Ch 9
Which bacterial genetic transfer process does NOT require recombination with the bacterial chromosome?
F+ x F- conjugation
Competence factors
proteins that are needed for bacterial cells to naturally bind external DNA to the cell surface, and then transport it into the cytoplasm for incorporation into the bacterial chromosome.
Hfr strains of Escherichia coli
Hfr= High Frequency of Recombination. Capable of integrating into the bacterial chromosome. This is a cell in which the F factor has integrated into the host chromosome. Also called an episome
With regard to conjugation, a key difference between F+ and Hfr cells is that an Hfr cell?
Transfers a part of the bacterial chromosome to the recipient cell.
What is transformation?
When a bacterial cell dies, it releases a fragment of its DNA into the environment. This DNA fragment is taken up by a recipient cell, which incorporates the DNA into its chromosome by recombination.
Bacteriophage
viruses that bind to and infect bacteria
F factor
A fertility factor in bacteria; a DNA segment that confers the ability to form pili for conjugation and associated functions required for the transfer of DNA from donor to recipient. It may exist as a plasmid or be integrated into the bacterial chromosome.
horizontal gene transfer
A process in which an organism incorporates genetic material from another organism without being the offspring of that organism. -Conjugation, Transduction, and transformation are all examples of horizontal gene transfer.
Bacteria are usually _______________. This makes it easier to identify loss-of-function mutations in bacteria than in _______________.
Haploid eukaryotes These usually recessive mutations are not masked by dominant genes in haploid species.
A cell with an F factor integrated into the bacterial chromosome is called __________.
Hfr
In mapping experiments,_________________ strains are conjugated with F- strains. The distance between two genes is determined by comparing their ___________________ during a conjugation experiment.
Hfr and times of entry
When an F factor integrates into the chromosome, it creates a?
Hfr cell
What is conjugation?
involves the direct physical interaction between two bacterial cells. One bacterium acts as the donor and transfers the genetic material(known as a plasmid) to a recipient cell.
sex pili
rigid, tubular appendages that allow for the transfer of genetic material between bacterial cells. They are made by F+ strains
Plasmids are not necessary for bacterial survival. However in many cases certain genes within a plasmid provide?
some type of growth advantage to the cell
What is the first step of bacterial transduction?
1) A phage infects a bacterial cell by injecting its genetic material into the cell.
Bacteria can transfer genetic material in what three ways?
1) Conjugation 2) Transduction(Via bacteriophage) 3) Transformation
What is the first step in bacterial Conjugation?
1) contact is made, and the pili shorten and draw the recipient cell closer. A conjugation bridge is formed between the two cells which provide a passageway for DNA transfer.
What is transduction?
A virus infects a donor cell, a fragment of chromosomal DNA is incorporated into a newly made virus particle. The virus then transfers this fragment of DNA to a recipient cell, which incorporates the DNA into its chromosome by recombination.
A bacterial cell with an F factor conjugates with an F- cell. Following conjugation, the two cells will be?
F+
F' factors
F factors that carry a portion of the bacterial chromosome.
What is the second step of bacterial transduction?
2) Following infection, the bacterial chromosomal DNA is digested into pieces.
Test crosses are not used when studying?
Bacteria. They reproduce asexually so crosses cannot be used.
Most known plasmids are?
Circular but there are some known to be linear.
Fertility plasmids
Known as F factor plasmids, allow bacteria to conjugate with one another.
How is co-tranduction used to map genes?
a researcher selects for the transduction of one gene and then monitors whether or not a second gene is cotransduced along with it.
How did Wollman and Jacobs strategy of agitating at certain times assist them in their mapping strategy?
The time it takes for genes to enter a donor cell is directly related to the order along the bacterial chromosome starting at the origin of transfer. By hypothesizing that the genes are passed to the receiving cell in a linear manner the gene locations could be deduced by determining how long it took each of those genes to appear in the other cell.
Auxotroph
a strain that cannot synthesize a particular nutrient and needs that nutrient to be supplemented in its growth medium
generalized transduction
Transfer of any bacterial DNA to recipient cells
A form of genetic transfer that involves the uptake of a fragment of DNA from the environment is called?
Transformation
minimal medium
a defined medium that contains the minimal ingredients needed by genetically normal (wild type) strains of a particular species to grow.
Interrupted mating
a method used in conjugation experiments in which the length of time that the bacteria spend conjugating is stopped by a blender treatment or other type of harsh agitation
In transduction, the DNA is being moved between the two cells by ______.
a prophage
During transduction via a P1 phage
any small fragment of the bacterial chromosome may be transferred to another bacterium by the phage
Degradative plasmids
carry genes that enable the bacterium to utilize an unusual substance. For example, a degradative plasmid may carry genes that allow a bacterium to metabolize an organic solvent such as toluene.
What is the second step in bacterial Conjugation?
2) Genes within the F factor encode a protein complex called the relaxosome. This complex first recognizes a DNA sequence in the F factor known as the Origin of Transfer. Upon recognition, the relaxosome cuts one DNA strand at that site in the F factor.
What is the fourth step in bacterial conjugation?
4) Involves the export of the nucleoprotein complex from the donor cell to the recipient cell. To begin this process, the DNA/relaxase complex is recognized by a coupling factor that promotes the entry of the nucleoprotein into the exporter, a complex of proteins that spans both inner and outer membranes of the donor cell. In bacteria this complex is formed by 10-15 different proteins that are encoded by genes within the F factor.
What is the fourth step of bacterial transduction?
4) The bacterial cell is lysed and releases the newly made phages into the environment
What is the fifth step of bacterial transduction?
5) Following release, the transducing phage can bind to a living bacterial cell and inject its genetic material into the bacterium.
Which of the following is a type of plasmid? A) F factor B) R factor C) Virulence D) All of the above
D) All of the above
Prototroph
a strain that does not need a particular in its growth medium
What are episomes?
a type of plasmid that can integrate into the genome of the recipient cell. Ex: F factor
Competent cells
bacterial cells that are able to take up DNA naturally.
Virulence plasmids
carry genes that turn a bacterium into a pathogenic strain.
Co-transduction may be used to map bacterial genes that are?
close together on the bacterial chromosome.
Col-plasmids
contain genes that encode colicins, which are proteins that kill other bacteria.
In experiments, interrupted mating may be used to
determine the relative position of genes
The units of genetic distance derived from bacterial conjugation studies are called _____.
minutes
Specialized transduction
only particular bacterial genes are transferred to recipient cells. - Viral DNA integrates into the bacterial chromosome at a specific site. - When viral DNA is excised, it picks up a piece of chromosomal DNA by accident. -Usually lysogenic cycle
The site on a plasmid that is cut, producing a single strand of DNA, to allow conjugation to occur is called the ____________.
origin of transfer
Resistance plasmids (R plasmids)
resistance plasmids or R factors contain genes that confer resistance against antibiotics and other types of toxins.
The order of genetic transfer depends on?
the location and orientation of the origin of transfer.
Co-tranduction
the process by which two genetic markers are simultaneously packaged within a bacteriophage for transfer to a new host bacterium. This only works for genes that are close together because the bacteriophage cannot physically package a DNA fragment that consists of more than 1%-2.5% of the bacterial chromosome.
What is the third step of bacterial transduction?
3) New phage proteins and DNA are made and begin to assemble into new phages. Occasionally, a mistake is made and a random piece of bacterial DNA is assemble with phage proteins. This creates a transducing phage that contains bacterial chromosomal DNA.
What is the third step in bacterial Conjugation?
3) The relaxosome also catalyzes the separation of the DNA strands, and only cut the DNA strand, called T DNA, is transferred to the recipient cell. As the DNA strands separate, most of the proteins within the relaxosome are released, but a protein called relaxase remains bound to one end of the cut DNA strand.
What is the fifth step of bacterial conjugation?
5) Once the DNA/relaxase complex is pumped out of the donor cell, it travels through the conjugation bridge and then into the recipient cell. The other strand of the F-factor DNA remains in the donor cell where DNA replication restores this DNA to its original double-stranded condition. After the recipient cell receives a single strand of the F factor DNA, relaxase catalyzes the joining of the ends of this linear molecule to form a circular molecule. This single stranded DNA is replicated in the recipient cell to become double stranded.
What is the sixth and final stage of bacterial transduction?
6) The DNA fragment, which was derived from the chromosomal DNA of the first bacterium, can then recombine with the recipient cell's chromosome.
