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Scientists of DNA
Transcript of Scientists of DNA
Discovery of DNA: Timeline
Matthew Meselson & Franklin Stahl: 1957
Procedure: They marked E. Coli with an isotope and centrifuged it. They did this in order to observe the replication of DNA through generations.
Oswald Theodore Avery: 1944
Procedure: Similar to and partially inspired by Griffith's experiment Avery's was very similar. He used the pneumoccous bacteria in strain S and R. The S strain being encapsulated and the R strain not. Griffith injected mice with S strain, R strain, Heat-killed S strain, A mixture of heat-killed S strain and live R strain. In this mix, he was able to isolate S strain bacteria from their blood although they were injected with killed of S strain bacteria. To confirm his findings, he used detergent to lyse his cells with different substances and combine them with R strain cells.
Erwin Chargaff: 1950
Rosalind Franklin: 1952
Procedure: Rosaline Franklin used x-ray crystallography on 2 DNA fragments. She tool "pictures" of the DNA and its shape, now refurred to as the infamous photo 51.
Martha Chace & Alfred Hershey: 1952
Procedure: Hershey and Chase used radioactive sulfer to mark DNA because DNA contains no sulfur. They used radioactive phosphorous to mark protein because protein contains no phospherous.They put these elements in bacteria cultures and watched as they replicated. They then but the culture in a blender.
James Watson & Francis Crick: 1953
Aurther Korenburg: 1958
Procedure: Korenburg exraced DNA Polymerase from E. Coli and used the bacteriophage phX174 as a guideline for synthesis. The phage reproduced in the E. Coli making a template for a the new DNA replication. Then, the strand was aligned with its corresponding bases, phosphates and sugars in order to complete its second half.
Marshall Nirenburg: 1961
Procedure: He synthesized RNA made only from certain codon combinations like UUU (uracil) and then he placed it in a mix of broken down bacteria. He did this for all the codon combinations.
Frederick Griffith: 1928
Friedrich Miescher: 1869
Procedure: Miescher examined the white blood cells of humans. He found it hard to get them from lymph glands but found bulks of them at local clinic on bandages covered in pus from infection. He collected these bandages, wiped off the pus and began to isolate his findings. He put the cells through an alcohol wash to get rid of the cell membership and pepsin wash to get rid of the remaining material until all he is left with is the nucleus of the cell. He added baking soda because he noticed that it would make the nucleus translucent then, he neutralized it with an acid and was left with solid DNA. He went on to repeat this with many different types of cells. He also tried burning the DNA.
Results: The substance dissolved when in a base and solidified when in an acid. He determined that it was made out of oxygen, hydrogen, nitrogen and phosphorous and that there was a unique ratio between the nitrogen and phosphorus. Also, His repetition of this on many different types of cells lead to the same outcome. It did not dissolve in pepsin solution and when he burned the DNA he deduced that it contained carbon, hydrogen, nitrogen, and oxygen.
Conclusion: He called the substance that he discovered nuclein. By the fact that the substance dissolved in a base and solidified in an acid he could conclude that the substance was more acid than it was basic. The fact that it did not dissolve in pepsin and that it contained phosphorous proved that it wasn't a protein because proteins contain sulfur and not phosphorus but the DNA did. The similar outcomes he received as he tested different types of cells solidifying the idea that almost every cell contained the substance that he found from the white blood cells.
Importance: This was the base of all discoveries made about DNA. Miescher discovered the presence of DNA and spurred many questions about DNA. He refuted the idea that the substance may be a protein and overall, his discovery is what enabled others to present further ideas abut DNA and genetics.
Procedure: Griffith observed two strains of Streptococcus pneumoniae, Type-III S and Type-II R. Type-III S had a protective polysaccharides capsule around it and thus to host can not fight it off by itself and Type-II R did not, so the host's immune system could fight off the bacteria. The bacteria varied in their look and ability to cause disease. He injected mice with either S or R strain of the bacteria and observed. He discovered that the S strains ability to cause disease was destroyed when heating it so, he injected some mice with heat-killed S bacteria and living R bacteria and, injected some mice with just heat-killed S bacteria. He also observed bacteria from the hearts of the mice injected with the mixture of the R and S strain.
Results: Mice injected with just the S strain died within a few days. Mice injected withe the R strain did not die. Mice injected with the mixture of the heated S strain and alive R strain died. Mice injected with only the heated S strain lived. The bacteria he got from the hears of the mice that were injected with the mixed strains had the smooth outer capsules associated with the S strain of the bacteria
Conclusion: He concluded that a chemical element in the diseased S cells and caused the R cells to develop S cell like qualities. Although he wasn't able to figure out exactly why this happened, he initiated the idea of the "transforming principle" or the early name for DNA (before they knew it was hereditary material). He had witnessed bacteria "transforming" from one type to another.
Importance: This discovery played an important part in the scientific community. Firstly, it enabled scientist to create more accurate and helpful forms of antibiotics against possible antibiotic "resistance" infections. Additionally, it helped propose the idea that DNA can "transfer" or cause one thing to change into another.
Results: Mice infected with only S train or mixture of Killed S strain and live R strain dies while, mice injected with only R strain or killed off S strain lived. When he lysed the S cells and combined them with R strain cells he ended up with S cells.
Conclusion: From this Avery, like Griffith, wondered what would cause the transformation. He noted that the culture of the bacteria in the mixed injection mice was S strained so the change in the live R strain was stable and inherited. He confirmed this when he lysed the S strain combined it with R strain and resulted in S strain. From his testing, he was able to conclude that the substance was not a protein or a carbohydrate in instead suspected it was a nucleic acid. Through their tests with lyseing the cells they could conclude that the "transforming principle" was in fact DNA.
Importance: This was important because Avery concluded that DNA was hereditary material and that it was made up of nucleotides. This laid groundwork for further exploration of DNA because of the generalizations made by him. He told scientists what DNA was made or and its purpose.
Procedure: Chargoff broke down DNA until he was just left withe the nitrogen fixing bases. He then used paper chromatography to separate all the bases from their pairs. In paper chromatography, paper is dipped in solution and the most soluble element of that solutions travels the furthest up the paper. He exposed the solution to UV light and was bale to tell how much of each base was in the DNA.
Results: The amount of adenine was equal to the amount of thymine and the amount of cytosine was equal to the amount of guanine.
Conclusion: The amount of one nitrogenous base is equal to the amount of its corresponding base. He also concluded that the ratios may differ from organism to organism
Importance: Chargaffs discovery confirmed the ideas of Watson and Crick. It al.lpowed scientists to know what DNA was made up of and enabled them to make further conclusions about DNA based on his rule.
Results: When they put the culture in the blender they noticed that the protein separated from the bacteria while the DNA had entered the cells and started replicating phage particles. The phage proteins remained attached to the bacterias cell walls on the outside. The Phage DNA was still inside the bacteria there although the bacteria didn't have any traces of phage protein.
Conclusion: From their experiments they could conclude that DNA was what carried genetic material and it is what is transferred through generation not proteins, as many during that time had thought.
Importance: By determining that DNA was the hereditary genetic material passed on they helped many other scientists with their DNA related discoveries. Technically, they paved the way for other DNA related theories and discoveries, like evolution, whose premise relies on the idea that DNA is hereditary material.
Results: Franklin found that the image she looked at of DNA looked like an X.
Conclusion: Her images lead to the idea that DNA would have a helix shape because of her knowledge that its was 3D and the X shaped image she had taken. She could also conclude that the phosphates were on the outside of the structure.
Importance: Her image paved the way for Watson and Crick to make their first model of the possible shape of DNA. Her idea was disputed by many but Watson and Crick brought light to it.
Procedure: Watson and Crick worked to build a model of DNA based on Rosalind Franklin's picture, They used her prediction and image to make a structural representation of what a DNA strand may have looked like. Overall, they combine the ideas of past scientists into one model of DNA
Results: Watson and Crick made an accurate model of DNA. Using Franklin's image, they could tell that the DNA was a helix shape like a twisted ladder.They had outer phosphates and sugar with nitrogen bases of adenine, thymine, cytosine and guanine. Based on Chargaff's rule to ratio of each pair of corresponding bases was equal.
Importance: This was important because now scientist know the answer to a primitive question, being what was the structure of DNA? This now enabled other scientists to make discoveries in DNA.
Results: They discovered two types of cell densities in the bacteria. One from reproduction and one from growth. They also discovered that they had bacterial genes from the parent and the successor.
Conclusion: They found out that DNA replicates in a semi-conservative manner. DNA is separated and a new strand is formed via bases of the parental strand creating a semi-new double-stranded piece of DNA.
Importance: Their discoveries, like all the others, aided the way for future DNA related discoveries like protein synthesis and much more.
Results: Active, Synthesized DNA
Conclusion: DNA can be synthesized
Impact: The discovery that it is possible to synthesize DNA, allowed for a larger amount of DNA to be studied in labs and for advances in the medical field
Results: Each set of 3 bases or codons would result in a certain amino acid. For example, UUU resulted in phenylalanine. Some combinations of bases in codons would result in the same amino acid. He did this until all the possible combinations were fulfilled .
Conclusion: A set of three nitrogen bases form a codon which codes for a certain amino acid. In order for a certain protein to be formed the order of bases on the strand of tRNA bust be in a particular order.
Importance: Nirenburg decoded almost all of the genetic sequence of codons and their resulting amino acids. This allowed for other scientists to discover more about protein synthesis and its importance. It also paved the way for the ideas of transcription and translation.
Conclusion: The structure of DNA is a double helix with sugar and phosphate sides and nitrogenous base center pegs connecting the two sides like the rungs of a twisted ladder.
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By: Ashna Patel
April 4, 2016
Term 3 Project
"Concept 19 The DNA Molecule Is Shaped like a Twisted Ladder." Rosalind Franklin. N.p., n.d. Web. 01 Apr. 2016.
"Important Scientists in the History of DNA Timeline." Timetoast. N.p., n.d. Web. 01 Apr. 2016.
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"Concept 15 DNA and Proteins Are Key Molecules of the Cell Nucleus."Friedrich Miescher. N.p., n.d. Web. 01 Apr. 2016.
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"Concept 17 A Gene Is Made of DNA." Oswald Theodore Avery. N.p., n.d. Web. 01 Apr. 2016.
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"Concept 15 DNA and Proteins Are Key Molecules of the Cell Nucleus."Friedrich Miescher. N.p., n.d. Web. 01 Apr. 2016.