Slide 17.1 DNA Is the Hereditary Molecule of LifeChromosomes Contain DNAEarly Suggestion That DNA Was the Hereditary MaterialFocus on the Nucleus and ChromosomesThe Transformation FactorGriffith’s Experimental ResultsSlide 8Experimental ResultsSlide 10DNA Is the Hereditary MoleculePhage Infection of BacteriaHershey and Chase ExperimentsSlide 14Slide 15DNA NucleotidesTwo Types of DNA BasesAssembly of Polynucleotide ChainsComplementary DNA Nucleotide PairingSlide 20Antiparallel OrientationThe Twisting Double HelixNucleotide Base StackingMajor and Minor Grooves7.3 DNA Replication Is Semi-conservative and Bi-directionalThree Attributes of DNA Replication Shared by All OrganismsThree Competing Models of ReplicationThe Three ModelsSlide 29The Meselson-Stahl ExperimentExperimental ResultsSlide 32Origin of Replication in Bacterial DNACairns’ ObservationsEvidence of Bidirectional DNA ReplicationSupport for Bidirectional ReplicationAdditional Support for Bidirectional ReplicationMultiple Replication Origins in EukaryotesCopyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachCHAPTER 7DNA Structure and ReplicationCopyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach7.1 DNA Is the Hereditary Molecule of Life2•“Hereditary molecule”: any molecular substance that carries and conveys genetic information.•Before DNA was known to be the hereditary molecule, five essential characteristics were identified1. Localized to the nucleus, component of chromosomes. 2. Present in stable form in cells.3. Sufficiently complex to contain information needed for structure development and reproduction.4. Able to accurately replicate itself so that daughter cells contain the same information as the parent cell.5. Mutable, undergoing a low mutations rate that introduces genetic variation and serves as a foundation for evolutionary change.Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachChromosomes Contain DNA•DNA was first noticed in 1869 when Friedrich Meischer isolated it from nuclei of white blood cells.•It was weakly acidic and phosphorous rich.•He called it “nuclein.”•In the 1870s, microscopic studies identified fusion of male and female nuclei during reproduction and chromosomes were observed soon after.3Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachEarly Suggestion That DNA Was the Hereditary Material4•In 1895, Edmund Wilson first suggested that DNA might be hereditary material.•He observed that sperm and eggs contribute the same number of chromosomes during reproduction. •He made a connection between the substance observed by Meischer and chromatin of chromosomes.•In 1900, Mendel’s hereditary principles were rediscovered.•In 1903, Sutton and Boveri independently described the parallels between chromosome portioning.Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachFocus on the Nucleus and Chromosomes5•By 1920, DNA was identified as the principle component of nuclein.•The basic chemistry of DNA was deciphered.•It is a polynucleotide consisting of four repeating subunits; A,T,C,G; bound by covalent bonds.•In 1923, DNA was localized to chromosomes and made a candidate for the hereditary material.•However, both proteins and RNA are also found in chromosomes.• Lipids and carbohydrates were also considered to be candidates.Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachThe Transformation Factor6•Frederick Griffith identified two strains of Pneumococcus: S, which caused fatal pneumonia in mice, and R, which did not.•A single nucleotide change can convert the R (rough) strain into the S (smooth) strain.•These strains occur in four antigenic types (I, II, III, and IV) that cannot be altered by mutation alone.roughsmoothCopyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachGriffith’s Experimental Results7•Mice infected with strain SIII developed pneumonia and died.•Mice infected with the strain RII or with heat-killed strain SIII survived.•Mice infected with heat-killed strain SIII and live strain RII developed pneumonia and died –live type SIII bacteria were recovered from the mice.•Griffiths had described the process of transformation.•Biochemical tests of the heat-killed SIII extract showed that it contained mainly DNA, with small amounts of RNA, proteins, lipids, and polysaccharides.•Further tests required to required to identify transforming material.Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach8Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachExperimental Results•Avery, MacLeod, and McCarty used heat-killed SIII bacteria and live RII bacteria and infected mice.•The extract of heat-killed SIII bacteria was divided into aliquots and treated to destroy either DNA, RNA, proteins, or lipids and polysaccharides.•All aliquots killed the mice except the one with the DNA destroyed.9Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated Approach10Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachDNA Is the Hereditary Molecule11•Hershey & Chase (1952) showed that DNA is responsible for bacteriophage infection of bacteria.•Bacteriophages are viruses that infect bacteria.•Phages such as T2 have a protein shell with a tail that attaches to the host cell and a head that contains DNA.•Phages must infect bacterial hosts to reproduce.•Infection begins when the phage injects DNA into the bacterial cell and leaves its protein shell on the surface.•The phage DNA replicates in the bacterium and produces proteins that are assembled into progeny phage – these are released by lysis of the host cell.Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachPhage Infection of Bacteria12Copyright © 2012 Pearson Education Inc. Genetics Analysis: An Integrated ApproachHershey and Chase Experiments13•Proteins contain large amounts of sulfur but almost no phosphorus; DNA contains large amounts of phosphorus but no sulfur.•Hershey and Chase separately labeled either phage proteins (with 35S) or DNA (with 32P) and then traced each radioactive label in the course of infection. •After infection, agitation by a blender separated the empty phage particles from the infected bacteria.•In the