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Bacterial Genetics
1. Bacterial Genetics
Jaime A. Santos, MD,FPPS,FPIDSP
Friday, October 9, 2009
2. Bacteria: Prokaryotes
• nucleoid : not enclosed by
nuclear membrane
• most have one circular
chromosome consisting of
double-stranded DNA
• single origin of bidirectional
replication
Friday, October 9, 2009
3. Plasmid
plasmid
chromosome
Friday, October 9, 2009
9. Mutation
• 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)
Friday, October 9, 2009
10. Mutation: effect on protein product
• 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
Friday, October 9, 2009
13. Genetic Exchange in
Bacteria
•Transformation
•Transduction
•Conjugation
Friday, October 9, 2009
14. Genetic Exchange: Transformation
• incorporation of exogenous or
foreign DNA
• competence - ability to interact
with exogenous DNA
• H. influenzae, S. pneumoniae,
Neisseria
Friday, October 9, 2009
17. Bacteriophages
• viruses infecting bacteria
• bacteriophage infection may
result in lysis (by virulent
phages) or lysogeny (by
temperate phages)
Friday, October 9, 2009
20. Genetic exchange: Transduction
• transfer of bacterial DNA from
one cell to another by means of a
bacteriophage infection
Friday, October 9, 2009
21. 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
Friday, October 9, 2009
22. Generalized
Transduction
Friday, October 9, 2009
23. Specialized
Transduction
Friday, October 9, 2009
24. Plasmids
• 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
Friday, October 9, 2009
25. 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
Friday, October 9, 2009
