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Chapter 14-15 Lecture Outline

Chapter 14-15 Lecture Outline - Biology 100 Vandan Desai...

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Biology 100 Vandan Desai Chapter 14: Dglyph1197A Synthesis / Chapter 15: How Genes Work (Lecture Outline— Only Sections Covered In Class ) ---------------------------------------------------------------------------------------------------------------------------- I. Dglyph1197A as the Hereditary Material A. Fredrick Griffith’s experiment on Streptococcus pneumonia bacteria introduced the concept of transformation —assimilation of DNA from another organism i. Some strains of S. pneumoniae infect mice , causing pneumonia 1. Virulent strains form smooth (S) colonies 2. Benign strains form rough (R) colonies and do not cause disease ii. Griffith prepared four treatments to elucidate the interactions of S and R strains by injecting mice with: 1. Living benign R cells— no disease developed in injected mice 2. Living virulent S cells—injected mice died 3. Heat-killed S cells— no disease developed in injected mice 4. Heat-killed S cells mixed with living R cells—injected mice died iii. Conclusion: something from the dead S cells, a “ transforming factor ,” transformed the living R cells from benign to virulent B. Is DNA the Genetic Material? i. Known since the late 1800s that chromosomes composed of Dglyph817A and proteins ii. Chromosome theory confirmed around 1920 so transforming factor had to be either of the two—DNA or protein iii. Thought genes made up of proteins 1. Many complex and highly regulated chemical reactions occur in cells 2. Proteins have limitless variation in structure and function 3. DNA, on the other hand, is simple and composed of only four deoxyribonucleotides; repetitive and uninteresting C. Identification of the “Transforming Factor”— Avery , MacLeod , and McCarty i. The researchers, after removing lipids and carbohydrates, extracted proteins and nucleic acids from heat-killed S cells ii. They divided the extract into three solutions, each treated in a different way: 1. They treated one solution with proteases to destroy proteins 2. They treated one solution with Rglyph817ases to destroy Rglyph817A 3. They treated one solution with Dglyph817ases to destroy Dglyph817A iii. The researchers added the treated extracts to R cells : 1. Extracts treated with DNases did not transform R cells to S cells, but those treated with proteases and RNases did 2. Conclusion: Dglyph817A must be the transforming factor , thus the genetic material D. Hershey and Chase’s T2 virus experiments finally convinced skeptics that DNA was the genetic material i. T2 attaches to host cell ( Escherichia coli ), leaves a capsule outside, and injects a material inside ii. Host cell begins producing copies of T2 virus 1. The injected material from the virus must be hereditary material because it triggers the production of new T2 viruses 2. Capsule does not enter the cell (remains outside as a “ ghost
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