Bacterial Genetics Flashcards
3 ways of passing genetic information between bacterium
- Conjugation
- Transformation
- Transduction
Conjugation (general)
involves the transfer of DNA from a donor cell to a recipient cell through a sex pilus
Transformation (general)
involves the transfer of genetic information by naked extracellular DNA
Transduction (general)
involves the transfer of genetic information to a bacterium from a bacteriophage or between bacterial or yeast cells mediated by a phage vector
Why do we use an agar plate vs. a liquid growth medium?
agar plate allows us to tell the cells apart and quantify/isolate colonies
Minimal media
synthetic culture that contains only the material essential for the growth of a WT organism
Prototrophs
any strain of microorganism that can grow in solely minimal media
Auxotrophs
any strain of microorganism that differ from the WT strains and cannot grow on minimal media
Lederberg and Tatem experiment
two strains of bacteria that were each unable to synthesize DIFFERENT proteins were combined
together, the two auxotrophs were able to produce prototrophs
shows that genetic exchange occurred between the two strains (highly unlikely that this occurs by chance alone)
What direction does conjugation occur in?
unidirectional transfer of genetic material
from F+ (or HFr) to F-
Davis U-Experiment 1
Medium can pass back and forth between cells, but the cells cannot
No prototrophs were generated
Shows that direct contact is needed for conjugation to occur
F-pilus
hairlike tubular structure that allows for bacterial conjugation between 2 cells
Basic steps of conjugation
- F+ has a F-factor plasmid that encodes for the formation of the F-pilus
- Endonuclease enzyme separates the 2 strands of the F-factor plasmid
- One strand moves across the plasmid
- Separated plasmid strands are replicated in each cell
- Ligase closes the two circles
(now both cells have the ability to code for the F-pilus)
Wollman and Jacob
mixed HFr and F- strains and used interrupted mating technique to map genes by time
shows that genes were transferred at different points of entry and in different directions
proposed that DNA is circular
Difference between F+ cell and Hfr cell
F+ cell has an F-factor plasmid that can be passed
Hfr cell has F-factor plasmid integrated into the main chromosome as the point of origin