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33 Cards in this Set
- Front
- Back
What are the three means by which genetic information can be transferred from one bacterium to another
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Transformation (uptake of foreign DNA), transduction (Bacteriophage), conjugation (cell to cell contact)
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If the transferred donor DNA is not itself a replicon, and therefore cannot replicate in the recipient bacterium, what must happen
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Recombination between the donor DNA and the recipient genome is required to produce stable recombinant progeny
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What does recombination in bacteria refer to
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The replacement of one allele with another, rather than reassortment of two parental alleles as in a diploid organism
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How is DNA taken up by a bacteria
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1. Double stranded DNA molecules bind to specific receptors on recipient cells and are taken up by the recipient
2. One of the strands is degraded by an exonuclease 3. Single strand is integrated into the recipient chromosome by strand displacement and recombination |
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Which bacteria take up only DNA from their own species
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Haemophilus influenzae and Neisseria gonorrhoeae. Uptake requires the presence of a specific sequence of about 10 nucleotides
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What is transduction
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Transfer of genetic material from one cell (the donor) to another (the recipient) via a bacterial virus as vector
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What are the stages of the growth cycle of a virulent phage
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1. Adsorption (highly specific interaction between phage attachment protein and phage receptor on bacteria)
2. Penetration of nucleic acid (separation of phage nucleic acid from capsid) 3. Viral reproduction (gene transcription, maturation, release) |
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For a temperate phage, what is the vegetative cycle
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Similar to the lytic cycle
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For a temperate phage, what is the prophage stage
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Persistence of phage genome in host cell for many generations
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What is a lysogen
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A bacteria that is carrying prophage
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What does integration of phage DNA in bacterial chromosome require
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Lambda genes, such as integrase
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In relation to bacteriophages, what is repression
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Tighly controlled shutoff of extraneous genes of the phage vegetative (replicative) cycle.
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For lambda phage, what is the only phage gene transcribed
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The cI gene, which encodes the phage repressor, a cytoplasmic protein which binds to double stranded DNA of the prophage
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Lysogens are immune to infection by the same phage. How?
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Immunity is due to repressor acting on incoming phage DNA. Different phages make different repressors so immunity is specific
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What is generalized transduction
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Tranducing particles are produced during lytic infection of the donor cells by the transducing bacterial virus. In rare cases, random fragments of the donor host genome are packaged into the viral capsid in lieu of the virus genome
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What is abortive transduction
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The donor DNA is not integrated (recombined) into the recipient genome and is only passed linearly on to daughter cells
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What are specialized transducing phages
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They contain hybrid DNA molecules with genes from both the bacterial host and the temperate phage. They are produced by an anomalous excision of the prophage
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What is lysogenic conversion
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A consequence of lysogeny where phages can contribute new genetic characteristics to their host
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What is conjugation
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Transfer of genetic material from one cell (donor) to another (recipient) via a direct cell-to-cell contact
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What is Hfr mating type (High frequency recombination)
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The F factor can be stably integrated into the chromosome, resulting in the formation of an Hfr
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What is F'
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The F factor can be excised from the chromosome. Anomalous excision gives rise to an F' factor which is a hybrid DNA molecule carrying both F factor genes and bacterial genes
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What is the fate of transferred DNA from Hfr donors
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Donor DNA must recombine into recipient genome if it is to be stably inherited
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What is homologous recombination
What is required for it to occur in E. coli |
Reciprocal exchange between donor and recipient DNA that are homologous in nucleotide sequences. In E. coli, the recA gene is required
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What is site-specific recombination
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Breakage and rejoining at specific sites of the donor and recipient DNA molecules
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What are plasmids
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Extrachromosomal genetic elements. They have their own origins of replication, but require host enzymes for their replication and for expression (transcription and translation) of the genes located on the plasmids
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What are resistance plasmids (R factors)
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Plasmids that contain genes responsible for antibiotic resistance
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What are the two functionally distinct parts of R factors
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Resistance determinant (R determinant) and Resistance transfer factor (RTF)
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What are transposable elements (transposons)
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Elements that can move from one site to another site within a genome or between two genomes. R-determinants are an example
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What is transposition
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Process that does not require homology between the donor site and the recipient site and is independent of the RecA protein. Sequence specific enzymes (transposases) are required for this process
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What are insertion sequences
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They carry the gene for transposase, the enzyme that catalyzes transposition.
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What are the two types of transposition
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Cut and paste (direct or non-replicative); Replicative (formation of a co-integrate)
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What is the consequence of the insertion of an insertion sequence
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Insertion sequence (IS) may affect the expression of the gene into which it is inserted. It may also provide a new promoter for the gene downstream of the insertion site. They can therefore act as switches for turning a gene on or off
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What are transposons (or Tn elements)
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Larger than IS elements. In addition to a gene encoding transposase, they often contain genes unrelated to insertion function
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