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Bacterial Genetics
lecture 23 alto
| Question | Answer |
|---|---|
| episome | a plasmid that can integrate itself into the chromosome of a host organism |
| conjugation | exchange of genetic material btwn 2 cells via cell-to-cell contact |
| composite transposon | type of transposon that consists of a host gene, like one for abx resistance, flanked by insertion sequence |
| insertion mutation | refers to integration of foreign DNA into a host gene, thereby inactivating the host gene |
| lysogeny | a state in which the bacterial and viral genomes replicate synchronously in a virus-infected bacterium; virus genome is integrated into the bacterial genome |
| plasmids | autonomously replicating DNA molecules found in bacteria; may be transferred from cell to cell |
| replicon | any form of DNA that contains all elements necessary for replication; includes plasmids, chromosomal DNA and bacteriophages but NOT transposons |
| generalized vs specialized transduction | process for introduction of foreign genes into a cell using a plasmid general - any host gene has an equal chance of being transduced specialized - only the host gene adjacent to the phage DNA attachment site is transduced |
| homologous recombination requires _____ to align the sequences | Rec protein like RecA in E. coli |
| linear DNA incorporation requires 2 crossovers, but circular DNA only requires one | |
| T/F Nonhomologous recombination doesn't require RecA for DNA exchange. | True - no homology btwn sequences, so site-specific enzyme is needed to align the strands |
| site-specific recombination | requires site-specific enzyme or recombinase to perform crossover; no RecA needed circular DNA/plasmid incorporation = net gain of DNA |
| transposons | present in pathogenicity islands as seen by their different GC content, encode for virulence genes, include transposase for insertion in different parts of genome. contain inverted repeats at their ends, site-specific recombination |
| transformation | introduction of naked DNA into a recipient cell, which will incorporate it into its genome. usually encodes virulence factors, process is sensitive to DNAase |
| 3 bacteria that are naturally competent (take up linear fragments of DNA from donor bacteria in vivo) | N. meningitidis, S. pneumoniae, H. influenzae |
| conjugative vs non-conjugative plasmids | possess genes that allow transfer into other bacteria and are low in copy # vs those which cannot transfer themselves, are usually found in high copy #/cell |
| F plasmid | encodes for the F pilus and all the proteins that are involved in transferring the plasmid to another recipient |
| the F plasmid integrates into the bacterial chr using site-specific recombination to produce Hfr donor strains | |
| two fates for an Hfr donor bacterium | excises itself to form an F plasmid again; imprecise excision will result in genetic transfer b/c a part of the original genome is carried along Hfr can conjugate directly from chr into a recipient F- cell in a time-dependent fashion with high capacity |
| how do non-conjugative plasmids transfer to new cells? | they still have an origin of transfer (oriT), transfer factors on a separate helper plasmid allow it to be conjugated |
| conjugative transposon | has the ability to transfer itself from the donor to a recipient via conjugation either with a co-resident plasmid or not |
| transduction | refers to the ability of a phage to carry chromosomal DNA from an infected donor cell to a newly infected recipient cell |
| specific infecting phage of E. coli | T4 phage |
| 2 cycles of a phage | lytic - rapid accumulation of new phage particles and eventual destruction of the cell for release lysogenic - integration of phage genome into bacterial chr to form lysogen |
| damaged DNA, UV light, abx or heat (any stress) will move the lysogen into the lytic cycle | EHEC and Shigella become stressed when given abx and prophages begin to express toxins during lytic phase |
Created by:
sirprakes
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