武汉大学：《遗传学》课程教学课件（英文讲稿）Chapter 06 DNA Structure, Replication, and Recombination

Chapter 6 DNA Structure, Replication, and Recombination 6-1

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 6-1 DNA Structure, Replication, and DNA Structure, Replication, and Recombination Recombination Chapter 6

Sections to study6.1 ExperimentalevidenceforDNA as thegeneticmaterial6.2TheWatsonandCrickdoublehelixmodelofDNA6.3 Genetic information in DNA base sequence6.4DNAreplication6.5Recombination attheDNAlevel6-2

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 6-2 Sections to study Sections to study 6.1 Experimental evidence for DNA as the genetic 6.1 Experimental evidence for DNA as the genetic material material 6.2 The Watson and Crick double helix model of DNA 6.2 The Watson and Crick double helix model of DNA 6.3 Genetic information in DNA base sequence 6.3 Genetic information in DNA base sequence 6.4 DNA replication 6.4 DNA replication 6.5 Recombination at the DNA level 6.5 Recombination at the DNA level

The genetic material must exhibit four majorcharacteristicsStorage ofinformationExpression ofinformationReplicationVariation by mutationmutationReplicationGenesAllelesnew genesExpressionRaw materialsfor evolutionTraits6-3

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 6-3  Storage of information Storage of information  Expression of information Expression of information  Replication Replication  Variation by mutation Variation by mutation The genetic material must exhibit four major The genetic material must exhibit four major characteristics characteristics Genes mutation Alleles new genes Raw materials for evolution Traits Expression Replication

What are genes composed of ?Protein?20 different subunits-greaterpotentialvariety of combinationsChromosomes contain moreChromosomeNucleuscomereprotein than DNA by weightDNA ? Only four different subunits maup DNA.arCellChromosomes contain lessDNAthan protein by weightOther molecules?6-4

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 6-4 What are genes composed of ? What are genes composed of ?  Protein ? Protein ?  20 different subunits 20 different subunits – greater greater potential variety of combinations potential variety of combinations  Chromosomes contain more Chromosomes contain more protein than DNA by weight. protein than DNA by weight.  DNA ?  Only four different subunits make Only four different subunits make up DNA. up DNA.  Chromosomes contain less DNA Chromosomes contain less DNA than protein by weight. than protein by weight.  Other molecules ? Other molecules ?

6.1Experimental evidence forDNA asthegeneticmaterialUntil 1944, observations favored protein as the geneticmaterial.Proteins are abundant in the chromosomes.Proteins are well characterized chemicallyChromosomeNucleusslomereChemical stainingrevealed thatDNA isCentromerelocalizedalmostexclusively in thechromosomes.aicomaraCell6-5

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 6-5  Proteins are abundant in the chromosomes. Proteins are abundant in the chromosomes.  Proteins are well characterized chemically. Proteins are well characterized chemically. 6.1 Experimental evidence for DNA as 6.1 Experimental evidence for DNA as the genetic material the genetic material Chemical staining Chemical staining revealed that revealed that DNA is localized almost localized almost exclusively in the exclusively in the chromosomes. chromosomes. Until 1944, observations favored protein as the genetic material

Discovery ofDNA:1869-Friedrich Miescherextracted a weakly acidic,phosphorous-richmaterial from nuclei ofhuman white blood cellswhich he named nuclein6-6

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 6-6  1869 – Friedrich Friedrich Miescher Miescher extracted a weakly acidic, extracted a weakly acidic, phosphorous phosphorous-rich material from nuclei of material from nuclei of human white blood cells human white blood cells which he named which he named nuclein nuclein. Discovery of DNA: Discovery of DNA:

-NucleotideDNA-deoxyribonucleicacidFour nucleotide subunitslinked together byphosphodiester bondsDeoxyribosePolymersugarNitrogenous BasePhosphatePhosphodiesterbonds-NucleotideFig.6.2

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 6-7  DNA – deoxyribo eoxyribonucleic acid  Four nucleotide subunits Four nucleotide subunits linked together by linked together by phosphodiester phosphodiester bonds. Nitrogenous Base Fig. 6.2

Evidence favoringDNA as the genetic material was firstobtained during the study of bacteria and bacteriophagesTransformation studies:1928-FrederickGriffith published his experiment with smooth(S), virulent strain Streptococcus pneumoniae, and rough (R),nonvirulentstrainPolysaccharidecapsuleLivingRformRoughcolonySmoothcolonyLivingSformFig.6.36-8

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 6-8  1928 – Frederick Griffith Frederick Griffith published his experiment with smooth published his experiment with smooth (S), virulent strain (S), virulent strain Streptococcus Streptococcus pneumoniae pneumoniae, and rough (R), , and rough (R), nonvirulent nonvirulent strain. strain. Polysaccharide capsule Fig. 6.3 Transformation studies: Evidence favoring DNA as the genetic material was first Evidence favoring DNA as the genetic material was first obtained during the study of bacteria and obtained during the study of bacteria and bacteriophages bacteriophages

(b)InjectDeaMutatestoAliveInjectCellInjectHeat-killedcomponentsAliveCellHeat-killedcomponentsTissueanalyzedCombinedInjectDeadLiving SOrecoveredFig.6.46-9

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 6-9 Fig. 6.4

Conclusion from Griffith's experiment:Genetic information from dead bacterial cells could betransmittedto livecellsTransformation-One of the mechanisms that bacteriatransfer genes from one strain to another.Transformation occurred in the animal body6-10

Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 6-10  Genetic information from dead bacterial cells could be transmitted to live cells. Transformation – One of the mechanisms that bacteria transfer genes from one strain to another.  Transformation occurred in the animal body. Conclusion from Griffith’s experiment: