Involves the transfer of genetic material from one bacteria to another.
RECOMBINATION
Recombination refers to the exchange of genes between 2 DNA molecules or between different parts of the same molecule. This results in new combinations of genes or genetic information on the chromosomes involved. Show There are four ways in which recombination occurs in bacteria:
This was originally observed by Griffith in 1928 and the mechanism was worked out in experiments by Avery, MacLeod and McCarty in 1944. These experiments showed that
Not all bacteria are as capable of Transformation. In the lab cells can be made competent by treatment with CaCl2. Gene guns have also been developed to shoot or inject DNA into cells. Electroporation involves treating cells with an electric field which helps them to take up DNA. CONJUGATION (Fig. 8.26, pg. 215) -- The transfer of genetic information through direct Cell-to-Cell contact. This process is controlled by genes found on plasmids and "sex pili." Define Plasmids -- extrachromosomal, circular pieces of DNA which can replicate independently A plasmid called the F factor or the fertility factor is an example of how conjugation works:
There are many types of plasmids that can be passed through conjugation:
In transduction, bacterial DNA is transferred between bacteria through bacterial viruses. (See fig. 8.27 on page 216). See pg. 333, Table 13.1 - A Comparison of Viruses to Bacteria. See pg. 334, Fig. 13.1 - Comparison of Viruses to Bacteria and Human Cells. Virus Structure: (See pictures on pgs. 335,336 and 337). Note the genome, the capsid, the capsomeres, the envelope, the spikes or peplomeres. Nonenveloped viruses are often called naked viruses. Bacterial viruses are also called phage or bacteriophage. (See the example of the T-even phage on page 337.) Viruses are obligate intracellular parasites. There are viruses which infect bacterial cells as well as plant cells and animal cells. Each virus species however does have a very specific host range -- there are phage which are specific for E. colior . aureusas well as for particular strains of E. colior Staph. aureus. Also, many human viruses are very specific and selective about which human tissues they infect -- for instance HIV infects human CD4+ cells (primarily helper T-cells) and hepatitis B virus infects hepatocytes. There are two fundamental types of viral life cycles:
The Lysogenic Viral Life Cycle (See pg. 346, Fig. 13.16) These viruses may be (1) lytic or they (2) may infect the cell in a dormant manner. By dormant we understand that the viral genome recombines with the host genome. We say that the viral genome becomes integrated into the host genome. When integrated the viral genome is called a prophage or a provirus.Animal Viruses Animal virus life cycles are very similar to the bacterial ones described above. Many animal viruses which cause acute diseases with rapid onset, usually with dramatic symptoms and quick resolution (either for the good or the harm of the patient) are lytic viruses. Influenza virus and Ebola virus are two examples. Many other animal viruses cause latent, and also persistant and chronic infections. In latent infections the virus is invisible -- no virus is made and infected cells look healthy. Persistently or chronically infected cells produce virus particles at a low rate and such cells may live for many years. These infections are very similar to the lysogenic infections discussed above. Examples of these lysogenic animal virus infections include:
fever blisters nasopharyngeal carcinoma (See pg. 348, fig. 13.18; pg. 524, fig. 21.9)
- HTLV-2 -- hairy cell leukemia (See pg 352, fig. 13.21; figs. and tables on pgs. 480-485) As you can see above, several of these lysogenic animal viruses have been associated with cancer. The development of cancer appears to take several steps -- at least a couple of different mutations; or in the case of the oncogenic (cancer causing) viruses above, a mutation plus a virus infection. All animal cells have genes which control their growth and differentiation. Many of these genes are oncogenes (c-oncogenes) because if they are expressed abnormally they cause:
How do such genes come to be expressed abnormally? Either through (1) mutation or (2) through infection with oncogenic viruses carrying mutated oncogenes (v-oncogenes).Cells have mechanisms to protect themselves from damaged or foreign malignant DNA. In addition to the regular DNA repair enzymes, there are tumor suppressor genes and their protein products. p53 is such a gene (and protein) which examines the genome and detects damage. p53 stops cell division until the DNA is repaired. If the genome cannot be repaired, p53 triggers apoptosis (programmed cell death). What is the genetic material transferred between bacteria?Conjugation is the process by which one bacterium transfers genetic material to another through direct contact. During conjugation, one bacterium serves as the donor of the genetic material, and the other serves as the recipient. The donor bacterium carries a DNA sequence called the fertility factor, or F-factor.
What is the transfer of genetic material?Human gene transfer (therapy) is the process of transferring genetic material (DNA or RNA) into a person. Gene therapy is a medical intervention based on modification of the genetic material of living cells which is then given to humans.
What is the name of the genetic material that can be transferred from one bacteria to another one replicated independently that carry genes that encode the virulence factors?The transfer of genetic material from a donor bacterium to a recipient bacterium via phages is called transduction. Phages are viruses (bacteriophage) that break down or lyse bacteria.
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