Chapter 16 DNA & Replication

Slide 2 of 24 Bell Ringer 1. On a sheet of paper 2. Write down everything you know about DNA -- Who discovered DNA? -- What is the structure of DNA? -- How does DNA differ from RNA?

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Slide 4 of 24 The Beginnings  T. H. Morgan’s group showed that genes are located on chromosomes  The two components of chromosomes—DNA and protein— were candidates for the genetic material  The role of DNA in heredity was first discovered by studying bacteria and the viruses that infect them  The discovery of the genetic role of DNA began with research by Frederick Griffith in 1928

Slide 5 of 24 Griffin & Transformation  Griffin looked at bacteria & mice  Major finding = Transformation  Killed disease-causing bacteria + live, harmless bacteria  Result: Live, disease-causing bacteria  Transformation – change in genotype and phenotype due to uptake of foreign DNA

Slide 6 of 24 Living S cells (control) Living R cells (control) Heat-killed S cells (control) Mixture of heat-killed S cells and living R cells Mouse dies Living S cells Healthy Mouse Mouse dies

Slide 7 of 24 Hershey & Chase  What is responsible for transformation?  Dumb question now, but not so at the time  Bacteriophages – viruses than infect bacteria  Consist of protein + DNA  Which is the transformative agent?

Slide 8 of 24 EXPERIMENT Phage DNA Bacterial cell Radioactive protein Radioactive DNA Batch 1: radioactive sulfur ( 35 S) Batch 2: radioactive phosphorus ( 32 P)

Slide 9 of 24 EXPERIMENT Phage DNA Bacterial cell Radioactive protein Radioactive DNA Batch 1: radioactive sulfur ( 35 S) Batch 2: radioactive phosphorus ( 32 P) Empty protein shell Phage DNA

Slide 10 of 24 EXPERIMENT Phage DNA Bacterial cell Radioactive protein Radioactive DNA Batch 1: radioactive sulfur ( 35 S) Batch 2: radioactive phosphorus ( 32 P) Empty protein shell Phage DNA Centrifuge Pellet Pellet (bacterial cells and contents) Radioactivity (phage protein) in liquid Radioactivity (phage DNA) in pellet

Slide 11 of 24 Chargaff’s Rules In DNA: [A] = [T] & [G] = [C]  Why would this be true?

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Slide 13 of 24 Structural Model of DNA?  M. Wilkins & R. Franklin use X-ray crystallography to study molecular structure  Watson & Crick “deduced” that DNA was 2-stranded  Double Helix

Slide 14 of 24 DNA Replication  DNA  DNA  2 strands separate, and each one is paired using complementary bases

Slide 15 of 24 Themes (meh.)  Science as a process  Regulation  Interdependence in nature  Science, Technology, & Society

Slide 16 of 24 Semiconservative Replication  Each daughter molecule = 1 old strand (Conserved from parent strand) + 1 newly replicated strand  Called Semiconservative  Half of the strands are conserved from the parent  Competing (Incorrect models): Conservative & Dispersive

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Slide 18 of 24 DNA Replication  16_05DNAandRNAStructure  16_07DNADoubleHelix  16_09Overview

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Slide 21 of 24 Telomeres  Eukaryotic chromosomal DNA molecules have at their ends nucleotide sequences called telomeres  Telomeres do not prevent the shortening of DNA molecules, but they do postpone the erosion of genes near the ends of DNA molecules  It has been proposed that the shortening of telomeres is connected to aging  Telomerase – enzyme that lengthens the telomere  Telomerase in cancerous cells?

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Slide 24 of 24 PROKARYOTE EUKARYOTE