Bacterial Chromosome and Plasmids

Bacterial Chromosome

• The bacterial chromosome is a circular, double-stranded DNA molecule attached to the bacterial cell membrane.

DNA Replication in Bacteria

• DNA replication in bacteria is semi-conservative, meaning each original DNA strand is conserved intact during replication and becomes one of the two strands of the new daughter molecules.

Plasmids

• Plasmids are self-replicating, extra-chromosomal DNA molecules that multiply independently of the host cell.
• Multiple copies of the same plasmid can be present in each bacterial cell.
• Different plasmids can also be present in the same bacterial cell.

Types of Plasmids

• R factors: Plasmids that contain genes coding for antibiotic resistance.
• Col factors: Plasmids that contain genes coding for extracellular toxin (colicines) production, which inhibit strains of the same and different species of bacteria.
• F (fertility) factors: Plasmids that can recombine with the bacterial chromosome, promoting the transfer of the chromosome at a high frequency of recombination into the chromosome of a second (recipient) bacterial cell during mating.