Genetics of Prokaryotes (2B) - Bio & Biochem
- What is the usual outcome for donor and recipient after F+ × F− conjugation?
- 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.
- Choose the expected recipient outcome: an F+ donor mates with an F− recipient and transfer completes.
- Recipient becomes F+. Complete transfer of the F plasmid copy converts the recipient to a donor, promoting plasmid spread in the population.
- Which DNA is transferred first during Hfr 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.
- What is the major clinical significance of conjugative R plasmids?
- Rapid horizontal spread of antibiotic resistance between bacteria. Conjugation allows quick dissemination of resistance genes across bacterial populations, complicating infection treatments.
- Which option best defines bacterial transformation?
- 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.
- Which option describes an F+ cell compared with an F− cell?
- 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.
- Which process requires a bacteriophage: transformation, conjugation, or transduction?
- Transduction. Bacteriophages act as vectors in transduction, unlike the direct contact in conjugation or DNA uptake in transformation.
- What is the key distinction between generalized and specialized transduction?
- 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.
- Which option best defines an R plasmid in bacteria?
- Plasmid carrying antibiotic resistance genes. These plasmids confer survival advantages in antibiotic environments by encoding resistance mechanisms like efflux pumps.
- What does Hfr stand for?
- High frequency of recombination. This acronym reflects the enhanced rate of genetic recombination due to efficient chromosomal DNA transfer in conjugation.
- What does it mean for a bacterium to be competent?
- 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.
- What is horizontal gene transfer (HGT) in prokaryotes?
- 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.
- What is the term for movement of a DNA segment within a genome or between DNA molecules?
- Transposition. This mechanism allows mobile genetic elements to relocate, contributing to genome evolution and antibiotic resistance spread.
- Identify the transfer mechanism: uptake of free DNA by a competent bacterium.
- Transformation. This mechanism relies on competent cells absorbing extracellular DNA released from lysed bacteria in the environment.
- Identify the donor type: F factor integrated into chromosome and transfers chromosomal genes at high frequency.
- Hfr cell. Integration of F into the chromosome enables high-efficiency transfer of linked bacterial genes during conjugation.
- Which option best defines bacterial transduction?
- Transfer of bacterial DNA mediated by a bacteriophage. Bacteriophages package and deliver bacterial DNA during infection, enabling gene transfer between hosts.
- What is an Hfr cell in bacterial conjugation?
- Cell with F factor integrated into the bacterial chromosome. Integration of the F plasmid into the chromosome allows transfer of chromosomal genes during conjugation.
- What does the F factor encode that enables conjugation?
- 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.
- What is an F′ (F prime) plasmid?
- F plasmid that excised with adjacent chromosomal genes. Imprecise excision incorporates host DNA into the plasmid, enabling transfer of specific chromosomal genes via conjugation.
- What enzyme catalyzes movement of a transposon?
- Transposase. Transposase recognizes inverted repeats and catalyzes cut-and-paste or replicative movement of the transposon.
- What is the term for a plasmid that can transfer itself between bacteria?
- Conjugative plasmid. These plasmids encode transfer genes enabling self-propagation through conjugation between bacterial cells.
- What is the most common F status of the recipient after Hfr × F− conjugation?
- 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.
- Which option best defines a plasmid in prokaryotes?
- 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.
- Which F status is produced when an F plasmid excises incorrectly and carries a host gene into the plasmid?
- F′ (F prime). Aberrant excision merges plasmid and chromosomal DNA, creating a hybrid capable of specialized gene transfer.
- What is the term for transfer of bacterial DNA via direct cell-to-cell contact?
- Conjugation. This process requires a sex pilus for cell contact and involves rolling-circle replication to transfer single-stranded DNA.