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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.