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Living S cells (control)

Mixture of heat-killed S cells and living R cells. EXPERIMENT. Living R cells (control). Living S cells (control). Heat-killed S cells (control). RESULTS. Mouse dies. Mouse healthy. Mouse healthy. Mouse dies. Living S cells. Phage head. Tail sheath. Tail fiber. DNA.

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Living S cells (control)

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  1. Mixture of heat-killed S cells and living R cells EXPERIMENT Living R cells (control) Living S cells (control) Heat-killed S cells (control) RESULTS Mouse dies Mouse healthy Mouse healthy Mouse dies Living S cells

  2. Phage head Tail sheath Tail fiber DNA 100 nm Bacterial cell

  3. 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

  4. Nitrogenous bases Sugar–phosphate backbone 5 end Thymine (T) Adenine (A) Cytosine (C) DNA nucleotide Phosphate Sugar (deoxyribose) 3 end Guanine (G)

  5. (b) Franklin’s X-ray diffraction photograph of DNA (a) Rosalind Franklin

  6. 5 end Hydrogen bond 3 end 1 nm 3.4 nm 3 end 0.34 nm 5 end (c) Space-filling model (a) Key features of DNA structure (b) Partial chemical structure

  7. Purine + purine: too wide Pyrimidine + pyrimidine: too narrow Purine + pyrimidine: width consistent with X-ray data

  8. Adenine (A) Thymine (T) Cytosine (C) Guanine (G)

  9. A T A T A T A T C G C G C G C G A T A T A A T T T A T A T T A A C C G C G C G G (c) “Daughter” DNA molecules, each consisting of one parental strand and one new strand (b) Separation of strands (a) Parent molecule

  10. First replication Second replication Parent cell (a) Conservative model (b) Semiconserva- tive model (c) Dispersive model

  11. EXPERIMENT Bacteria cultured in medium containing 15N Bacteria transferred to medium containing 14N 1 2 RESULTS DNA sample centrifuged after 20 min (after first application) 4 DNA sample centrifuged after 40 min (after second replication) Less dense 3 More dense CONCLUSION First replication Second replication Conservative model Semiconservative model Dispersive model

  12. Origin of replication Parental (template) strand Daughter (new) strand Replication fork Double- stranded DNA molecule Replication bubble 0.5 µm Two daughter DNA molecules (a) Origins of replication in E. coli Origin of replication Double-stranded DNA molecule Parental (template) strand Daughter (new) strand 0.25 µm Replication fork Bubble Two daughter DNA molecules (b) Origins of replication in eukaryotes

  13. Primase Single-strand binding proteins 3 Topoisomerase 5 3 RNA primer 5 5 3 Helicase

  14. New strand 5 end Template strand 3 end 5 end 3 end Sugar T A A T Base Phosphate C G C G G C G C DNA polymerase 3 end A A T T 3 end Pyrophosphate C C Nucleoside triphosphate 5 end 5 end

  15. Overview Origin of replication Leading strand Lagging strand Primer Lagging strand Leading strand Overall directions of replication Origin of replication 3 5 RNA primer 5 “Sliding clamp” 3 5 DNA poll III Parental DNA 3 5 5 3 5

  16. Overview Origin of replication Leading strand Lagging strand Lagging strand 2 1 Leading strand Overall directions of replication

  17. 3 5 3 5 Template strand 3 5 3 RNA primer 1 5 3 Okazaki fragment 5 3 1 5 3 5 3 2 5 1 5 3 3 5 1 2 5 3 3 5 1 2 Overall direction of replication

  18. Overview Origin of replication Lagging strand Leading strand Leading strand Lagging strand Single-strand binding protein Overall directions of replication Helicase Leading strand 5 DNA pol III 3 3 Primer Primase 5 3 Parental DNA Lagging strand DNA pol III 5 DNA pol I DNA ligase 4 3 5 3 2 1 3 5

  19. Nuclease DNA polymerase DNA ligase

  20. 5 Ends of parental DNA strands Leading strand Lagging strand 3 Last fragment Previous fragment RNA primer Lagging strand 5 3 Parental strand Removal of primers and replacement with DNA where a 3 end is available 5 3 Second round of replication 5 New leading strand 3 5 New lagging strand 3 Further rounds of replication Shorter and shorter daughter molecules

  21. Nucleosome (10 nm in diameter) DNA double helix (2 nm in diameter) H1 Histone tail Histones DNA, the double helix Histones Nucleosomes, or “beads on a string” (10-nm fiber)

  22. Chromatid (700 nm) 30-nm fiber Loops Scaffold 300-nm fiber Replicated chromosome (1,400 nm) 30-nm fiber Looped domains (300-nm fiber) Metaphase chromosome

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