Post on 02-Jan-2016
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DNA DNA
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DNADNA
Deoxyribonucleic acid found in the nucleus of every cell
DNA and proteins make up chromosomes – contain traits
sections of it make up genes
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DNADNA
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History History of DNAof DNA
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History of DNA
•Early scientists thought protein was the cell’s hereditary material because it was more complex than DNA
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TransformationTransformation• 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
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Griffith’s Griffith’s ExperimentExperiment
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History of DNAHistory of DNA
Oswald Avery 1944performed Griffith’s experiment but added enzymes to kill proteins, lipids, carbs, and RNA and transformation still occurred
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History of DNAHistory of DNA
Oswald Avery 1944 added enzymes to kill DNA and transformation didn’t occur
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History of DNAHistory of DNA
Oswald Avery 1944 proved DNA makes up genes and chromosomes
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History of DNAHistory of DNA
Alfred Hershey and Martha Chase1952
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 radioactivelylabeled phages with bacteria. The phages infect the bacterial cells.
Phage
Bacterium
Radioactiveprotein
DNA
Emptyprotein shell
1 2 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 1Radioactiveprotein
Batch 2RadioactiveDNA
RadioactiveDNA
PhageDNA
Centrifuge
Pellet
Radioactivityin liquid
Radioactivityin pelletPellet
Centrifuge
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Erwin ChargaffErwin Chargaff• Discovered two Discovered two
important rules to the important rules to the structure of DNAstructure of DNA
• Showed that the number Showed that the number of G = C and A = Tof G = C and A = T
• Showed that DNA Showed that DNA composition varies composition varies between speciesbetween species
• Known as Chargaff’s Known as Chargaff’s RulesRules
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DNA StructureDNA Structure•Rosalind Franklin
1951 • took x-ray diffraction
photographs of DNA •X-ray diffraction
reveals the shape of a molecule
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Rosalind FranklinRosalind Franklin
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History of DNAHistory of DNA James Watson and Francis Crick
1953Used Franklin’s x-
rays to discover the structure of DNA
called structure the double helix
Won Nobel Prize in 1962
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History of DNAHistory of DNA
Alfred Hershey and Martha Chase 1952
In the first experiment, phages with radioactive 32P-labeled DNA infected bacteria. In a second experiment, phages with radioactive 35S-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.