The Molecular Genetics of Bacteria

Rucete ✏ Biology In a Nutshell

1. Bacterial Genome

• Bacteria have a single, circular DNA molecule that functions as their main chromosome.
• This DNA contains most of the genetic information necessary for the cell's structure and function.

2. Plasmids

• Plasmids are small, circular, double-stranded DNA molecules separate from the chromosomal DNA.
• They can carry genes that confer advantages, such as antibiotic resistance.

3. Episomes

• Episomes are a type of plasmid that can integrate into the bacterial chromosome.
• They can exist either independently or as part of the chromosome.

4. Genetic Variation in Bacteria

Bacteria can exchange genetic material through three main mechanisms:

a) Conjugation

• A donor bacterium transfers DNA to a recipient bacterium through a structure called a pilus.
• The donor may transfer plasmid DNA or even parts of its chromosomal DNA.
• F plasmid: allows the formation of the pilus and transfer of plasmid DNA.
• R plasmid: carries genes that provide antibiotic resistance.

b) Transduction

• Involves a virus (bacteriophage) transferring DNA from one bacterium to another.
• During the lytic cycle, the virus may accidentally package bacterial DNA instead of viral DNA and transfer it to a new host cell.

c) Transformation

• A bacterium takes up DNA fragments from its surroundings (environment) and integrates them into its own genome.