microbial genetics Flashcards
what is horizontal gene transfer
genes are passed laterally from one mature prokaryote to another
what type of organisms can undergo HGT
prokaryotes
what is a recombinant organism
one that has characteristics of both the donor and recipient
what is the main method of genetic diversity among prokaryotes
HGT
what types of DNA can be transferred in HGT
a DNA fragment or a plasmid
list the 3 methods in which HGT can occur
conjugation, transformation, transduction
what are the 2 possible fates for HGT
either you get stable recombinants or no stable recombinants
what 2 ways can we get stable recombinants due to HGT
if the DNA is integrated into the host chromosome or if the donor DNA self replicates into a plasmid
what 2 ways do we get no stable recombinants due to HGT
when the donor DNA cannot self replicate, or when there’s degradation of donor DNA
define conjugation
transfer of genetic material from a donor cell to a recipient cell via direct contact
what is conjugation mediated by
the F plasmid
what does the F plasmid stand for
fertility plasmid
how many stands do plasmids have
2
shape of plasmids?
linear or circular
do plasmids have lots of few genes
few
describe the importance of plasmids in regards to the host genome
plasmids are seen as “extra” for the host
describe the number of copies that plasmids can exist as
can be single or multicopy
define episome
a plasmid that can exist with or without being incorporated into the host’s chromosome
T or F: the F plasmid is an episome
true
what are cells that carry the F plasmid called
F+ (donor)
what are cells that lack the F plasmid called
F- (recipient)
what do F+ cells produce to aid in conjugation
sex pili
what type of bacteria is the F plasmid found in
only gram negative
T or F: the F plasmid is found in all types of bacteria (both gram neg and pos)
false; only gram negative
describe conjugation briefly
donor cell protrudes the sex pilus and contact is made with the recipient cell. F plasmid goes through the sex pilus into the recipient cell and then the pilus retracts
in terms of F+ and F-, describe the final result of an F+ cell conjugating with an F- cell
both cells become F+
describe how the F plasmid can be incorporated onto the recipient’s chromosome
plasmid contains sequences that are homologous to sequences on the chromosome, thus homologous recombination can occur (plasmid insertion)
what is homologous recombination
plasmid integrates into the host’s chromosome due to homologous sequences
what is an Hfr cell (how is it made)
made when a bacterium gets the F plasmid integrated into it’s chromosome
where is the plasmid DNA from the donor located in an Hfr cell
plasmid DNA has been incorporated into the chromosome
what does Hfr stand for
high frequency of recombination
what happens when an Hfr cell and F- cell conjugate
the chromosome breaks before the entire thing has transferred and the F plasmid is not transferred. F- remains as such, though it can contain new chromosomal genes
result of Hfr x F-
Hfr and F-
T or F: an integrated F plasmid may hop out of the Hfr chromosome
true
what can happen when the integrated F plasmid hops out of the Hfr chromosome
a mistake in excision may occur, and it may carry some of the donor’s chromosomal genes with it
what is produced when the integrated F plasmid leaves the Hfr chromosome + takes donor genes with it
we get F’ (F prime)
what do we get when F’ x F-
F’ and F’
T or F: conjugation can occur in both gram neg and gram pos bacteria
true; but there are some differences
list 1 difference in gram pos conjugation vs gram neg conjugation
gram pos conjugation does not involve a sex pilus
define transformation
the uptake of DNA from the environment
what two forms of DNA can be used in transformation
DNA fragment or a plasmid
what are competent cells
a cell that’s in a physiological state in which it can uptake donor DNA
in what environments might transformation occur (4)
soil, water, in vivo, biofilms
how does transformation work
a pilus extends into the environment and retracts back into the cell when it contacts DNA
are E coli cells naturally competent
no
how are e coli cells made competent in the lab
heat shock with CaCl or electrical shock via an electroporator
define transduction
the mechanism by which bacterial genes are transferred from one bacterium to another via a bacteriophage
what are bacteriophages
viruses that infect bacteria
list the 2 types of bacteriophages
virulent or temperate
what do virulent phages do/what do they do to the bacteria
they lyse the bacterial cell
what do temperate phages do/what do they do to the bacteria
- can reproduce lytically
- can integrate into the host’s chromosome + remain with it without destroying the bacterial cell
what is the viral genome called once the temperate phage has integrated into the host’s chromosome
prophage
what is the name for the bacterium that’s harboring the temperate phage
lysogen
go through the steps of the lytic cycle
phage injects DNA into host cell’s cytoplasm. This directs the synthesis of many new phages, then cell lyses and releases the new pathogens/phages. the phages can then bind to other cells
go through the steps of the lysogenic cycle
phage injects DNA into cell and then the DNA is integrated into the host chromosome. Prophage DNA is copied when the cell divides. Exposure to stress (ie UV light) triggers excision from the host chromosome, and now the host chromosome is pure again
what temperate phage infects e coli
bacteriophage lambda
what are the two types of transduction
general and specialized
when does general transduction occur (what cycle)
during the lytic cycle
what types of phages use general transduction
both virulent and temperate
describe general transduction
random pieces of DNA are transferred from one bacterium to another via a phage. Any piece of the host’s chromosome can be transferred = generalized
when does specialized transduction occur
when there is an error in the life cycle of a temperate phage
why is specific transduction called specific
only specific pieces of DNA from the host will be transferred to the recipient via a phage
describe how HGT can be responsible for the spread of antibiotic resistance
microbes that synthesize antibiotics must have resistance genes. these genes are spread via HGT to other cells, giving them resistance too. OR spontaneous mutations may occur but less likely
