Questions and Answers
What is horizontal gene transfer and what is the difference between horizontal and vertical gene transfer?
Horizontal gene transfer is the transfer of genes between members of the same generation, while vertical gene transfer is the transfer of genes from one generation to the next.
In the Fred Griffith experiment, identify the bacteria he used and the outcome of his experiment.
He used two strains of Streptococcus pneumoniae: the capsulated (S) strain and the non-capsulated (R) strain. The outcome showed that the live S strain killed the mouse, while the R strain did not.
How can cells be artificially transformed?
Cells can be artificially transformed through methods like electroporation or chemical transformation using CaCl2 and heat shock.
What is the role of pili in conjugation?
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What is the difference between conjugation and transformation?
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Identify which horizontal transfer process involves DNA pieces being transferred by cells.
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What codes for the origin of transfer?
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Is the R plasmid self or non-self transmissible?
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What are the two different processes of transduction mediated by bacteriophages?
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Study Notes
Horizontal Gene Transfer
- Horizontal gene transfer involves the transfer of genetic material between organisms of the same generation, common in bacteria.
- Accomplished through three processes: transformation, transduction, and conjugation.
- In contrast, vertical gene transfer involves passing genetic information from one generation to the next.
- Requires a donor cell (transmitter) and a recipient cell (acceptor), with DNA integrated into the recipient's genome.
- Incorporates only single-stranded regions, even if double-stranded DNA is present, and is typically rare but significant for evolution.
Fred Griffith Experiment
- Used two strains of Streptococcus pneumoniae, capsulated (S) and non-capsulated (R).
- S strain is pathogenic and can evade immune responses, whereas R strain is non-pathogenic.
- Observations:
- Live S strain → mouse dies
- Dead S strain → mouse lives
- Live R strain → mouse lives
- Live R + Dead S → mouse dies, with live S recovered from the culture.
- Demonstrated that DNA is the genetic material responsible for transformation.
Artificial Transformation
- Competence can be artificially induced in bacteria, like Escherichia coli, using temperature and salt manipulation.
- Electroporation technique uses high voltage to open pores in cell membranes, allowing DNA uptake.
- Chemical transformation employs calcium chloride and heat shock to facilitate DNA entry, reducing electrostatic repulsion and promoting binding.
Role of Pili in Conjugation
- Pili mediate the transfer of DNA between adjacent bacteria; plasmids or entire genomes may be transferred.
- Involves F+ (donor) and F- (recipient) cells, with F plasmid encoding for sex pili.
- Process:
- F pili binds to an F- cell, drawing the two cells close.
- Plasmid is cut, and one strand transfers to the recipient.
- Recipient synthesizes a complementary strand, converting to F+ while the donor restores its plasmid.
Conjugation vs. Transformation
- Conjugation necessitates physical contact between donor and recipient cells; transformation does not.
- Conjugation requires cells of opposite mating types, unlike transformation, which involves naked DNA uptake.
- Larger quantities of DNA are transferred during conjugation, which is always unidirectional from F+ to F-.
Transformation Process
- Transformation is specifically the horizontal gene transfer process where recipient cells uptake DNA fragments from the environment.
Origin of Transfer
- The F plasmid encodes the origin of transfer necessary for plasmid transfer during conjugation.
R Plasmids and Conjugation
- R plasmids confer resistance to antimicrobial agents and are self-transmissible, encoding the origin of transfer and sex pili for conjugation.
- Composed of resistance genes and resistance transfer factors, allowing horizontal gene transfer across various bacterial species.
Transduction Process
- Transduction involves bacteriophages transferring DNA between bacteria in two types: generalized and specialized transduction.
- Phages inject their DNA into bacterial cells, degrading host DNA and incorporating some into new phages.
- Transducing phages can inadvertently carry and inject bacterial DNA into recipient cells.
- Generalized transduction transfers random DNA fragments, while specialized transduction transfers specific sequences, often including virulence factors responsible for diseases like diphtheria and scarlet fever.
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Description
Explore key concepts in bacterial genetics, focusing on horizontal and vertical gene transfer. This quiz will help you understand how genetic material is shared among bacteria and its implications in evolution and adaptation. Test your knowledge with these flashcards!
