Bacterial Gene Transfer & Plasmids Flashcards
What is transformation? A transformant? Competent bacteria?
process of horizontal gene transfer by which some bacteria take up foreign genetic material (naked DNA) from the environment
cell that has taken up recipient DNA by transformation
bacterial that are able to take up DNA naturally (without artificial treatment)
What is homologous recombination?
identical or similar regions of DNA align and exchange with each other by excision-repair
(AKA allelic exchange or strand replacement)
What are transformasomes? Transfection? Complementation?
compartment that has take up double-stranded DNA
uptake of viral DNA
mutated DNA expressed on a plasmid (in trans) will correct the mutation
How does transformation happen? How does the strandedness of DNA affect this process?
- DNA from donor cells is introduced into the recipient cell with plasmid DNA
- donor DNA enters the cell
- recombination between donor DNA and recipient DNA occurs, resulting in a genetically transformed cell
- unrecombinated DNA is degraded
only dsDNA can bind to cells and only ssDNA can be taken up
How can competence be induced? What does this allow?
Ca2+ treatment or electroporation
allows cell to take up dsDNA as well as ssDNA and circular plasmids
What 3 discoveries were made based on transformation?
- evidence that DNA was the material responsible for the transfer of pathogenic determinants (genes)
- provided an explanation as to how bacteria can acquire other genes
- provided the basis for the development of artificial transformation schemes (electroporation)
What 2 things does artificial transformation schemes allow for?
- introduce foreign genes into both eukaryotic and prokaryotic cells
- allowed for the easy production of mutants to allow for the definition of gene function (virulence determinants)
Bacteriophage structure:
What is transduction?
the process of transferring DNA from one bacterium to another by a phage
What are the lytic and lysogenic phases of transduction?
LYTIC: virus penetrates through the penetration of the cell membrane and DNA replication process
LYSOGENIC: virus fuses its DNA with the host.
Why is the lysogenic cycle of transduction significant?
host cell does not lyse, allowing phage DNA to integrate into and replicate in the host cell DNA, which can pass along virulence factors (antibody/complement resistance, toxigenicity)
What are prime factors? What are 3 types?
extrachromosomal pieces of DNA (mini-chromosomes) that autonomously replicate independently of chromosomes
- PLASMIDS: genes of unknown origin and often not necessayr for growth; may code for virulence factors
- F-FACTOR: fertility factor; genes promote replication and transfer of the factor to recipient cells (conjugation)
- R-FACTOR: resistance factor; F-factor + genes encoding resistance to specific antibiotics
What is conjugation?
major horizontal gene transfer mechanism through which DNA is transferred from a donor to a recipient bacterium by direct contact (between 2 bacteria)
What 2 types of genes are present in R-factor plasmids?
- resistance transfer factor (RTF) = encodes origin of replication, sex pili genes
- R-determinants = genes encoding antibiotic resistance or other virulence factors and insertion sequences (IS)
What are transposons (Tn)?
“jumping genes” that are mobile genetic elements able to move from one region of a chromosome or plasmid to another (10^-5 to 10^-7 per generation)
Transformation vs conjugation vs transduction:
