Flashcards in Ex2- Transfer of Genetic Information Deck (51):
How do Bacteria reproduce by binary fission?
In this process, the chromosome of the mother cell is replicated and a copy is allocated to each of the daughter cells. As a result the two daughter cells are genetically identical.
What events can result in a heritable changes in the genomes?
The events that are able to causes changes in heritable genomes to daughter cells are genetic transfer and recombination, plasmids and transposons.
What is genetic transfer and in what direction does it occur?
genetic transfer is the mechanism by which DNA is transferred from donor to recipient. This always occurs in unidirectional and partial.
In what 3 ways can Genetic transfer Happen
3 ways Genetic transfer can occur are by:
What is conjugation?
-Conjugation: The movement if DNA through a plus by action of the F' fertility factor.
What is Transduction/Tranfection?
Transduction/Transfection: the use of a virus vector to deliver the DNA into the target cell such as the lambda phage,P1.
What is Transformation?
Transformation: The direct uptake of naked DNA by the cell. Does not happen very often.
What are the main characteristics of Bacterial conjugation?
-donor strains contain an additional genetic element, called the fertility factor F+,which carries the plasmid that encodes the transformation machinery.
- F+ strains mate with F- strains
- DNA transfer occurs unidirectionally from the F+ to the F- with a partial transfer.
What are some interesting factors of the F' fertility factor?
-Much larger than the average plasmid
-It can relocate both through the rolling-circle and normal double stranded (theta structure) replication
-Can replicate into the host chromosome , which allows for the transfer of part or all of the donor chromosome to the recipient
What are the key areas of the F' site.
The key areas include:
What is important of the key area of the F' oriT?
oriT is the origin of transfer, this is wren the F' is nicked in order to start rolling replication
What is important of the key areas of the F' Tra genes?
Tra genes include traA, traY, and traI.
-traA; pillin protein , which makes the sex plus for conjugation
-traY; nicks that initiates the rolling circle
What is important of the key areas of the F' insertion sequences
These sequences encode for proteins specific for insertion into the host chromosome.
What is important of the key area of the F' oriV?
oriV is the origin for double stranded, normal DNA replication
How does Bacterial Conjugation occur?
- F+ male will produce a pili and search for a female cell. Conjugation is then initiated when the pilus binds to the OmpA
receptor. They are then stabilized by the actions traN and traG gene and the plus retracts thus brining the other cell into closer proximity establishing a membrane enclosed channel between donor and the recipient.
What does not allow for the male F+ cell to mate with other F+ cells?
Because of the presence of TraT and TraS proteins.
TraT; causes an abundance of outer membrane proteins that causes surface exclusion.
TraS; is an inner membrane protein that presents the DNA exchange.
How do we create an F' strain?
A Hfr (High frequency of recombination) stain occurs when the F' factor becomes integrated into the E. coli host chromosome, due to the presence of the insertion sequences.
How does the insertion sequence allow for the creation of F strains
The insertion sequences allow the factor to line up with the same sequence on the host chromosome, and, via homologous recombination, integrate itself into the genome.
If the factor now undergoes rolling-circle replication, it will carry along with it some fragment of the host genome. In conjugation, this allows fairly long stretches of DNA to be recombined into the acceptor cell’s genome.
How are we able to create Hfr strains?
The F plasmid can integrate into the chromosome directed by transposon homology, by transferring the chromosome starting from the origin to its near by proteins. Crating a Hfr strain. This transfer continues until it is interrupted.
What is Transformation?
Transformation is the direct uptake of naked DNA by the cell from the environment.
Because Transformation does not occur naturally very often what are some tricks to cause this process to occur?
Tricks for transformation include Electrocompetence and Calcium competence.
How is Eletrocompetence used in the transformation process?
electrocompetence allows us to strip the cations off the cell surface, exposing naked negative charge. As electricity runs through the broth, it causes holes to open in the cell membrane this is known as electroporation, letting the DNA leak in.
How is Calcium competence used in the transformation process?
Calcium competence floods the outer membrane of the cell with calcium, so that the mutual repulsion of the positive charge destabilizes the cell membrane and the heat shock will allow the DNA to leak into the cell.
What is Transduction/ Transfection?
Transduction is a process in which a virus vector deliver the DNA into the target cell.
What cycle does the T4 hoagie use in comparison to the lambda phage?
T4 multiplies by the lytic cycle which kills the host and lambda multiplies by the lysogenic cycle which does not cause the death of the host cell, until it breaks out into the lytic cycle.
What are the general 5 steps of the lytic cycle?
1) attachment of the t4 receptor on E.coli
2) Penetration of the cell wall,as the tail core injects the DNA
3)E.coli DNA is hydrolyzed and thus the phage DNA directs the biosynthesis of the virus parts using the host cell machinery
4) The phage mature as the parts are assembled.
5)Lysses of the e.coli cell and release of the new phages
Why are regulatory genes important in the development of a large phage DNA. And what is the regulatory cascade?
Regulatory genes are responsible for the regulation of transcription, this regulation is known as the regulatory cascade. Each step triggers the next step and and stops the previous and allows maturation of the phage.
True or False: the phage DNA remains latent in the host cell until it breaks into the lytic cycle.
What is a prophage?
Prophage is a stse in lysogeny in which the phage DNA is integrated into the chromosomal DNA of the bacterium or replicates as a plasmid.
What is a lysogen?
A strain of bacteria that harbors a prophage
What is the lysogenic cycle?
A series of events that follow infection by a bacteriophage and culminate in the formation of a stable prophage.
What is a lysogenic phage?
It is a phage which is capable of entering the prophage state.
What are the 6 general steps of the lysogenic cycle?
1) Phage attaches to E. coli and injects DNA.
2) Phage circularizes and can enter either the lytic or the lysogenic cycle.
3) In the lysogenic cycle the circular phage DNA recombines with E. coli DNA and the phage DNA is now called prophage.
4) E. coli undergoes cell division, copying prophage and passing to daughter.
With more divisions there are more cells with the prophage.
5) The prophage may exit the chromosome and start a lytic cycle at any time.
6) The lytic cycle would occur as previously described.
Early genes do what?
Encode mostly enzymes involved in the DNA synthesis and it has promoters that mimic those of the host cell and are recognized by the RNA polymerase from the host.
Late genes do what?
Encodes the head and tail. The promoters not recognized by the host RNA plymerase alone from the host
__________, their products are responsible for regulation the transcription (turn on or off transcription of other genes)
______, is the regulation performed by regulatory genes
Regulatory cascade; each step triggers the next step and stops the preceding. All information for the development of the phage is preprogrammed into the phage DNA
The phage DNA that remains latent in the host until it breaks out in a lytic cycle is what?
_____, state of the phage in a lysogen in which the phage DNA is integrated into the chromosomal DNA of the bacterium or replicates as plasmid
______, a strain of bacteria that harbors a prophage
_____, a series of events that follow infection by a bacteriophage and culminate in the formation of stable prophage
_____, a phage which is capable of entering a prophage state.
What is phage transduction?
A genetic exchange in which bacteriophages carry bacterial genes from one host cell to another.
What are the two classes of transduction?
Generalized and Specialized
A fragments of host DNA are mistakenly packaged into a phage particle in place of its own DNA. WHen such a virus particle infects a new host cell, which DNA is injected into the host and can recombine with the host genome. What type of Transduction is it?
A lysogenic phage undergoes recombination with the host genome and later when it is excised to become an independent phage genome, it carries one or more host genes with it. These genes can be transduced into a new host cell and recombined into the genome of that cell. What type of Transduction is it?
What are the steps of general transduction? (6 steps)
1. A phage attaches to cell wall of bacterium and injects DNA
2. Bacterial chromosome is broken down and biosynthesis of phage DNA and protein occurs.
3. Sometimes bacterial DNA can be packaged into the virus instead of phage DNA (phage is defective and does not carry its own genetic material)
4. Cell lyses, releasing viruses
5. Phage carrying bacterial DNA infects another cell
6. Crossing over between donor and recipient DNA can occur producing a recombinant cell
What happens in generalized transduction?
Bacterial genes can be transferred because the host's chromosome is broken down into fragments
Specialized transduction requires a phage that uses what cycle for reproduction
In _____ only certain bacterial genes can be transferred