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Questions and Answers
What is transformation in bacteria?
What is transformation in bacteria?
- Modification of a cell by the uptake of extracellular DNA (correct)
- The process of transferring genetic material via a plasmid
- A technique to introduce DNA using electrical pulses
- Modification of a cell by direct transfer of DNA
What does conjugation involve in bacteria?
What does conjugation involve in bacteria?
- Incorporation of extracellular DNA
- Direct transfer of DNA between two cells (correct)
- Creation of hybrid DNA molecules
- Mapping distance between genes
What does the term 'donor' refer to in bacterial conjugation?
What does the term 'donor' refer to in bacterial conjugation?
A plasmid called F factor, transferred to recipient
What are Hfr strains known for?
What are Hfr strains known for?
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What is transduction in bacteria?
What is transduction in bacteria?
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Define auxotrophs.
Define auxotrophs.
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What does 'Replica plating' refer to?
What does 'Replica plating' refer to?
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What does competent cells mean?
What does competent cells mean?
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Two genes must be close together if the frequency of cotransformation is higher than expected.
Two genes must be close together if the frequency of cotransformation is higher than expected.
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Who discovered the F factor?
Who discovered the F factor?
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Define transconjugants.
Define transconjugants.
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Study Notes
Transformation
- Involves uptake and incorporation of extracellular DNA by bacterial cells, leading to genetic modification.
Conjugation
- Direct DNA transfer between two bacteria through temporary cell connection.
- Requires a donor cell with an F factor plasmid, which gets transferred to the recipient.
Hfr Strains
- High frequency recombination results from integration of the F factor into a bacterial chromosome.
Transduction
- Genetic material transfer between bacteria mediated by a plasmid or bacteriophage.
Mapping Techniques
- Intergenic Mapping: Measures distance between mutations in different genes.
- Intragenic Mapping: Measures distance between mutations within the same gene.
Cis-Trans Test
- Determines whether mutations in viral genes complement each other based on their gene location; mutations in different genes complement, while mutations in the same gene do not.
Auxotrophs vs. Prototrophs
- Auxotrophs: Mutants unable to synthesize essential nutrients, requiring them from media.
- Prototrophs: Capable of synthesizing all necessary nutritional requirements.
Mutation Notation
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- superscript indicates wild type capable of synthesis; absence indicates mutant unable to synthesize.
Replica Plating
- Technique for isolating auxotrophs by transferring bacterial colonies onto selective media, allowing differentiation between prototrophs and auxotrophs.
Transformants
- Recombinant bacterial cells that exhibit altered phenotypes after transformation.
Electroporation
- Method introducing DNA into cells by applying an electrical pulse, creating pores in cell membranes for DNA entry.
Competent Cells
- Bacteria that can naturally uptake and integrate external DNA.
Transformation Types
- Natural Transformation: Uptake of free DNA naturally occurring in species like Bacillus subtilis.
- Engineered Transformation: Bacteria, such as E. coli, are modified to enhance DNA uptake capabilities.
Heteroduplex DNA
- Hybrid DNA formed from complementary strands of similar, but not identical, DNA molecules.
Gene Linkage
- Two genes are considered closely related if cotransformation frequencies are higher than expected based on individual transformation rates, indicating they are often inherited together.
Transconjugants
- Bacteria that successfully receive DNA from a donor during conjugation.
Key Discoveries
- Conjugation was established by Lederberg and Tatum.
- F factor discovery credited to William Hayes.
F pili/Sex pili
- Specialized structures that facilitate DNA transfer between bacteria, encoded by the F plasmid.
Conjugation Limitations
- No conjugation occurs between cells of the same mating type (F+ with F+ or F- with F-).
Effects of Continued Conjugation
- Results in increased proportion of F+ cells in the bacterial population over time.
Curing
- Chemical exposure that hinders the replication of the F factor.
Genetic Transfer in F+ F- Crosses
- Transfers only the F factor and not the bacterial chromosome during F+ and F- cell interactions.
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