Horizontal Gene Transfer Flashcards
Fill in the blanks:
While sexual reproduction is _________ to produce offsprings, asexual reproduction generates offsprings more ________.
Slower; Quickly
*in sexual 2 gametes need to come together, whereas in asexual chromosome replicates and there’s cell division.
(T/F) Both sexual and asexual reproduction generate equal amount of diversity.
False! Sexual reproduction generates more diversity than asexual reproduction.
How does sexual reproduction generate diversity?
1) Material from 2 parents
2) Crossover
3) Independent assortment of chromosomes during meiosis
4) Chromosomal segregation not always correct
*lots of room 4 evolution
Why does asexual reproduction generate less diversity?
1) Identical genome passed down to daughter cells
2) Mutations (that give rise to selective advantage) are random n rare
(T/F) While sexual reproduction is vertical transmission of genetic material, asexual reproduction is horizontal transmission.
False! They are both vertical transmission.
What is the difference between horizontal gene transfer and vertical gene transfer?
Horizontal gene transfer is between closely or sometimes distantly related species (only small pieces of DNA at a time), whereas vertical gene transfer is between mother n daughter cells.
Match the following types of horizontal gene transfer with their description:
1) Transformation
2) Transduction
3) Conjugation
A) Genes are transferred between cells by a virus. Can be specialized or generalized.
B) Direct exchange of DNA material by 2 cells; Donor and Recipient. Can be done through pili, Type 4 secretion system (T4SS) or nanotubes.
C) Absorption of naked eDNA or eDNA within vesicles by the cell
1) Transformation: Absorption of naked eDNA or eDNA within vesicles by the cell
2) Transduction: Genes are transferred between cells by a virus. Can be specialized or generalized.
3) Conjugation: Direct exchange of DNA material by 2 cells; Donor and Recipient. Can be done through pili, Type 4 secretion system (T4SS) or nanotubes.
*horizontal gene transfer occurs to introduce diversity !
(T/F) Because many bacteria are naturally competent for transformation, transformation is often used in molecular biology to introduce new genetic material into a new organism.
True!
Match the following steps of transformation:
1) Step 1
2) Step 2
3) Step 3
4) Step 4
A) ssDNA is bound by specific proteins and there is a recombination with homologous regions of the bacterial chromosome mediated by RecA protein.
B) Binding of dsDNA by membrane-bound DNA binding protein.
C) The cell is now transformed.
D) Uptake of one of the 2 strands into the cell while nuclease activity degrades the other strand.
Step 1: Binding of dsDNA by membrane-bound DNA binding protein.
Step 2: Uptake of one of the 2 strands into the cell while nuclease activity degrades the other strand.
Step 3: ssDNA is bound by specific proteins and there is a recombination with homologous regions of the bacterial chromosome mediated by RecA protein.
Step 4: The cell is now transformed.
What is recombinant DNA?
DNA that is added to the wildtype genome during transformation.
(T/F) The exo/endonucleases that digest one of the strands of the dsDNA in the cytoplasm for transformation are also highly effective against the ssDNA.
False! The exo/endonucleases that digest one of the strands of the dsDNA in the cytoplasm are highly INEFFECTIVE against the ssDNA.
*the digested strand becomes free nucleotides that is available as food for the cells.
What is the difference between natural and artificial competence?
Natural competence: Regulated in bacteria. An example is quorum sensing regulating competence.
Artificial competence: An example of it is genetically engineered lab strains of E.Coli to be chemically/heat induced.
(T/F) In transformation, whatever was coded on the recombinant DNA becomes an integral part of the bacterial genome and can change the phenotype (new toxin, enzyme, proteins).
True!
Why is transformation not very efficient at introducing diversity?
1) Relatively little environmental DNA; rarely a whole coding piece
2) Recombination requires the DNA to be similar to the genomic DNA for a length of nucleotides
3) Nucleases can digest the ssDNA fragments, even though they are less efficient.
Though transformation is not very efficient at introducing diversity, what is it still important for?
To acquire tolerance to antibiotics or virulence.
How does V. cholerae become pathogenic?
Horizontal gene transfer by SPECIALIZED TRANSDUCTION
Answer the questions regarding cholera:
1) What kind of bacteria causes cholera?
2) What are the symptoms of cholera?
3) What causes the symptoms of cholera? How?
1) Gram-negative curved rod (Vibrio Cholerae)
2) Diarrhea + dehydration
3) Production of CHOLERA TOXIN (CT). CT activates a chloride transporter to pump chloride ions out of the epithelial cells into the gut lumen. Water follows the chloride ions, causing diarrhea + dehydration.
How does Vibrio Cholerae acquire the gene encoding the cholera toxin (CT)?
Through infection with the lysogenic filamentous CTX PHAGE.
The phage carries the CT gene and introduces it into the chromosome on integration of the prophage.
What is phage conversion?
Alteration of the phenotype of a host cell by LYSOGENIZATION (integration of phage DNA into host chromosome)
(T/F) Prophage from normal, non-defective temperate (viral replication along with host DNA) infection can be reinfected by same phage or phages of same type.
False!
Prophage from normal, non-defective temperate (viral replication along with host DNA) infection become immune to further infection by same phage or phages of same type
Not sure why; maybe an evolutionary advantage?
(T/F) For cholera, transduced cells may acquire new phenotypic abilities such as virulence, if enough DNA material encoding for virulence factors was exchanged.
True!
Match the following bacteria and the phage it is infected by to what virulence it leads to.
1) Salmonella enterica & bacteriophage e15
2) Corynebacterium diphtheriae & bacteriophage β
A) Conversion of non-pathogenic bacteria to pathogenic; toxin is being produced.
B) Change in polysaccharide produced at the surface level.
Salmonella enterica & bacteriophage e15: Change in polysaccharide produced at the surface level.
Corynebacterium diphtheriae & bacteriophage β: Conversion of non-pathogenic bacteria to pathogenic; toxin is being produced.
Match the following terms to their definition regarding transduction:
1) Generalized transduction
2) Specialized transduction
A) A specific piece of DNA is lifted from the infected cells from either side of where the lysogenic phage had integrated into the host cells. These sequences are then encapsulated and transported to other cells and integrate in the newly infected cells at the viral integration site.
B) Any piece of DNA can be transferred from one infected cell to another if it is randomly incorporated into the capsid when the virions are assembling.
Generalized transduction: Any piece of DNA can be transferred from one infected cell to another if it is randomly incorporated into the capsid when the virions are assembling.
Specialized transduction: A specific piece of DNA is lifted from the infected cells from either side of where the lysogenic phage had integrated into the host cells. These sequences are then encapsulated and transported to other cells and integrate in the newly infected cells at the viral integration site.
In other words for specialized transduction; specific piece of DNA that is being taken from the phage to phage convert is repackaged inside phage when in a lytic cycle and can phage convert other cells as well.
