Powerpoint 26 Flashcards
Bacteria use three different mechanisms to adapt to changing environments
- regulation of gene expression
- Mutation
- Gene transfer*
Genes are naturally transferred between bacteria using 3 mechanisms
- DNA-mediated transformation
- Transduction
- Conjugation
S. pneumoniae exsists in two forms
1) ecapulated, virulent-smooth
2) non-encapsulated,avirulent -rough
wondered if injections with the heat killed smooth strain could be used as a vaccine against pneumonia
-injected mice with the different strains and recorded results
Griffith
involves the transfer of naked DNA from the environment to the recipient cell
DNA-mediated transformation
cells rupture during the stationary and death phase
-the chromosome breaks into small pieces and explode trhough the ruptured cell wall
DNA-mediated transformation
recipient cell picks up piece of the naked DNA and the naked DNA is integrated onto the recipient chromosome
-replaces he homologous gene on the chromosome of the recipient cell
DNA-mediated transformation
atural transformation occurs when bacterial cells are-_____
competent
Bacterial cells are capable of taking up and integrating larger fragments of DNA. Competence occurs during…?
The late log, early stationary phase
Natural transformation occurs in 4 stages.
- entry of the DNA
- Integration of the donor DNA
- Mismatch repair
- cell multiplication
only single strands enter, double strands are degraded
entry of the DNA
Donor DNA is integrated by hydrogen bonding
- enzymes cleave recipient DNA
- Donor DNA is put in place
Integration of the donor DNA
- repair mechanism remove either donor or recipient DNA that doesnt match
- repairs with correct nucleotides
Mismatch repair
transformed cells multiply under selective conditions in which non-transformed cell will not grow
cell multiplication
Some, but not all bacteria have the ability to take up naked DNA.. What are some gram pos and gram neg ones that do
- some gram + e.g. Streptococcus, Bacillus
- some gram - are Nesseria, Haemophilus
_____ and ____ lack the machinery and can only be transformedartificially: chemicly competent or electro-competent
E.coli and Salmonella
Cytoplasmic membrane translocase system
Gram positive DNA-meadiated transformation
- competence is induced in growth phase dependent way by excreted peptide
- can be promiscuous: i.e. taking up all available DNA
Gram positive DNA- mediated transformation
added barrier of OM
Gram negative DNA-mediated transformation
-Pilis mediated transformation in
Nesseria
-Gram negative DNA-mediated transformation
most exhibit specific uptake, mediated by nucleotide sequence recognition
Gram negative DNA-mediated transformation
To slow the uptake of foreighn DNA, particulartly evading bacterial viruses
- avoid unnecessary incorporation of foregn DNA
- Imperfect to allow genettic melleability
- organisms have enzymes able of cutting DNA
what are the organisms able to cut DNA
Restriction endonucleases or restriction Enzymes
- recognize nucleotide sequence( 4bp, 6bp, or 8bp)
- can cut recognition sequence or certain distant away from recognition site
- avoid slowed activity by methylation
