Chapter 7 Genetic Enginnerring
1, How does gene exchanged in bacteria?1,Lateral gene transfer (LGT) is any process in which an organism transfers genetic material (i.e. DNA) to another cell that is not its offspring.
2,vertical transfer occurs when an organism receives genetic material from its ancestor, e.g. its parent or a species from which it evolved.
2, Gene transfer in Prokaryotes?
Horizontal gene transfer is common among bacteria, even very distantly-related ones. This process is thought to be a significant cause of increased drug resistance; when one bacterial cell acquires resistance, it can quickly transfer the resistance genes to many species.
three common mechanisms for horizontal gene transfer:
- Transformation, the genetic alteration of a cell resulting from the introduction, uptake and expression of foreign genetic material (DNA or RNA). This process is relatively common in bacteria, but less common in eukaryotes. Transformation is often used to insert novel genes into bacteria for experiments, or for industrial or medical applications. See also molecular biology and biotechnology.
- Transduction, the process in which bacterial DNA is moved from one bacterium to another by a bacterial virus (a bacteriophage, commonly called a phage).
- Bacterial conjugation, a process in which a living bacterial cell transfers genetic material through cell-to-cell contact.
horizontal gene transfer has also occurred within eukaryotes, from their chloroplast and mitochondrial genome to their nuclear genome. chloroplasts and mitochondria probably originated as bacterial endosymbionts of a progenitor to the eukaryotic cell. Horizontal transfer of genes from bacteria to some fungi, especially the yeast Saccharomyces cerevisiae has been well documented.
4,Describe Griffith's experiments that led to the discovery of the transforming factor.
Griffith's experiment was conducted in 1928 by Frederick Griffith which was one of the first experiments suggesting that bacteria are capable of transferring genetic information, otherwise known as the “transforming principle”, which was later discovered to be DNA. Griffith used two strains of Pneumococcus (which infects mice), a S (smooth) and a R (rough) strain. The S strain covers itself with a polysaccharide capsule that protects it from the host's immune system, resulting in the death of the host, while the R strain doesn't have that protective capsule and is defeated by the host's immune system.
In his experiment, bacteria from the S strain were killed by heat, and their remains were added to R strain bacteria. It turned out that the formerly harmless R strain now was able to kill its host. It had been transformed into the lethal S strain, obviously by a transforming principle that was somehow part of the dead S strain bacteria.
Today, we know that the DNA of the S strain bacteria had survived the heating process, and was taken up by the R strain bacteria. The S strain DNA contains the genes that form the protective polysaccharide capsule. Equipped with this gene, the former R strain bacteria were now protected from the host's immune system and could kill it.
5, what is genetic recombination?
is the transfer of DNA from one organism to another. The transferred donor DNA may then be integrated into the recipient's nucleoid by various mechanisms.
6, what is transformation? what is transduction? what is conjungation? what do plasmid do?
Transformation is the uptake of a DNA fragment from the surrounding environment and the expression of that genetic information in the recipient cell, which the recipient has acquired a characteristic that is previously lacked.
1, A donnor bacterium disintegrates and liberates its DNA fragments into the surrounding environment.
2, A competent, live bacterium takes up a fragment of the DNA containing a few genes. The fragment travels through the cell wall and membrane of the recipient bacterium.
3, the fragment enters the recipient's cytoplasm.
4, in the cytoplasm, enzymes degrade one strand of the DNA helix. Stimultaneously, an enzyme degrades a strand from the a strand from the recipient's chromosome.
5, the strand of donor DNA replaces the strand of the recipient DNA, and the trnsformation is complete. Reproduction of the bacterium by binary fission will lead to a population of the transformed bacteria.
the mechanism for DNA transfer involes 1----binding of the DNA fragment, 2----passage of a single-strand molecule into the recipient, and 3-----incorporation into the bacterial chromosome.
8, what are hfr cells? what is the f plasmid? what is the R plasmic? what is the RTF plasmic?
hfr cell----is a bacterium with a conjugative plasmid (often F) integrated into its genomic DNA. Genetic recombination in which fragments of chromosomal DNA from a male donor bacterium are transferred to a female recipient bacterium following insertion of an F+ plasmid into the nucleoid of the donor bacterium. Involves a sex (conjugation)pilus.
http://student.ccbcmd.edu/courses/bio141/lecguide/unit4/genetics/recombination/conjugation/hfr.html
f plasmid-----A plasmid coding only for a sex pilus. a double-strand of loop of DNA existing apart from the baterial chromosome.
R plasmic-----A plasmid having genes coding for multiple antibiotic resistance and often a sex pilus.
RTF plasmic
7, what is conjungation?
Conjugation is the transferof DNA from a living donor bacterium to a recipient bacterium. In Gram-negative bacteria, a sex pilus (def) produced by the donor bacterium binds to the recipient. The sex pilus then retracts, bringing the two bacteria in contact. In Gram-positive bacteria sticky surface molecules are produced which bring the two bacteria into contact. DNA is then transferred from the donor to the recipient.
(a)conjugation between an F+ cell and an F- cell, when the F plasmic is transferred from a F+ donnor cell, the F- cell becomes an F+ cell as a resulte of the presence of an F plasmid.
1, conjugation sex pilus connects the F+ to the F- cell. 2, rolling circle replication and transfer of F- factor from the original of the transfer. (oriT) 3, Both cells now are F+.
(b)conjugation between an hfr cell and an F- cell, allows for the transfer of some chromosomal DNA from donor to recipient cell.
1, the hfr donor cell has the F plasmic integrated into the donor's chromosomes. 2, a sex pilus forms between the donor and the recipient cells, and replication of one strand of the donor's DNA begins a t the oriT site and passes into the recipient cell. 3, usually only a portion of the donor DNA enters the recipient cell before the conjugation strand replaces a complementary portion of the recipient's DNA. The recombnination is now complete, and the new genes can be expressed by the recipient.
8, What is transduction?
Transduction is the transfer of fragments of DNA from one bacterium to another bacterium by a bacteriophage (def).( a virus that infects and replicates within a bacterium. There are two types of transduction: generalized transduction and specialized transduction.
Generalized transduction:: durng reasnduction, a virus carries random DNA fragments from a donor bacterium to a recipient bacterium. The DNA fragment may recombine with the recipient cell.
1, the process of transduction begins when a virulent bacteriophage attaches to the surface of a host bacterial cell.
2, the DNA from the virulent phage enters the cytoplasm of the bacterium.
3, the viral DNA multiplies by encoding additional strands of phage DNA, as well as other phage protein components. The host DNA is fragmented in small piecies.
4, during replication, a bacterial DNA fragment accidentally gets packaged into a phage head during phage replication, producing a defective phage particle. most phage particles contain the normal phage DNA.
5, at the end of the replication process, all the new phage particles are repleased from the bacterium.
6, the virulent phage particles will go to to replicate in their host bacterial cells and have no bearing on transduction. transduction occurs when a defective phage interacts with a bacterial cell.
7, the phage DNA enters the host cell. but note that the DNA is bacterial DNA not the normal phage DNA.
8, the bacterial DNA fragment does not encode new phage particles but it can intergrate into the bacterial DNA and transduce the cell. Thus, the new host cell has acquired DNA from another bacterium.
Specialized transduction: a virus carries specified genes from a donor bacterium to a recipient bacterium. the process involves lysogeny and results in a recombinant cell.
1, specialized transduction begins as a temperate bacteriophage attaches to the surface of a host bacterial cell.
2, the DNA of the temperate phage enters the bacterial cytoplasm.
3, the viral DNA integrate into the bacterial DNA. now it is called a prophage. Here the prophage has inserted between bacterial genes A and D. Bacteria can undergo binary fission with each new cell carry the prophage.
4, at some point later, the prophage is cut of the bacterial DNA and phage DNA replication occurs as a lytic cycle.
5, if the prophage excision is precise, new temperate virus will form.
6, if the excision is not precise, the prophage will alone some of bacterial DNA. so the new phage each carry gene D from the donor bacterium.
7, later, the defective virus finds a new bacterial host cell.
8, the DNA enters the host cell cytoplasm.
9, the viral DNA integrates with the bacterial DNA in the process of lysogeny. but in doing so, through recombination gene D from the previous bacterium also integrates into the recipients cell;s chromosome. the recipiente cell thus acquires a gene from the dono bacterium and is transduced.
9, explain the unique place of the virus in the process of bacterial transduction; what is the result in the terms of disease? examples?
Transduction requires a virus to carry the DNA fragment from donor to recipient cell. The virus that participates in reansduction is called a bacteriophage, or simply phage.it was assumed to ba s type of poisonbecause they dissolve bacteria. today we recoginize them as viruses composed of a core of DNA or RNA surrounded by a coat of protein. phages that participate in transduction are transducing phage. In the replication cycle of a bacteriophage, the phage interacts with bacteria in two ways. 1, the phage invades the bacterium, then replicates itself and destroys the bacterium as new phage are replease---lytic cycle. phages that cause lysis is virulent phages. 2, phage interact with bacteria also involves invasion of the bacterium but without cell lysis. in this case, the phage DNA encodes a repressor protein that inhibits its own replication. The phage DNA often forms a closed circle that alogns next to the bacterial chromosome before integrateing into the bacterial chromosome. this process is called lysogeny. and the phages that participage in lysogeny is temperate phages.
10, what is genetic engineering?
the use of bacterial and microbial genetics, including the isolation, manipulation, and control of gene expression had far-reaching ramifications, leading to an entirely new field.
posted by C-T @ 3:36 PM
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