Untitled Quiz

Bacterial Genetics

• Bacterial genetics studies inheritance and variation in bacteria.
• All inherited traits are encoded in DNA.
• Bacterial nucleic acids include DNA (chromosome and plasmids) and RNA (tRNA, rRNA, mRNA).

Bacterial Chromosome

• A bacterial chromosome is a single, supercoiled, circular double-stranded DNA helix.
• Genetic information is stored as a sequence of bases in this molecule.

Gene

• A gene is a unit of heredity.
• A gene is a DNA segment carrying information for a specific biochemical or physiological property.
• Genes are carried on the bacterial chromosome.
• Genes are essential for bacterial growth.

Plasmids

• Definition: Extrachromosomal, small circular, double-stranded helical DNA.
• Properties: Do not code for essential bacterial functions for survival. Separate replicon or episome.
• Functions:
  • Antibiotic resistance (R factor).
  • Toxin production.
  • Bacteriocins (toxic proteins killing other bacteria).
  • Some surface antigens

Variation

• Observable change in a species.
  • Phenotypic variation: Genes are not modified; expression is altered in response to the environment (e.g., sporulation).
  • Genotypic variation: Genetic alteration, heritable.
    • Mutation: Alteration of the nucleotide sequence of an organism's DNA. Spontaneous or induced by physical or chemical agents (e.g., heat, radiation, chemicals). Heritable. Types include base substitution, frameshift, insertion, and deletion.
    • Genetic Transfer: Transfer between cells (e.g., transformation, transduction, conjugation) or within same cell (e.g., transposition).

Transposition

• Transposable elements (transposons or "jumping genes") move from one DNA site to another in the genome.
• Transposons insert into DNA at random positions. 

Transformation

• DNA release from dead cells (lysis) followed by uptake by recipient cells. Recipient cells need to be competent.
• Any gene can be transformed.

Transduction

• Bacteriophages (bacteria viruses) act as vectors transferring DNA from donor to recipient bacteria.

Conjugation

• Plasmid-mediated mating (joining) of two bacteria.
• DNA transfer from a donor to a recipient through direct cell contact and sex pilus formation.
• The mating process is controlled by an F (fertility) plasmid, which carries genes for proteins required for mating (e.g., sex pilin).
• The process involves the transfer of one strand of the F plasmid. Recipient cell replication results in an F+ cell.
• During mating, the pilus of the donor F+ bacterium attaches to the recipient F- bacterium.
• F-Plasmid DNA is enzymatically cleaved and transferred across the bridge into the recipient cell.
• The process completes with strand synthesis forming a double-stranded F plasmid in both cells.
• The recipient cell now can transmit the plasmid.

Recombination

• Successful gene transfer requires recombination, which inserts the transferred genetic element into the recipient's DNA, ensuring inheritance in progeny.

Abortive Transfer

• Otherwise, the transferred DNA remains a short time before being diluted out.