Unit 5 pt. 2 Flashcards
Define horizontal gene transfer
The transfer of genetic information between organisms in the same generation
What are the 3 types of horizontal gene transfer that occur in bacteria?
Transformation
Transduction
Conjugation
Define Transformation
The process by which a cell takes up foreign DNA from its environment and incorporates it into its own
Define Transduction
The process by which bacterial DNA is transferred from one bacterium to another via a bacteriophage
Define Conjugation
DNA is transferred from one living bacterial cell to another with the sex pilis;
the cells must touch and after the process both cells have their own copy of the transferred DNA
What do all 3 of these mechanisms involve? (transformation, transduction, conjugation)
A donor cell that transfers a portion of its DNA to a recipient cell;
which may incorporate the new DNA into its own becoming a recombinant organism
A recombinant cell is a cell that receives DNA _____
from an outside source and incorporates it into its own
What is the hallmark of all horizontal gene transfers?
(basic definition)
Transfer of DNA between organisms of the same generation
What does it mean when a cell is competent?
can take up DNA from their surrounding environment and integrate it into their own chromosomes by recombination
Cells of a smooth strain produce a capsule that allows them to escape ______________
phagocytosis by the body’s defensive white blood cells
(unlike rough strain)
What can be used to kill the smooth strain?
Heat
S (heat-killed) cells when injected = mice live
R (live) + S (heat-killed) cells =
(both harmless)
death; s strain found in blood
because the harmless rough strain cells must have gained the genes to produce capsules like those of the virulent s strain cells
Mice that are injected with only the R strain of Streptococcus pneumoniae ___
stay healthy, because their immune systems can kill this strain easily
What characteristic of the S strain allows it to evade the immune system of the mice?
The cells have a capsule
What most likely explains the recovery of live S strain cells from a mouse injected with heat-killed S strain mixed with live R strain cells?
The R strain picked up the S strain DNA, enabling it to produce a capsule
Which finding is most surprising from Griffith’s experiments?
S strain cells are isolated from the blood of mice infected with heat-killed S strains and live R strains
Bacterial conjugation is often referred to as bacterial sex. Why is this term inaccurate?
Conjugation does not result in the formation of new offspring
What must occur for bacterial conjugation to take place?
The cells must come into contact with each other
Which statement about conjugation is false?
a. E. coli is the model for bacterial conjugation.
b. Conjugation is a process of bacterial reproduction.
c. After conjugation, each cell involved has a copy of the shared DNA.
b. Conjugation is a process of bacterial reproduction.
What is transferred during bacterial conjugation?
A bacterial plasmid
What are cells containing an F factor called?
F+ cells;
they serve as DNA donors during conjugation
What is an F factor?
Fertility factor or F plasmid
What are conjugation pili or sex pili?
proteinaceous, rod like structures;
formed by (E. coli) cells containing an F factor
What are cells lacking the F plasmid called?
F- cells;
they serve as DNA recipients during conjugation
What happens at the start of conjugation?
A conjugation pilus extends from an F+ cell to an F- cell and pulls the cells together
What happens in conjugation after the cells are pulled together by the pilus from the F+ cell?
The cells come together and stabilize, probably through fusion of their cell membranes then the transfer of DNA begins
What is transferred between conjugation of F+ and F- cells?
A single stranded copy of the F factor is transferred from the F+ cell to the F- cell
Each cell synthesizes a complementary strand of the plasmid resulting in a complete copy of the plasmid in each cell
What do both cells contain after conjugation of F+ and F- cells?
A copy of the F factor therefore both cells are now F+ cells and can go on to initiate conjugation with other F- cells
What is the function of the conjugation pilus?
It pulls the F+ and F- cells together
What is required by an F- cell to become an F+ cell?
F plasmid
What is the key difference between donor cells and recipient cells?
An F plasmid (donor cell has)
What cellular macromolecule is the fertility factor comprised of?
Nucleic acid
At which point does a recipient cell become an F+ cell?
Formation of the complementary strand of the F factor
How is F+ cell converted into a Hfr?
A(n) ______ integrates into the E. coli _____
An F factor integrates into the E. coli chromosome
How are F+ and Hfr cells similar?
They both form conjugation pili which attach to F- cells
Where does the DNA transfer begin with Hfr and F-?
In the middle of the F factor within the Hfr cell’s chromosome;
usually the chromosome breaks before it is completely transferred
What is the result of the Hfr’s chromosome breaking before it is completely transferred?
The F- cell does not receive a full copy of the F factor;
because of this it remains F- however the DNA from the donor can recombine with the recipients chromosome giving the recipient new chromosomal genes
How does an F+ cell differ from an Hfr cell?
Hfr strains have the F plasmid integrated into the chromosome
Why does conjugation between an Hfr strain and an F- strain not result in two Hfr strains?
Conjugation is typically disrupted before the fertility factor can be transferred
What are 3 characteristics of a F+ cell?
- Ability to synthesize sex pili
- Presence of a fertility factor
- Ability to mate with an F- cell
What benefit does the F- strain receive from mating with an Hfr strain?
It acquires new, potentially beneficial genes from the Hfr strain
A mutation that causes production of a defective pilus in a bacterium will prevent __________
Conjugation
What was the scientific result of Frederick Griffith’s experiments with Streptococcus pneumoniae?
He showed that the DNA from strain S cells could transform strain R cells
