to the understanding of DNA is he was the first person to purify DNA from extracted nuclei. His research also helped other future scientists and researchers to identify DNA as genetic material. Miescher laid the foundation for other scientists to find more information about DNA. By: Mauli Chothani Frederick Griffith- 1928 Griffith is next in line and uses his kills to find that DNA is a molecule of inheritance. He conducted a well thought out experiment which contained two types of pneumonia: virulent and non-virulent, and mice. When he added the virulent pneumonia into a mouse, it died. However, when he put the non-virulent pneumonia into a mouse, it survived. Gathering his information, he heated the virulent pneumonia to kill the disease and then injected it into another mouse which did live. Taking this step a bit further, Griffith heated virulent pneumonia and non-virulent pneumonia to kill the disease, and injected it to a mouse which didn’t end up living. Griffith carried out all these experiments because he thought that the virulent bacteria which was killed, passed a characteristic which he thought was the inheritance molecule, to the non-virulent bacteria to make it virulent. He called this whole act of passing the inheritance molecule, transformation. Griffith’s contribution to the understanding of DNA is transformation was the first step in linking DNA to heredity in cells. Also, by conducting his experiment, it led to evidence that DNA is genetic material. Scientists used Griffith’s ideas to build off their experiments. Watson and Crick- 1953 Watson and Crick worked together to make a model of DNA by using information from previous scientists. The model they created consisted of a double helix with rings (bases of a nucleotide) which connected the two strands. The two strands of DNA are complementary and go in opposite directions. With complementary pairing, it guarantees that there’s an exact duplicate copy being made. Adenine and Guanine are purines meaning that in their structure, they have two carbon-nitrogen rings whereas Thymine and Cytosine are pyrimidines meaning that in their structure, they have one carbon-nitrogen ring. The base pairs Adenine and Thymine always pair up and the base pars Guanine and Cytosine always pair up which is tied to Chargaff’s rule. Furthermore, hydrogen bonds connect the two pairs of bases. The contribution Watson and Crick made is very significant. By the vast knowledge they had, it helped us figure out many new advances such as cloning a human DNA strand. It also answered some human genetic questions and their experiments inspired other scientists which led to other, newer ideas. Erwin Chargaff- 1950 Chargaff tried to figure out more information about DNA by performing many tests. He realized a pattern in the four nitrogenous bases: adenine, guanine, cytosine, and thymine. After taking samples of DNA of different cells, he found the amount of adenine was relatively close to the amount of thymine and the amount of guanine was relatively close to the amount of cytosine. The A=T and G=C was known as Chargaff’s rule. He also found that the amount of DNA in different species had a different ratio of the nitrogenous bases. Chargaff’s contribution of the experiment which led to the understanding of DNA is he found the structure which combines adenine and thymine and pairs up guanine and cytosine. He also realized that DNA played a very important part in a transformation which could be a major part of genes. He laid a foundation for Watson and Crick. Oswald Avery, Colin Macleod, Maclyn McCarty- 1944 Avery, Macleod, and McCarty all worked together at Rocketfeller Institute. They continued Griffith’s experiment and tried to find a more specific conclusion. They removed Streptococcus pneumonia (harmful S bacteria which killed the mice), proteins, and other substances, and then mixed harmless R bacteria with the different substances. Only the substances mixed with DNA transformed to the S bacteria. Unlike Griffith’s experiment, Avery, Macleod, and McCarty used a test tube, instead of the mice. The contribution Avery, Macleod, and McCarty made was their experiment entailed that DNA is a “transforming factor”, not proteins or other substances. The “transforming factor” is that all genes are made of DNA. Also, they found that DNA is the material in which genes and chromosomes are made, and DNA is the genetic material in organisms. Lastly, Avery and his laboratory team laid the platform for DNA research for other scientists. Alfred Hershy and Marsha Chase- 1952 Working together, Hershy and Chase accomplished many experiments of DNA. They classified DNA as genetic material of small viruses that infect bacteria called phages, and all the other organisms as well. Phages have a protein coat which keeps the genetic material inside. However, when they encounter bacterium and is infected, the genetic material transfer to the bacterium but the protein cover is still outside. With two experiments conducted using radioactive phosphorous DNA infected bacteria, and radioactive sulfur protein infected bacteria, they discovered that bacteria separated from the protein coat of phages, and blended using centrifugation in both experiments. The radioactivity was found in different places for both experiments though. In the first experiment, the radioactivity was found in the bacteria which were infected, whereas in the second experiment, the radioactivity was found in the phage protein coat. These experiments showed that DNA is the genetic material of phages, but the protein coat doesn’t transmit genetic information. The contribution Hershy and Chase made to the understanding of DNA is they studied viruses in depth and found that nonliving particles, smaller than cells, can infect living organisms. They also confirmed DNA’s role in hereditary. Lastly, they proved that DNA was the genetic material, not protein because people were still uncertain with Avery, MacLeod, and McCarty’s experiment. Franklin did research on DNA using X-ray crystallography, which can sometimes be called X-ray diffraction. She discovered that DNA can crystallize in two different forms called the A form and the B form and she found a method to separate those two forms. Using the X-ray crystallography, she also found that the sugar-phosphate backbone of DNA is on the outside, not on the inside as once was thought. She also noticed the helical structure has only two stands instead of three, and is called the double helix. She also could give many facts about the shape and size of the double helix using her creation. Franklin’s contribution to the understanding of DNA was she led to more understanding about the DNA helical structure. Perhaps, without her, the question of DNA shape might still have been unanswered. Rosalind Franklin- 1952-1953 Working with Franklin, Wilkins also used X-ray diffraction to create good quality, clear images of DNA to take a look at the structure. He informed Watson and Crick about the studies he gathered about the double helix structure of DNA so they could make a model. He inspired Watson and made him set a goal to achieve that he could unravel the complicated mystery to find the blueprint of life. The contribution Wilkins made to DNA is he had a great achievement to understand the genetic blueprint of life. He played a critical role and discovered the structure of DNA. Additionally, he was called the “third man of the double helix”, after Watson and Crick who took Wilkins’s ideas a step further. Furthermore, Wilkins was a very crucial aspect in the understanding of DNA because if it weren’t for him showing the X-rays to Watson and Crick, it would have taken longer to create the 3D model of DNA. Maurice Wilkins- 1953
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