Mixture of heat-killed S cells and living R cells Figure 16.2 EXPERIMENT Mixture of heat-killed S cells and living R cells Heat-killed S cells (control) Living S cells (control) Living R cells (control) RESULTS Figure 16.2 INQUIRY: Can a genetic trait be transferred between different bacterial strains? Griffith (1928) Mouse dies Mouse healthy Mouse healthy Mouse dies Living S cells

Phage head Tail sheath Tail fiber DNA 100 nm Bacterial cell Figure 16.3 Phage head Tail sheath Tail fiber Figure 16.3 Viruses infecting a bacterial cell. Hershey and Chase (1952) DNA 100 nm Bacterial cell

Radioactivity (phage protein) in liquid Phage Figure 16.4-3 EXPERIMENT Empty protein shell Radioactive protein Radioactivity (phage protein) in liquid Phage Bacterial cell Batch 1: Radioactive sulfur (35S) DNA Phage DNA Centrifuge Radioactive DNA Pellet (bacterial cells and contents) Figure 16.4 INQUIRY: Is protein or DNA the genetic material of phage T2? Batch 2: Radioactive phosphorus (32P) Centrifuge Radioactivity (phage DNA) in pellet Pellet

Sugar–phosphate backbone Figure 16.5 Sugar–phosphate backbone Nitrogenous bases 5 end Thymine (T) Adenine (A) Cytosine (C) Figure 16.5 The structure of a DNA strand. Phosphate Guanine (G) Sugar (deoxyribose) DNA nucleotide Nitrogenous base 3 end

Franklin’s X-ray diffraction photograph of DNA Figure 16.6 Figure 16.6 Rosalind Franklin and her X-ray diffraction photo of DNA. (a) Rosalind Franklin (b) Franklin’s X-ray diffraction photograph of DNA

Figure 16.1 Figure 16.1 How was the structure of DNA determined? Watson and Crick (Wilkins and Franklin) (1953)

5 end 3 end 3 end 5 end Hydrogen bond 3.4 nm 1 nm 0.34 nm (a) Figure 16.7 5 end C G Hydrogen bond C G 3 end G C G C T A 3.4 nm T A G C G C C G A T 1 nm C G T A C G G C C G A T Figure 16.7 The double helix. A T 3 end A T 0.34 nm 5 end T A (a) Key features of DNA structure (b) Partial chemical structure Space-filling model (c)

Purine  purine: too wide Figure 16.UN01 Purine  purine: too wide Pyrimidine  pyrimidine: too narrow Figure 16.UN01 In-text figure, p. 310 Purine  pyrimidine: width consistent with X-ray data

Sugar Sugar Adenine (A) Thymine (T) Sugar Sugar Guanine (G) Figure 16.8 Sugar Sugar Adenine (A) Thymine (T) Figure 16.8 Base pairing in DNA. Sugar Sugar Guanine (G) Cytosine (C)

(a) Parent molecule A T C G T A A T G C Figure 16.9-1 Figure 16.9 A model for DNA replication: the basic concept.

(a) Parent molecule (b) Separation of strands A T A T C G C G T A T A Figure 16.9-2 A T A T C G C G T A T A A T A T G C G C (a) Parent molecule (b) Separation of strands Figure 16.9 A model for DNA replication: the basic concept.

(a) Parent molecule (b) Separation of strands (c) Figure 16.9-3 A T A T A T A T C G C G C G C G T A T A T A T A A T A T A T A T G C G C G C G C (a) Parent molecule (b) Separation of strands (c) “Daughter” DNA molecules, each consisting of one parental strand and one new strand Figure 16.9 A model for DNA replication: the basic concept.

Parent cell First replication Second replication Figure 16.10 Parent cell First replication Second replication (a) Conservative model (b) Semiconservative model Figure 16.10 Three alternative models of DNA replication. (c) Dispersive model

Bacteria cultured in medium with 15N (heavy isotope) Figure 16.11a EXPERIMENT 1 2 Bacteria cultured in medium with 15N (heavy isotope) Bacteria transferred to medium with 14N (lighter isotope) RESULTS 3 Less dense DNA sample centrifuged after first replication 4 DNA sample centrifuged after second replication Figure 16.11 INQUIRY: Does DNA replication follow the conservative, semiconservative, or dispersive model? More dense

Semiconservative model Figure 16.11b CONCLUSION Predictions: First replication Second replication Conservative model Semiconservative model Figure 16.11 INQUIRY: Does DNA replication follow the conservative, semiconservative, or dispersive model? Dispersive model

(a) Origin of replication in an E. coli cell Figure 16.12a (a) Origin of replication in an E. coli cell Origin of replication Parental (template) strand Daughter (new) strand Double- stranded DNA molecule Replication fork Replication bubble Two daughter DNA molecules Figure 16.12 Origins of replication in E. coli and eukaryotes. 0.5 m

(b) Origins of replication in a eukaryotic cell Figure 16.12b (b) Origins of replication in a eukaryotic cell Double-stranded DNA molecule Origin of replication Parental (template) strand Daughter (new) strand Bubble Replication fork Figure 16.12 Origins of replication in E. coli and eukaryotes. Two daughter DNA molecules 0.25 m

Single-strand binding proteins Figure 16.13 Primase 3 Topoisomerase RNA primer 5 3 5 3 Helicase Figure 16.13 Some of the proteins involved in the initiation of DNA replication. 5 Single-strand binding proteins

Nucleoside triphosphate Figure 16.14 New strand Template strand 5 3 5 3 Sugar A T A T Base Phosphate C G C G G C G C DNA polymerase OH 3 A T A Figure 16.14 Incorporation of a nucleotide into a DNA strand. T P OH P P i P P C 3 Pyrophosphate C OH Nucleoside triphosphate 2 P i 5 5

Overall directions of replication Figure 16.15 Overview Leading strand Lagging strand Origin of replication Primer Leading strand Lagging strand Origin of replication Overall directions of replication 3 5 5 RNA primer 3 3 Sliding clamp DNA pol III Parental DNA 5 Figure 16.15 Synthesis of the leading strand during DNA replication. 3 5 5 3 3 5

Overall directions of replication Figure 16.16 3 Overview 5 Template strand 3 Leading strand Origin of replication Lagging strand RNA primer for fragment 1 5 3 Lagging strand 2 1 5 Leading strand 1 3 Overall directions of replication 5 3 Okazaki fragment 1 5 1 RNA primer for fragment 2 3 5 5 Okazaki fragment 2 3 2 1 3 5 5 Figure 16.16 Synthesis of the lagging strand. 3 2 1 3 5 5 3 2 1 3 5 Overall direction of replication

Overall directions of replication Figure 16.16a Overview Leading strand Origin of replication Lagging strand Lagging strand 2 1 Leading strand Figure 16.16 Synthesis of the lagging strand. Overall directions of replication

3 5 3 Template strand 5 Figure 16.16b-1 Figure 16.16 Synthesis of the lagging strand.

RNA primer for fragment 1 Figure 16.16b-2 3 5 Template strand 3 5 3 RNA primer for fragment 1 5 1 3 5 Figure 16.16 Synthesis of the lagging strand.

RNA primer for fragment 1 Figure 16.16b-3 3 5 Template strand 3 5 3 RNA primer for fragment 1 5 1 3 5 3 Okazaki fragment 1 5 1 3 5 Figure 16.16 Synthesis of the lagging strand.

RNA primer for fragment 1 Figure 16.16b-4 3 5 Template strand 3 5 3 RNA primer for fragment 1 5 1 3 5 3 Okazaki fragment 1 5 1 RNA primer for fragment 2 3 5 5 3 2 Okazaki fragment 2 1 3 5 Figure 16.16 Synthesis of the lagging strand.

RNA primer for fragment 1 Figure 16.16b-5 3 5 Template strand 3 5 3 RNA primer for fragment 1 5 1 3 5 3 Okazaki fragment 1 5 1 RNA primer for fragment 2 3 5 5 3 2 Okazaki fragment 2 1 3 5 Figure 16.16 Synthesis of the lagging strand. 5 3 2 1 3 5 5 3

RNA primer for fragment 1 Figure 16.16b-6 3 5 Template strand 3 5 3 RNA primer for fragment 1 5 1 3 5 3 Okazaki fragment 1 5 1 RNA primer for fragment 2 3 5 5 3 2 Okazaki fragment 2 1 3 5 Figure 16.16 Synthesis of the lagging strand. 5 3 2 1 3 5 5 3 2 1 3 5 Overall direction of replication

Overall directions of replication Figure 16.17 Overview Leading strand Origin of replication Lagging strand Leading strand Lagging strand Overall directions of replication Leading strand 5 DNA pol III 3 Primer Primase 3 5 3 Parental DNA Figure 16.17 A summary of bacterial DNA replication. DNA pol III Lagging strand 5 DNA pol I DNA ligase 4 3 5 3 2 1 3 5

Lagging strand template 3 5 DNA pol III Lagging strand 3 5 Figure 16.18 DNA pol III Parental DNA Leading strand 5 5 3 3 3 5 3 5 Connecting protein Helicase Lagging strand template 3 5 Figure 16.18 A current model of the DNA replication complex. DNA pol III Lagging strand 3 5

5 3 3 5 Nuclease 5 3 3 5 DNA polymerase 5 3 3 5 DNA ligase Figure 16.19 5 3 3 5 Nuclease 5 3 3 5 DNA polymerase 5 3 Figure 16.19 Nucleotide excision repair of DNA damage. 3 5 DNA ligase 5 3 3 5

Ends of parental DNA strands Lagging strand 3 Figure 16.20a 5 Leading strand Ends of parental DNA strands Lagging strand 3 Last fragment Next-to-last fragment RNA primer Lagging strand 5 3 Parental strand Figure 16.20 Shortening of the ends of linear DNA molecules. Removal of primers and replacement with DNA where a 3 end is available 5 3

Second round of replication Figure 16.20b 5 3 Second round of replication 5 New leading strand 3 New lagging strand 5 3 Figure 16.20 Shortening of the ends of linear DNA molecules. TTAGGG repeats = telomeres (100 to 1000 tandem repeats) Further rounds of replication Shorter and shorter daughter molecules

Figure 16.21 Figure 16.21 Telomeres. 1 m

Nucleosome (10 nm in diameter) Figure 16.22a Nucleosome (10 nm in diameter) DNA double helix (2 nm in diameter) H1 Histone tail Figure 16.22 Exploring: Chromatin Packing in a Eukaryotic Chromosome Histones Nucleosomes, or “beads on a string” (10-nm fiber) DNA, the double helix Histones

Replicated chromosome (1,400 nm) Figure 16.22b Chromatid (700 nm) 30-nm fiber Loops Scaffold 300-nm fiber 30-nm fiber Figure 16.22 Exploring: Chromatin Packing in a Eukaryotic Chromosome Replicated chromosome (1,400 nm) Looped domains (300-nm fiber) Metaphase chromosome

Figure 16.UN04 Figure 16.UN04 Test Your Understanding, question 10