Paper I — 2013 September (Supplementary) (2010 Scheme) — Q8
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Paper I
2013 September (Supplementary) (2010 Scheme) · 40 marks · 120 min
Question
Bacterial conjugation.
Q82 marksShort Notes
Answer
Bacterial conjugation is a mechanism of horizontal gene transfer in which genetic material (typically a plasmid, e.g., the F plasmid or an R plasmid) passes from a donor to a recipient bacterial cell through direct cell-to-cell contact, mediated by a specialized surface appendage called the sex pilus (F pilus).
Mechanism: a donor cell carrying the fertility (F) plasmid (F⁺ cell) extends its sex pilus to make contact with and draw a recipient (F⁻) cell close; a conjugation bridge/pore forms between the two cells; a single strand of the plasmid DNA is nicked at the origin of transfer and transferred through the bridge into the recipient, where it is replicated to double-stranded form — the recipient is thereby converted into an F⁺ cell (in simple F-plasmid transfer, the bacterial chromosome itself is not transferred).
Hfr conjugation: when the F plasmid integrates into the bacterial chromosome (forming an Hfr — high frequency of recombination — strain), conjugation can transfer part of the donor’s chromosomal DNA along with it, allowing chromosomal gene transfer and recombination in the recipient.
Clinical significance: conjugation is the principal mechanism by which R (resistance) plasmids, carrying multiple antibiotic-resistance genes, spread rapidly between bacteria (even across different genera), driving the emergence and dissemination of multidrug-resistant organisms — a major concern in hospital-acquired infections.
