1 DNA

2 DNA  Deoxyribonucleic acid  found in the nucleus of every cell  DNA and proteins make up chromosomes – contain traits  sections of it make up genes

3 DNA

4 History of DNA

5 Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA

6 Transformation Fred Griffith worked with harmful Smooth (S) and harmless Rough (R) strain Pneumoccocus bacteria - pneumonia He found that R strain could become harmful when it took in DNA from heat-killed S strain Study suggested that DNA was probably the genetic material

7 Griffith’s Experiment

8 History of DNA Oswald Avery  1944  performed Griffith’s experiment but added enzymes to kill proteins, lipids, carbs, and RNA and transformation still occurred

9 History of DNA Oswald Avery  1944  added enzymes to kill DNA and transformation didn’t occur

10 History of DNA Oswald Avery  1944  proved DNA makes up genes and chromosomes

11 History of DNA Alfred Hershey and Martha Chase  1952  Conducted a series of experiments with bacteriophages – virus that infects bacteria- which identified DNA, not protein, to be the genetic material of cells.

The Hershey-Chase Experiment Figure 10.1B Mix radioactively labeled phages with bacteria. The phages infect the bacterial cells. Phage Bacterium Radioactive protein DNA Empty protein shell 12 Agitate in a blender to separate phages outside the bacteria from the cells and their contents. 3 Centrifuge the mixture so bacteria form a pellet at the bottom of the test tube. 4 Measure the radioactivity in the pellet and liquid. Batch 1 Radioactive protein Batch 2 Radioactive DNA Radioactive DNA Phage DNA Centrifuge Pellet Radioactivity in liquid Radioactivity in pellet Pellet Centrifuge

13 Erwin Chargaff Discovered two important rules to the structure of DNADiscovered two important rules to the structure of DNA Showed that the number of G = C and A = TShowed that the number of G = C and A = T Showed that DNA composition varies between speciesShowed that DNA composition varies between species Known as Chargaff’s RulesKnown as Chargaff’s Rules

14 DNA Structure Rosalind Franklin  1951 took x-ray diffraction photographs of DNA X-ray diffraction reveals the shape of a molecule

15 Rosalind Franklin

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17 History of DNA James Watson and Francis Crick   1953  Used Franklin’s x- rays to discover the structure of DNA  called structure the double helix  Won Nobel Prize in 1962

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20 History of DNA Alfred Hershey and Martha Chase  1952  In the first experiment, phages with radioactive 32 P-labeled DNA infected bacteria. In a second experiment, phages with radioactive 35 S-labeled protein infected bacteria. In the first experiment, most radioactivity was found in the infected bacteria, while in the second experiment most radioactivity was found in the phage coat. These experiments demonstrated that DNA is the genetic material of phage and that protein does not transmit genetic information.