ch 6 the genetics of bacteria and their viruses Flashcards
characteristics of bacteria
- single celled
- prokaryotic (no membrane-bound organelles)
- have only 1 circular chromosome
minimal medium
medium containing only inorganic salts, a carbon source, and water
prototroph
a microorganism capable of growing on minimal medium (wild type)
auxotroph
a microorganism that will only grow on medium supplemented with a specific compound (not required by the wild type)
selective medium
only certain genotypes are able to grow
eg. minimal media selects against auxotrophs
differential medium
genotypes can be distinguished from each other based on how the organism grows on the medium
eg. staining of cells able to utilize lactose
3 mechanisms of DNA exchange in bacteria
conjugation
transformation
transduction
conjugation
the union of bacterial cells during which genetic info is transferred from donor (F+ or Hfr) to recipient (F-)
- requires cell to cell contact
transformation
introduction of foreign DNA material through external application; exchange of genetic info btw bacteria and environment
- uptake of ‘naked’ DNA
transduction
movement of genetic material from donor to recipient through a bacteriophage vector
- bacteriophage injection
is transfer of info directed?
yes, one strain is the donor and the other is the recipient
F (fertility) factor
bacterial episome (present on plasmid or chromosome) which allows a bacterial cell to be the donor during conjugation
plasmid
extrachromosomal, autonomously replicating, circular DNA
properties of the F-factor
- enables the production of the pili (proteinaceous attachment tube btw cells)
- able to replicate (cell division and conjugation)
- prevents conjugation between F+ cells
Hfr (high frequency of recombination)
a bacterial cell in which the F factor is integrated into the chromosomes; during conjugation, the F factor acts as the origin of chromosomal transfer
exconjugate
a bacterium that has undergone conjugation
endogenate
the endogenous recipient chromosome
exogenate
the exogenous donor chromosome
merozygote
a cell which is a partial diploid, containing both an endogenote and an exogenote
interrupted mating experiment
- allow two strains to conjugate
Hfr strain and F- strain - samples taken at specific time intervals and conjugation is interrupted
- plate on medium with streptomycin (inhibits HFR, only want to see growth of F- strain) and score for ton r, lac, gal, azi r
results of interrupted mating experiment
genetic markers appear in the exconjugates at specific times
- there is a fixed point at which transfer begins (origin), and a linear order to the transfer of markers
- time taken to transfer is related to the distance btw the marker and the origin of transfer
origin of transfer
the fixed point from which DNA transfer begins during conjugation
the F integration site determines
the order of marker transfer from Hfr
- relative position of markers is constant
three things mapping by minutes tells us
- order of transfer - linear arrangement of genes
- time of transfer - proportional distance btw genes
- can also determine position and orientation of the origin
gradient of transfer
genes nearest origin are transferred at a higher frequency than those farthest from the origin
- where you plateau is related to where you enter the cell
what happens to linear DNA in bacteria
it degrades
increasing conc of DNA results in
a higher frequency of transformation
higher co-transformation frequency =
closer to selected marker
bacteriophage
“bacteria eater”
a virus that infects bacteria
have a nucleic acid and protein coat
lytic cycle
mode of infection in which the bacteriophage genome enters the bacterium, replicates, lyses the cell, and progeny are released
virulent bacteriophage
a bacteriophage which always completes the lytic cycle upon infection (unable to become a prophage)
prophage
a phage genome which is integrated into a bacterial chromosme
lysogenic bacterium
bacterial cell capable of spontaneous lysis due to the release of a prophage from the bacterial chromosome
lysogenic
the state of a bacterial cell that has a prophage integrated into its chromosome
temperate bacteriophage
a phage capable of entering the lysogenic cycle with its host
generalized transduction
faulty head-stuffing
specialized transduction
faulty outlooping
- results in phage with chromosomal DNA
- requires lysogenic cycle
