醫(yī)學微生物學英文教學課件：第二章細菌的遺傳與變異 （七年制）

1、Chapter 2 Bacterial heredity and variation Concept:Heredity (inheritance) the “l(fā)ikeness” of the characteristics of progeny and parent.Variation the “ difference ” between progeny and parent. heritable variation: genetic substance changes . non-heritable variation : environment changes. variation exa

2、mples 1. Morphological and structure variation L form ; 2.Virulence variation Mycobacterium tuberculosis: BCG Bacillus diphtheriae: acquires the ability of producing toxin 3.Resistance variation drug-resistance 4.Colony shape variation S-R variation , H-O variation smooth colonyrough colony Genetic

3、substance Bacterial genomechromosomeplasmid transposable elementbacteriophage Plasmid Extro-chromosomal genetic substance. (binding to chromosome-episome ) Circle double strand DNA1. autonomous replication 2. control most of auxiliary functions of bacterial cell antibiotic resistance R plasmid . pro

4、duction of fimbriaeF plasmid bacteriocin E. coli con plasmid.3. dispensable, it can be lost . 4. transfer from a bacteria to another conjugative plasmid : F+ sex pilus non-conjugative plasmid: phage 5. Stringent plasmid and relaxed plasmid 6. Incompatibility and compatibility. Incompatibility compat

5、ibility Bacteriophage -bacterial virus (1) viral common properties smallest simple structure :DNA/RNA, protein parasite in living cell (2) widespread existence (3) high host specific parasites Biological properties Shape and structure Seen by EM: Tadpol, microsphere , slim rod core DNA/RNA collar he

6、ad tail coat pipe-like capsid protein base plate tail fibreTailHead/CapsidContractile SheathTail FibersBase Plate Bacteriophage T4 Bacteriophage phi 29 Bacteriophage p22 Filamentous Bacteriophages phage VS bacteria virulent phage replicate in cell and released in lysis of bacteriaAdsorption Penetrat

7、ion Biosynthesis Assembly and Release PhageBacteria+Phageplaque temperate phage infected bacterial phage does not replicate , its gene integrated with bacterial DNA, its replication is associated with bacterial DNA. Prophage- The DNA of temperate phage integrated into bacterial DNA. lysogenic phage

8、lysogenic bacteria prophagelysogenic bacteriatemperate phage溶菌性周期溶原性周期 噬菌體與細菌的相互作用 Transposable element a segment of DNA that can move from one site to other target sites in the same or different DNA molecule . (chromosome, plasmid and phage) insertion sequence (IS) inverted repeat + transposases tr

9、ansposon (Tn) IS+geneIS ISResistance Gene(s)IS ISResistance Gene(s)TransposaseABCDEFGGFEDCBAISTnThe mechanism of variation variation mutation genetic transfer base substitutionbase deletion base insertion TransformationTransduction Conjugation Lysogenic conversionProtoplast fusionMutation a stable h

10、eritable change of bacterial gene spontaneous 10-610-9 inducible - inductor reverse mutation wild strainmutant strainmutationreplica test (Ames test)mutation and selectiontype of mutation 1. base substitution transition : AG, CT transversion: AT CG2.base deletion lost 3.base insertion genetic transf

11、er Genetic substance of bacteria is transferred to another bacteria. Donor bacteria : provide genetic substance Recipient bacteria: accept genetic substanceTransformationTransformation recipient bacteria takes up exogenous DNA of donor bacteria. Competence bacterial state, in which bacteria can able

12、 to take up DNA from the environment in log. Phase.Transformation Conjugation bacterial DNA is transferred from donor bacteria to recipient bacteria by sex piliF plasmid sex pili Hfr F plasmid (high frequency recombination)F+Sex pili R plasmid Tn 9Tn 21Tn 10Tn 8RTFR determinantRTFConjugative plasmid

13、Transfer genesR determinantResistance genesTransposonsF+F-F+F-F+F+F+F+HfrF-HfrF-HfrF-HfrF-FFFFFF-FF-F plasmidTransduction Gene transfer from a donor to a recipient by way of a bacteriophage generalized transduction specialized transductiongeneralized transduction any fragment gene of donor bacteria is transferred. randomgeneralized transductionspecialized transduction the fragment gene near attachment site is t