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Understanding DNA: Structure, Replication, and Its Role in Genetics

This resource delves into the fundamentals of DNA, covering its discovery, structure, and differences from RNA. It explores pivotal contributions from scientists like T.H. Morgan, Frederick Griffith, and the Hershey-Chase experiment, which demonstrated DNA's role as the genetic material. Key concepts such as transformation, Chargaff's rules, and the double helix model by Watson and Crick are highlighted. Additionally, it discusses DNA replication, including the semiconservative model, telomeres, and their implications for aging and cancer.

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Understanding DNA: Structure, Replication, and Its Role in Genetics

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Presentation Transcript

  1. DNA & Replication

  2. 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?

  3. 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

  4. 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

  5. Mixture of heat-killed S cells and living R cells Heat-killed S cells (control) Living S cells (control) Living R cells (control) Living S cells Healthy Mouse Healthy Mouse Mouse dies Mouse dies

  6. 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?

  7. EXPERIMENT Radioactive protein Phage Bacterial cell DNA Batch 1: radioactive sulfur (35S) Radioactive DNA Batch 2: radioactive phosphorus (32P)

  8. EXPERIMENT Empty protein shell Radioactive protein Phage Bacterial cell DNA Batch 1: radioactive sulfur (35S) Phage DNA Radioactive DNA Batch 2: radioactive phosphorus (32P)

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

  10. Chargaff’s Rules In DNA: [A] = [T] & [G] = [C] • Why would this be true?

  11. 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

  12. DNA Replication • DNA  DNA • 2 strands separate, and each one is paired using complementary bases

  13. Themes (meh.) • Science as a process • Regulation • Interdependence in nature • Science, Technology, & Society

  14. 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

  15. DNA Replication • 16_05DNAandRNAStructure • 16_07DNADoubleHelix • 16_09Overview

  16. 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?

  17. PROKARYOTE EUKARYOTE

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