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Ch.11 - Alison Lindsay Ch.11 Griffith's"Transforming Factor...

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Alison Lindsay Ch.11 Griffith's "Transforming Factor" Is the Genetic Material 1928 two strains of a bacterial species: one caused pneumonia fatal to mice, the other was harmless Heat kills the deadly strain of the bacterium, making it harmless Figure 11-1 Griffith showed that although a deadly strain of bacteria could be made harmless by heating it, some factor in that strain is still able to change other harmless bacteria into deadly ones. He called this the "transforming factor." all of the descendants of the transformed bacteria inherited the killer trait Avery Shows DNA Is the Transforming Factor protein and DNA were the contestants of inheritance carriers 1944 took Griffith's experiments one step further treated Griffith's mixture of heat-treated deadly strain and live harmless strain with protein-destroying enzymes treated the other mixture with DNA-destroying enzymes the colonies failed to transform Avery concluded that DNA is the genetic material of the cell Virus Experiments Provide More Evidence Many people thought DNA seemed too simple to account for the large variety of traits inherited by organisms 1952, biologists Alfred Hershey and Martha Chase
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virus - a package of nucleic acid wrapped in a protein coat; not made of cells, and can only reproduce by infecting a living cell with its genetic material A virus that infects bacteria is called a bacteriophage , or phage for short Phage-DNA on the inside, coated with protein on the outside radioactive isotope of sulfur to label only the phages' protein coats In the other batch of phages, they used a radioactive isotope of phosphorus to label only DNA phages infect separate cultures of nonradioactive bacterial cells whirled each culture in a blender to shake loose any parts of the phages that remained outside the bacterial cells measured radioactivity in the loose phage parts and in the bacterial cells phage protein coats were labeled- radioactivity outside the cells phage DNA was labeled- radioactivity inside the cells the phage's DNA entered the bacterial cell during infection, but the proteins did not DNA must carry the genetic information responsible for producing new phages The Building Blocks of DNA The heritable genetic information of an organism is stored in the molecule called deoxyribonucleic acid (DNA)
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