Discovery of DNA

Discovery of DNA - Discovery of DNA 1920s Since there are...

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Discovery of DNA 1920’s : Since there are only four nucleic acids in DNA (A, C, G, T) as opposed to twenty in protein; everyone assumed the latter was responsible for hereditary genetic information. Human genome has 20-30,000 genes. How? Of the 4 nucleic acids, 3 are read at a time; the combination of 3 nucleic acids allows for 4x4x4 = 64 building blocks. Also, varied length of combinations allow for more possibilities. 1928 : Frederick Griffith studied the bacteria responsible for pneumonia ( Streptococcus p.). He attempted to create a vaccine and though he failed, he discovered that there were two strains of the bacteria. S Strain : smooth appearance due to polysaccharide capsule; virulent R Strain : rough appearance; recognized by the host’s immune system Experiment 1: heated up S strain (killing the bacteria); injected into mouse; mouse lives. Experiment 2: mixed heated S strain with R strain and injected into mouse; mouse died. Something in the S strain caused the R strain to become the S strain; the change was stable and permanent -> R strain was “transformed”. 1944 : What is the substance from the S strain that caused virulence and was heritable? Avery’s lab was able to isolate different substances (RNA, protein, DNA, lipid, carbohydrate) and injected it into S-Strain cells. DNA was the only substance that was able to transform R to S
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This note was uploaded on 09/03/2010 for the course LS 252006132 taught by Professor Pham during the Summer '10 term at UCLA.

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Discovery of DNA - Discovery of DNA 1920s Since there are...

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