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The Discovery of DNA the Contribution of Frederick Griffith

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The Discovery of DNA the Contribution of Frederick Griffith http://www.juliantrubin.com/bigten/dnaexperiments.html About DNA The Discovery of DNA As early as 1848, Wilhelm Hofmeister, a German botanist, has observed that cell nuclei resolve themselves into small, rodlike bodies during mitosis. Later these structures were found to absorb certain dyes and so came to be called chromosomes (colored bodies). In 1869, Friedrich Miescher, a Swiss physician, isolated a substance from cell nuclei, that he called nuclein - now known as DNA. During the early years of the 20th century, cellular studies using ordinary light microscopes clarified the behavior of chromosomes during mitosis and meiosis, Animation of the structure of a section which led to the conclusion that chromosomes are the of DNA. The bases lie horizontally carriers of genes – the basic units of heredity. between the two spiraling strands. The chromosomes of eukaryotes contain a variety of proteins in addition to DNA. Soon the question arose whether the nucleic acids (DNA) or proteins, or both together, are the carriers of the genetic information. Until the early 1950s most biologists were inclined to believe that the proteins were the chief carriers if heredity. Nucleic acids contain only four different unitary building blocks, but proteins are made up of 20 different amino acids. Proteins therefore appeared to have a greater diversity structure, and the diversity of the genes seemed first likely to rest on the diversity of the proteins. The Contribution of Frederick Griffith In 1928, Frederick Griffith, an English army doctor, wanted to make a vaccine against a bacteria named Streptococcus pneumoniae, which caused a type of pneumonia. Since the time of Pasteur, about 50 years before, vaccines had been made using killed microorganisms which could be injected into patients to elicit the immune response of live cells without risk of disease. Though he failed in making the vaccine he stumbled on a demonstration of the transmission of genetic instructions by a process we now call the "transformation principle". He found that the bacterium had two forms when grown on agar plates, a smooth (S) and a rough (R) form. The R bacteria were harmless, but the S bacteria were lethal when injected into mice. Heat-killed S cells were also harmless - the same effect seen by Pasteur. However, surprisingly when live R cells were mixed with killed S cells and injected into mice the mice died, and the bacteria rescued from the mice had been "transformed" into the S type. This experiment strongly implied that genetic material had been transferred from the dead to the live cell. It was hard to be certain of this, or to know what exactly genetic material was transferred and was responsible for the transformation process. Griffith's Experiment from 1928 DNA is the Transforming Factor Sixteen years later, in 1944, the team of Avery, MacLeod and McCarty revisited this experiment and attempted a more definitive experiment. They extracted from Streptococcus pneumoniae S bacteria nucleoid purified DNA, proteins and other materials and mixed R bacteria with these different materials, and only those mixed with DNA were transformed into S bacteria. For their experiments they used a test tube assay instead of mice. This Experiment strongly implied that DNA is the “transforming factor” and not proteins or other materials and by this was demonstrated what is known to us as the transforming principle - that genes are made of DNA. Amazingly, not everyone was convinced by the experiments of Avery's, MacLeod's and McCarty's. It was the experiments of Hershey and Chase (1952) that finally proved that DNA was the genetic material and not protein. While Avery and his team were nominated several times for the Nobel Prize, they never received it. It is a universally recognized omission of the Nobel committee since their work was a blazing discovery that changed everything. For more about this topic see in the link section "The Nobel Prize Omission" Repeat Avery, MacLeod and McCarty's Experiments Warning: Before you start, please pay notice that these experiments can be dangerous since you will have to experiment with bacteria that can be infectious and other chemicals, materials and apparatus that can be dangerous for your health. As a rule: this experiment should be performed under the supervision of professionals familiar with chemical, biomedical and laboratory safety procedures. Among others, it is not so simple to obtain some chemical or bio materials and supplies and use them properly and safely in these experiments. If you are a high school student do not try anything by yourself before you consult your teachers, parents or other knowledgeable adults and experts. Do not try to do this experiment, or any other activity related to it, alone! Notify your parents and school authorities before you begin - wait for their approval. A few laboratory biological safety links: http://www.who.int/csr/resources/publications/biosafety/Biosafety7.pdf http://researchcompliance.uc.edu/biosafety/Biosafety-Manual.pdf After we have clarified the safety issue, a few useful remarks before you begin: These experiments are not as simple as they look, and nevertheless they were performed many years ago they still need some biochemistry and bacteriology extra skills, at least college level. You'll need some professional help. These experiments are somewhat costly and you’ll need some expensive materials and scientific instruments. A school science lab will not suffice for this end, not only for lack of scientific means but also for safety consideration. You’ll have to ask permission to use a university lab or other proper scientific institution – not a simple accomplishment. These experiments are intended mainly for college students or very high motivated and advanced high school students and teachers (for an award winning science fair project). If you have decided to embark on this challenge, first of all, address the safety concerns mentioned above. Now, ensure that you understand the basic principals of the Avery and coworkers experiment. The following animation is a good place to start and to figure out in a concise manner what is all this about: http://www.dnaftb.org/dnaftb/17/animation/animation.html The detailed account of Avery, MacLeod and McCarty's Experiments could be found in their paper "Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III", published in the February 1944 issue of the Journal of Experimental Medicine, in which Avery and his colleagues suggest that DNA, rather than protein as widely believed at the time, may be the hereditary material of bacteria and could be analogous to genes in higher organisms. A few links pointing to this article: http://www.twiv.tv/dna.pdf http://202.114.65.51/fzjx/wsw/newindex/wswfzjs/pdf/24avery.pdf http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2229990/ Surf the web further and consult scientific libraries, databases and relevant experts, and if you are a high school student, consult also your teachers and other knowledgeable adults and professionals. Take in account that it's also possible to repeat other related experiments as well. For example: the mentioned above Hershey and Chase (1952). Good Luck http://www.scienceinschool.org/2006/issue1/discoveringdna Discovering DNA Dean Madden Dean Madden from the National Centre for Biotechnology Education at the University of Reading, UK, describes how DNA was discovered - and how it can be simply extracted in the classroom. Johann Friedrich Miescher In 1868, Johann Friedrich Miescher travelled from his native Switzerland to Tübingen in Germany. The 24-year-old had come to study in the laboratory of Ernst Felix Hoppe-Seyler, a pioneering biochemist who coined the modern name for the red pigment in blood: haemoglobin. After several months of toil in a laboratory in the cellar of Tübingen Castle, Miescher managed to isolate a previously unknown acidic substance from white blood cells (leucocytes) which had been washed from pus-laden bandages from a nearby hospital. Miescher called his discovery 'nuclein' because it was found in the nuclei of the cells. This substance was impure, however, and Hoppe-Seyler insisted on repeating the work himself before he would allow an account to be published in his newly formed biochemistry journal. Upon returning to his home in Basel in 1870, Miescher refined the method and was able to extract nuclear material from the sperm of the salmon for which, in those days, the Rhine was famed. Like those in leucocytes, the nuclei in sperm cells are relatively large. From these, Miescher extracted pure nuclein for the first time. In 1889 a pupil of his, Richard Altmann, gave us the modern term for nuclein: nucleic acid. Thus, in 2003, we celebrated the golden jubilee of the double helix and not '50 years of DNA'. The laboratory in Tübingen where Miescher isolated nuclein. Photo courtesy of the University of Tübingen Library, Tübingen, Germany To a science teacher, an account of Miescher's methods makes fascinating reading, not least because of the crude techniques available and the striking resemblance they bear to many of today's classroom protocols. Compared with Miescher, however, today's teachers have an easy time. With no refrigeration, Miescher had to start work at 5 a.m. to ensure that the reagents were cold enough to precipitate DNA, and he had to prepare his own protease enzymes from the stomachs of freshly slaughtered pigs (Judson, 1996). Classroom protocols The isolation of DNA from everyday materials has become a popular and widespread activity in school laboratories over the past 20 years. Although similar practical protocols had been described previously (e.g. Sands, 1970), these were not widely adopted owing to their complexity and the hazardous nature of several of the required reagents (Falconer & Hayes, 1986).
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