Gene Transfer Mechanisms Flashcards
What is Gene transfer?
The transfer of DNA from one cell (donor cell) to another (recipient cell)
What are the three ways of gene transfer?
- conjugation
- transduction
- transformation
What is the significance of gene transfer?
- antibiotic resistance
- virulence/ pathogenicity
- new strains/ emerging infections
what structures or processes contribute to drug resistance?
plasmids, transposons, enzyme (lactase) and gene transfer
Describe the process of transformation
Transformation is the direct uptake of naked DNA/ fragmented DNA. It occurs when one bacterium lyses and releases its genetic content, while another bacterium comes and acquires it.
Transformation was proved in 1928 by Frederick Griffith when he experimented on streptococcus pneumoniae.
- when S- bacteria was injected, the mice died
- when R- bacteria was injected, the mice lived
- when heat killed S- bacteria was injected, the mice lived
- when S- bacteria and heat killed R-bacteria was injected, the mice died
- when heat killed S- bacteria and R-bacteria and deoxyribonuclease was injected, the mice survived
IF DNA IS PRESENT, ORGANISM WILL DIE
Describe the process of transduction
Transduction is the transfer of genetic material from one bacterium to another by a bacteriophage.
There are two ways:
- generalized transduction
- specialized transduction
In generalized transduction:
- the bacteriophage injects its DNA into the donor cell.
- the phage enzymes degrade host DNA
- cell synthesizes new phases that incorporate phage DNA and mistakenly, some host DNA
- the transducing phage (phage with donor DNA) injects the donor DNA into the recipient cell
- the donor DNA is incorporated into the recipient’s chromosome by recombination
what are the structures of the bacteriophage?
- head/capsid (made up of nucleic acid and protein)
- tail and contractile sheath
- tail fibers
- base
what are the two existing phases of bacteriophages?
- virulent (lytic) phase: where the bacteriophages kill the host cell immediately
- lysogenic phase: where the bacteriophages do not kill the host immediately and integrates into the chromosome
describe the process of conjugation
Conjugation is the transfer of genetic material from a donor cell to a recipient cell by direct cell-cell contact.
In gram negative bacteria, the gene (plasmid) is transferred using sex pilus.
F+ x F-:
The donor cell is F+ (contains fertility factor and plasmid which gives it the ability to make sex pilus) and the recipient cell is F- (plasmid deficient)
1. donor cell attaches to recipient cell and is drawn together via sex pilus (conjugation tube)
2. one strand of plasmid DNA from F+ cell (donor) transfers to the F- cell (recipient)
3. recipient synthesizes a complementary strand to become a F+ cell and donor synthesizes a compkentary strand to restore its complete plasmid
End Result of F+ x F- is both participants are F+
Hfr x F-:
the donor cell is Hfr (high frequency recombination-cell with plasmid integrated into the chromosome) and the recipient cell is F-
1. donor cell and recipient cell are attched by sex pilus
2. donor DNA is replicated by rolling-circle method and transferred to recipient cell
3. fragment of donor DNA is incorporated into recipient chromosome
End result of Hfr x F- is the F- recipient does not become F+ unless the WHOLE chromosome is transferred
what is the F’ cell?
deintegration of plasmid with chromosomal DNA from Hfr cell
what is the most common method of gene transfer?
conjugation
what is the most common method of conjugation?
Hfr x F-
how to identify the conjugation process?
genes transferred between 2 living cells, pili is present and plasmids are transferred
how to identify the transformation process?
a dead cell (donor), streptococcus (s+r), deoxyribonuclease, antibiotic/host defense molecule (lysozyme/ heat)
how to identify the transduction process?
bacteriophage, toxin gene transfer
