Chapter 9 exam 3 Flashcards
(23 cards)
What is horizontal gene transfer, and how does it differ from vertical gene transfer?
Horizontal gene transfer (HGT) is the transfer of genetic material between organisms in a manner other than traditional reproduction.
In contrast, vertical gene transfer refers to the transmission of DNA from parent to offspring during reproduction.
How is it possible for two organisms within the same genus and species to have genomes that differ in size and gene number?
They differ because of horizontal gene transfer. O157:H7 has acquired genomic islands including virulence factors, such as toxin genes and adhesion factors, that make it pathogenic. K12 lacks these, which is why it is safe for lab use.
What is a genomic island?
A genomic island is a large DNA segment in a genome that has been acquired through horizontal gene transfer (non-traditional reproduction)
What are some examples of genomic islands?
Examples include pathogenicity islands, symbiosis islands, metabolic islands, and antibiotic resistance islands.
How can relative GC content, codon usage, amino acid usage, and gene arrangement identify horizontally transferred genome portions?
HGT-acquired DNA often has different GC content than the host genome, unusual codon bias or rare codons, distinct amino acid usage patterns, and disrupted or irregular gene arrangement.
What is transformation?
Transformation is the uptake and incorporation of free DNA from the environment into a bacterial cell.
What does it mean for a cell to be (or become) competent?
A competent cell is capable of taking up extracellular DNA. Some bacteria are naturally competent, while others become competent under specific conditions (e.g., starvation).
What is a transformasome?
A transformasome is a membrane-bound protein complex in Gram-positive bacteria that captures and transports DNA into the cell.
What role do competence factors play in the synthesis of transformasomes?
Competence factors (CFs) trigger the formation of transformasomes through quorum sensing.
Why do bacteria wait until there are a certain number of organisms around before synthesizing transformasomes?
Bacteria use quorum sensing to assess population density. Synthesizing transformasomes is energetically costly, so they wait until the community is large enough to increase the chance of acquiring useful DNA.
What are the benefits of transformation?
Benefits include nutrients (DNA as food), DNA repair, and acquisition of new traits (e.g., antibiotic resistance, new metabolic capabilities).
What is conjugation?
Conjugation is the transfer of DNA via direct cell-to-cell contact.
What is the difference between an F+ cell and an F- cell?
F+ cell contains the Fertility (F) plasmid, while F- cell does not.
What happens to the F- cell after successful conjugation?
After conjugation, the F- cell becomes F+.
Why is it beneficial for the donor strain to donate only 1 strand of the plasmid?
Donating a single strand allows the donor to retain its own copy and speeds up replication of the transferred plasmid in the recipient.
What is a conjugation pilus?
The F+ cell forms a conjugation pilus, which connects it to the F- cell.
How does the single strand of DNA move from one organism to the other during conjugation?
The plasmid is nicked, and a single DNA strand is transferred through the pilus, then replicated in the recipient.
What is a high-frequency recombination strain?
An Hfr strain is a bacterium in which the F plasmid has integrated into the chromosome, allowing it to transfer chromosomal genes along with the plasmid DNA during conjugation.
What is transduction?
Transduction is DNA transfer via bacteriophages.
What is the difference between generalized and specialized transduction?
Generalized transduction transfers random host DNA, while specialized transduction transfers only specific, adjacent genes.
How does the capability of lysogeny affect transduction?
Lysogenic phages can perform specialized transduction, while lytic phages can only do generalized transduction.
How is horizontal gene transfer (HGT) impacted in the human gut?
HGT occurs through transformation, conjugation, and transduction. Antibiotics create stress and selective pressure, promoting conjugation and transformation, especially of resistance genes.
Which type of HGT might result in the spread of antibiotic resistance?
All three types can, but conjugation is the most common and efficient route for spreading antibiotic resistance genes, especially through plasmids.
