Practice question

Conjugation requires physical cell-to-cell contact established by sex pilus encoded by tra operon of conjugative plasmid. Donor F+ extends pilus, attaches to recipient F- surface receptor, retracts to bring cells close, and forms conjugative junction or mating bridge. Type IV secretion system then transfers single-stranded plasmid DNA in 5' to 3' direction, with rolling circle replication replacing donor strand. Chemical or enzymatic treatment that prevents pairing abolishes transfer. Experimental interrupted mating exploits contact dependence to map gene order by timing of marker entry into recipient.