Bacterial Genetics

Bacterial GeneticsJaime A. Santos, MD,FPPS,FPIDSP

Friday, October 9, 2009

Bacteria: Prokaryotes• nucleoid : not enclosed by

nuclear membrane

• most have one circular chromosome consisting of double-stranded DNA

• single origin of bidirectional replication


Plasmid

plasmid

chromosome


DNA Structure


DNA Replication


Transcription


Translation


DNA Repair


• definition: any change in the base sequence of DNA

• single base change: transition (purine replaced by purine, pyrimidine replaced by pyrimidine) or transversion (purine replaced by pyrimidine or vice-versa)

Mutation


• silent mutation: no change in amino acid in encoded protein

• missense mutation: different amino acid in protein product

• nonsense mutation: change results in stop codon e.g. TAG

Mutation: effect on protein product


Mutation


Transposons


•Transformation•Transduction•Conjugation

Genetic Exchange in Bacteria


• incorporation of exogenous or foreign DNA

• competence - ability to interact with exogenous DNA

• H. influenzae, S. pneumoniae, Neisseria

Genetic Exchange: Transformation


Transformation


• viruses infecting bacteria

• bacteriophage infection may result in lysis (by virulent phages) or lysogeny (by temperate phages)

Bacteriophages


Bacteriophage: Lytic cycle


Bacteriophage: Lysogeny


Genetic exchange: Transduction

• transfer of bacterial DNA from one cell to another by means of a bacteriophage infection


Transduction: types

• generalized transduction: random packaging of bacterial host cell DNA in phage capsid

• specialized transduction: when prophage genome is excised it drags adjacent bacterial genes resulting in hybrid phage-bacterial genome


Generalized Transduction


Specialized Transduction


• self-replicating, circular, double-stranded DNA

• carry genetic information for new bacterial properties e.g. virulence factors and antibiotic resistance

• may transfer from 1 cell to another (conjugative plasmids) or may stay within bacterial cell

Plasmids


Genetic exchange: conjugation

• contact between F+ donor with sex pilus (coded by F plasmid) and F- recipient

• unidirectional

• starts from 5’ end

• results in transfer of conjugative plasmid or plasmid with bacterial genes to which it is integrated


Conjugation


What are the consequences of genetic exchange in bacteria?


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Thank You!

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Bacterial Genetics

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