Bacterial Genetics Chapter 7

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.

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!