DNA & Replication

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?

4. 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

5. 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

6. 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

7. 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?

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

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

10. 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

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

13. 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

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

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

16. 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

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

21. 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?

24. PROKARYOTE EUKARYOTE