Bacterial Genetics

Bacterial Genetics - Bacterial Genetics Conjugation o The...

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Bacterial Genetics Conjugation o The contact and fusion of two different cells o After fusion, one cell (donor) sometimes transfers DNA in one direction to the other cell o In some cases, the extragenomic DNA (plasmid) is transferred o Any genomic fragment transferred may recombine with the recipient’s chromosomes o Process 1. A donor cell extends one or more projections, or pili, that attach to a recipient cell and pull the two bacteria together 2. The plasmid DNA in the donor cell makes a single stranded copy of itself in a peculiar mechanism called the rolling circle replication 3. The circular plasmid rolls and as it turns it reels out the single stranded copy like fishing line 4. The copy passes through a pore in the recipient cell, where the other strand is synthesized forming a double helix 5. A copy of the plasmid remains in the donor and another appears in the recipient Graph shows time course of entry of each donor allele o The donor alleles appear in a specific sequence o later donor alleles are present in fewer recipient cells In the conjugating Hfr, single-stranded DNA transfer beings from a fixed point on
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the donor (O- Orgin) and continues in a linear fashion o O-origin is where the plasms F is insterted o The farther a gene is from O, the later it is transferred to the F- o The transfer process generally stops before the farther-most genes are transferred these genes are included in fewer exconjugants. Transformation o When one bacterial cell takes up a piece of DNA from the external environment and incorporates this DNA into its own chromosome If the DNA is of a different genotype fro mthat of the recipient, the genotype of the recipient can become permenantly changed
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Bacterial Genetics - Bacterial Genetics Conjugation o The...

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