Genetics of Prokaryotes (2B) - MCAT Biological and Biochemical Foundations of Living Systems

Small circular extrachromosomal dsDNA that replicates independently. Plasmids provide genetic flexibility in prokaryotes by carrying accessory genes that can be horizontally transferred and replicated separately from the chromosome.

Conjugative plasmid. These plasmids encode transfer genes enabling self-propagation through conjugation between bacterial cells.

Genes for sex pilus formation and DNA transfer (tra genes). These genes facilitate the formation of a conjugation bridge and single-stranded DNA transfer during bacterial mating.

F+ contains the F plasmid; F− lacks the F plasmid. The presence of the F plasmid determines the donor capability in conjugation, distinguishing between donor and recipient cells.

Donor remains F+; recipient becomes F+. During conjugation, a copy of the F plasmid is transferred, allowing both cells to potentially act as donors afterward.

Cell with F factor integrated into the bacterial chromosome. Integration of the F plasmid into the chromosome allows transfer of chromosomal genes during conjugation.

High frequency of recombination. This acronym reflects the enhanced rate of genetic recombination due to efficient chromosomal DNA transfer in conjugation.

Chromosomal DNA adjacent to the integrated F origin of transfer. The origin of transfer site directs the sequential mobilization of DNA starting from the integrated F factor's position.

F− (transfer usually stops before the entire F factor enters). Conjugation bridges often break before the full F factor transfers, preventing the recipient from gaining donor capability.

F plasmid that excised with adjacent chromosomal genes. Imprecise excision incorporates host DNA into the plasmid, enabling transfer of specific chromosomal genes via conjugation.

Conjugation. This process requires a sex pilus for cell contact and involves rolling-circle replication to transfer single-stranded DNA.

Uptake of naked DNA from the environment by a bacterium. Competent bacteria can incorporate environmental DNA into their genome, facilitating genetic variation without cell contact.

Able to take up exogenous DNA (naturally or artificially induced). Competence involves specific physiological states or treatments that enable DNA binding and uptake across the cell membrane.

Transfer of bacterial DNA mediated by a bacteriophage. Bacteriophages package and deliver bacterial DNA during infection, enabling gene transfer between hosts.

Generalized: any gene; specialized: only genes near prophage site. Generalized involves random DNA packaging during lytic cycle, while specialized requires prophage excision carrying adjacent genes.

Transposition. This mechanism allows mobile genetic elements to relocate, contributing to genome evolution and antibiotic resistance spread.

Transposase. Transposase recognizes inverted repeats and catalyzes cut-and-paste or replicative movement of the transposon.

Plasmid carrying antibiotic resistance genes. These plasmids confer survival advantages in antibiotic environments by encoding resistance mechanisms like efflux pumps.

Rapid horizontal spread of antibiotic resistance between bacteria. Conjugation allows quick dissemination of resistance genes across bacterial populations, complicating infection treatments.

Gene transfer between organisms not via parent-to-offspring inheritance. HGT enables rapid adaptation by acquiring genes from unrelated organisms through mechanisms like conjugation or transformation.

Transduction. Bacteriophages act as vectors in transduction, unlike the direct contact in conjugation or DNA uptake in transformation.

Transformation. This mechanism relies on competent cells absorbing extracellular DNA released from lysed bacteria in the environment.

Hfr cell. Integration of F into the chromosome enables high-efficiency transfer of linked bacterial genes during conjugation.

F′ (F prime). Aberrant excision merges plasmid and chromosomal DNA, creating a hybrid capable of specialized gene transfer.