Introduction to Genetic Analysis 158

Introduction to Genetic Analysis 158 - 157 5.2 Bacterial...

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Unformatted text preview: 157 5.2 Bacterial conjugation Donor F + Plasmid Pilus Bacterial chromosome (a) (b) Recipient F Figure 5-7 Conjugation. (a) During conjugation, the pilus pulls two bacteria together. (b) Next, a bridge (essentially a pore) forms between the two cells. A single-stranded copy of plasmid DNA is produced in the donor cell and then passes into the recipient bacterium, where the single strand, serving as a template, is converted to the double-stranded helix. F Integrated F Hfr F 1 Figure 5-8 Formation of an Hfr. Occasionally, the independent F factor combines with the E. coli chromosome, creating an Hfr strain. The F plasmid directs the synthesis of pili, projections that initiate contact with a recipient (Figure 5-6) and draw it closer. The F DNA in the donor cell makes a single-stranded copy of itself in a peculiar mechanism called rolling circle replication. The circular plasmid rolls, and as it turns, it reels out the single-stranded copy like fishing line. This copy passes through a porecopy like fishing line....
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