Chapter 16 (2)

Chapter 16 (2) - Chapter 16 The Molecular Basis of...

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Unformatted text preview: Chapter 16 The Molecular Basis of Inheritance Overview: Lifes Operating Instructions In 1953, James Watson and Francis Crick shook the world With an elegant double-helical model for the structure of deoxyribonucleic acid, or DNA Figure 16.1 DNA Most celebrated molecule of our time Hereditary information Encoded in chemical language of DNA & reproduced in all cells of your body DNA program Directs development of many different types of traits Concept 16.1: DNA is the genetic material Early in 20th century Identification of molecules of inheritance loomed as major challenge to biologists The Search for the Genetic Material: Scientific Inquiry Role of DNA in heredity Studying bacteria & viruses that infect them Evidence That DNA Can Transform Bacteria Griffith was studying Streptococcus pneumoniae Bacterium that causes pneumonia in mammals Worked with 2 strains of bacterium Pathogenic & nonpathogenic When he mixed heat-killed remains of pathogenic strain With living cells of nonpathogenic strain, some living cells became pathogenic Bacteria of the S (smooth) strain of Streptococcus pneumoniae are pathogenic because they have a capsule that protects them from an animals defense system. Bacteria of the R (rough) strain lack a capsule and are nonpathogenic. Frederick Griffith injected mice with the two strains as shown below: Griffith concluded that the living R bacteria had been transformed into pathogenic S bacteria by an unknown, heritable substance from the dead S cells. EXPERIMENT RESULTS CONCLUSION Living S (control) cells Living R (control) cells Heat-killed (control) S cells Mixture of heat-killed S cells and living R cells Mouse dies Mouse healthy Mouse healthy Mouse dies Living S cells are found in blood sample. Figure 16.2 Griffith called it transformation Change in genotype & phenotype due to assimilation of external DNA Evidence That Viral DNA Can Program Cells Viruses that infect bacteria, bacteriophages Widely used as tools by researchers in molecular genetics Figure 16.3 Phage head Tail Tail fiber DNA Bacterial cell 100 nm Hershey & Chase Performed expts. showing DNA is genetic mtl. of phage known as T2 The Hershey and Chase experiment In their famous 1952 experiment, Alfred Hershey and Martha Chase used radioactive sulfur and phosphorus to trace the fates of the protein and DNA, respectively, of T2 phages that infected bacterial cells. Radioactivity (phage protein) in liquid Phage Bacterial cell Radioactive protein Empty protein shell Phage DNA DNA Centrifuge Pellet (bacterial cells and contents) Radioactive DNA Centrifuge Pellet Batch 1: Phages were grown with radioactive sulfur ( 35 S ), which was incorporated into phage protein (pink)....
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This note was uploaded on 01/18/2011 for the course BIO 103 taught by Professor Sanders during the Spring '10 term at Northwestern IA.

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Chapter 16 (2) - Chapter 16 The Molecular Basis of...

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