Conjugation involves the transfer of DNA between living bacteria that are in physical contact. Which option correctly reflects this process?

• A. rate of DNA exchange
• B. mutation of plasmid transfer
• C. uptake of naked DNA from environment
• D. transfer of DNA between living bacteria that are in physical contact (F-plasmid)

Answer: (D)

Conjugation is a method of gene transfer that requires direct contact between bacterial cells. The key feature is that DNA is passed from a donor to a recipient through a mating bridge formed by the fertility factor, the F plasmid. An F+ donor cell uses a sex pilus to connect with an F− cell and transfers the plasmid DNA, usually as a single-stranded molecule that the recipient copies to become double-stranded. This process can make the recipient an F+ donor as well, spreading the plasmid through a population; occasionally, chromosomal genes can be transferred if the F factor is integrated into the chromosome (creating an Hfr cell). This direct, contact-dependent transfer of plasmid DNA is what sets conjugation apart from other DNA uptake methods like transformation, which involves picking up naked DNA from the environment, and transduction, which is DNA transfer mediated by a bacteriophage.