Lecture 32 Gene Transfer in Bacteria Flashcards
What are three mechanisms of genetic transfer?
transformation, conjugation, and transduction
Horizontal Gene Transfer (HGT)
genetic exchange between organisms of the same generation
Why is horizontal gene transfer helpful?
allows bacteria, which typically have only one chromosome (haploid), to gain genetic diversity
Transformation
a genetic transfer process by which free DNA is incorporated into a recipient cell and may bring about genetic change
Competent
a cell that is able to take up DNA and be transformed
How can we induce cells to be competent?
by using calcium chloride or by electroporation
What does electroporation do?
causes temporary holes in cell wall/cell membrane
What confirmations of DNA can transformation occur with?
DNA fragments and plasmids
When DNA fragment uptake occurs, what are the two possible outcomes?
1) the fragment is integrated by nonreciprocal recombination –> stable transformation
2) degradation of the fragment –> unsuccessful transformation
Plasmids
independently replicating elements of double stranded DNA
Are plasmids helpful for bacterial cells?
usually are non-essential genes but can be very helpful in the right conditions
True or False: Multiple plasmids per cell cannot occur
False!
Dissimilation plasmids
plasmids that encode enzymes for catabolism of unusual elements
Resistance factors
plasmids that encode resistance to various elements (for example, antibiotics or metals)
Virulence plasmids
plasmids that increase pathogenicity
Conjugative or F plasmids/F factors
plasmids that carries genes for sex pili and transfer of plasmids
Components of F plasmids
1) mobile genetic elements/jumping genes
2) tra region (transfer region)
In conjugation, what is a donor cell?
the bacteria with the F plasmids (male), termed F+
In conjugation, what is an acceptor/recipient cell?
the bacteria with no plasmids (female), termed F-
How does bacterial conjugation begin?
sex pilus draws F- cell closer, inducing mating bridge to form
Mating bridge
the region of contact between the donor and recipient cells where the DNA is transferred via a pore
Hfr cell
high frequency of recombination cell; when the F plasmid recombines with the chromosome
What happens when an F- cell goes through recombination with an Hfr cell?
the F- cell may acquire new versions of chromosomal genes; remains an F- cell because it did not receive the complete F factor
Lytic cycle
the virus replicates and lyses cell; many reproduced
Lysogenic cycle
viral DNA is incorporated into host DNA; replication is delayed
Prophage
viral genome integrated into host DNA (hides out)
Transduction
the transfer of bacterial genes by viruses
When does generalized transduction occur?
during the lytic cycle of viruses
Generalized transduction
when random fragments of DNA from partially degraded host chromosomes are packaged by mistake
What does generalized transduction use to infect another host?
transducing particles
When does specialized transduction occur?
during the lysogenic cycle of viruses
Specialized transduction
when only specific regions of chromosome located near attachment site are transduced
What does the traducing particles carry during specialized transduction?
both bacterial chromosomal DNA and phage DNA
Mobile Genetic Elements (MGEs)
discrete segments of DNA that move as units from one location to another within other DNA molecules and can therefore also bring about genetic change
Insertion sequences
insert into another part of the genome
Transposons
sequences of DNA that move around to different positions within a genome and utalize insertion sequences
Are insertion sequences or transposons larger?
transposons
What enzyme do insertion sequences and transposons encode for?
transposase enzyme
What do transposons also carry (besides transposase)?
many genes such as antibiotic resistance
