CHAPTER 7 Flashcards
(40 cards)
How do allelic differences affect bacterial traits?
Bacteria, often haploid, affect traits like antibiotic sensitivity and nutrient requirements.
How do bacteria reproduce, and how is genetic diversity achieved?
-Bacteria reproduction: Asexually
-Genetic Diversity: genetic Transfer
What is genetic transfer in bacteria, and why is it important?
-Genetic transfer: allows bacteria to share genetic material
-Importance: enhances genetic diversity
Three mechanisms of genetic transfer in bacteria
- Conjugation
- Transduction
- Transformation
Conjugation
Direct contact between cells
Transduction
DNA transfer via bacteriophages
Transformation
DNA uptake from the environment
Bacterial conjugation
process where direct contact between a donor and recipient cell allows DNA transfer, often involving plasmids.
How does transduction work in bacteria?
Bacteriophages transfer DNA from a donor cell to a recipient, where it integrates into the recipient’s chromosome.
Who discovered genetic transfer in bacteria?
Joshua Lederberg and Edward Tatum with E. coli
Auxotrophs
Requires specific nutrients in the medium
Prototrophs
Can synthesize all required nutrients
What was the outcome of Lederberg and Tatum’s experiment?
Mixing strains allowed some cells to acquire genes to grow on a minimal medium, indicating genetic transfer.
Conjugation definition in bacteria
Conjugation refers to transferring DNA from one bacterium to another through direct cell-to-cell contact.
What are F factors in bacteria?
F factors (fertility factors) are small circular pieces of DNA that carry genes required for conjugation, found in certain donor strains of E. coli.
How are bacterial strains categorized based on F factors?
-F+: Strains containing the F factors
-F-: Strains not containing the F factor
Role of sex pili (F pili) in bacterial conjugation?
-Produced by F⁺ strains
-Facilitate the attachment of F⁻ bacteria
-Initiate the conjugation process
What happens during the contact phase of conjugation?
-Sex pili shorten
-Brings donor and recipient cells closer together
-Form a conjugation bridge
Mechanism of DNA transfer during conjugation.
- A relaxosome recognizes the origin of the transfer and cuts the DNA.
- Relaxase binds to the cut DNA (T-DNA) while the exporter pumps DNA into the recipient cell.
- The F factor is replicated, and the recipient cell becomes F⁺.
Plasmids
Extra-chromosomal DNA molecules that can replicate independently of the bacterial chromosome and may provide growth advantages.
5 plasmids categories
- Fertility plasmids: Allow conjugation.
- Resistance plasmids (R factors): Provide antibiotic resistance.
- Degradative plasmids: Enable digestion of unusual substances.
- Col-plasmids: Encode colicins that kill other bacteria.
- Virulence plasmids: Turn bacteria into pathogenic strains.
What happens when an F⁺ cell conjugates with an F⁻ cell?
Both cells become F⁺ after conjugation, as the F factor is transferred to the F⁻ cell.
What is an Hfr strain, and how does it relate to conjugation?
-Hfr (high frequency of recombination) strains are derived from F⁺ strains
-efficient at transferring chromosomal genes during conjugation
How can F factors be excised from the bacterial chromosome?
Integrated F factors can be excised imprecisely, resulting in F’ factors that carry additional chromosomal genes.
