Molecular Genetics: Microbial Genetics, Chromosome Organization, DNA Replication, and Transcription

Conjugation

A mechanism of bacterial genetic exchange involving the direct, unidirectional transfer of genetic material from a donor cell to a recipient cell through physical contact via a conjugation bridge or sex pilus.

Transformation

The mechanism of bacterial genetic exchange in which a competent bacterial cell takes up naked, extracellular DNA fragments directly from the surrounding medium and incorporates them into its genome.

Transduction

The transfer of bacterial genes from one bacterial host cell to another mediated by an infectious bacteriophage vector.

Fertility (F) Factor

A specialized circular episome/plasmid in bacteria that encodes genes for plasmid replication ($rep$, $inc$), integration sequences ($IS2$, $IS3$), and proteins necessary for sex pilus assembly and transfer across the origin of transfer ($oriT$).

Hfr (High Frequency Recombination) Strain

A bacterial strain in which the F factor plasmid has integrated into the circular bacterial chromosome by crossing over, allowing chromosomal genes to be transferred linearly behind the origin of transfer to an $F^-$ recipient cell during conjugation.

Interrupted Mating Technique

A classical bacterial genetic mapping method in which conjugation between an Hfr donor and an $F^-$ recipient is mechanically disrupted at specific time intervals to determine gene order and genetic distance measured in minutes.

Competence

The transient physiological state of a bacterial cell that confers an increased ability to bind and internalize extracellular DNA across the cell membrane.

R Plasmid

A bacterial resistance plasmid consisting of a resistance transfer factor (RTF) segment responsible for transfer and an r-determinant region carrying genes conferring resistance to multiple antibiotics and toxins.

T4 Phage

A virulent double-stranded DNA bacteriophage that infects $Escherichia\text{ }coli$, structurally organized into an icosahedral head packaging DNA, a collar, a contractile tail sheath tube, a base plate, and tail fibers.

Lytic Cycle

A viral reproductive cycle where phage DNA takes over host replication machinery, directs the degradation of the host chromosome, produces mature viral progeny, and lyses the host cell to release virions.

Lysogenic Cycle

A temperate phage cycle where phage DNA integrates into the host bacterial chromosome as a prophage and passively replicates along with the host chromosome without lysing the cell.

Retrovirus

An RNA animal virus that utilizes viral reverse transcriptase to synthesize complementary DNA from its RNA genome and viral integrase to insert this DNA into the host genome to form a permanent provirus.

Nucleoid