In generalized transduction, a bacterial host cell is infected with either a virulent or a temperate bacteriophage engaging in the lytic cycle of replication. There are two different types of transduction: generalized transduction and specialized transduction. Transduction involves the use of a virus, a bacteriophage, to act as a conduit for shuttling bacteria genes from one cell to another, thus negating the necessity for cell-to-cell contact. Once inside the cell, the DNA must be incorporated into the bacterial chromosome by RecA (see Molecular Recombination below), for the genes to be expressed. An endonuclease can be used to degrade one strand of dsDNA, if only ssDNA may pass into the cell, or to cleave the DNA fragment into smaller sizes. Random pieces of DNA bind to receptors on the outside of the cell and are then transported into the cell by the DNA translocase, through the transmembrane channel, a large structure often involving numerous different proteins. Gram negative cells also make a cell wall autolysin, to transport the DNA across the outer membrane. Under these conditions specific proteins are manufactured including DNA-binding proteins ( DNA translocase), endonucleases, and transmembrane channel proteins. The process typically occurs at the end of exponential phase of growth or beginning of the stationary phase, in the presence of high cell density and limited nutrients. There are mechanical and chemical means of encouraging a cell to pick up DNA from the environment, but natural competence is determined genetically. The recipient cell is one that is capable of taking up the DNA from the environment and incorporating it into its own genome, where the cell is described as being competent. Typically the process requires a donor cell that at some point lysed and released naked DNA to the environment. In this process the new genes are acquired directly from the environment. The process of transformation also allows a bacterial cell to acquire new genes, but it does not require cell-to-cell contact. By Adenosine (Own work), via Wikimedia Commons Transformation Both cells then make the complementary copy to the ssDNA, resulting in two F+ cells capable of conjugation. It is believed that a channel is then opened between the two cells, allowing for a ssDNA copy of the plasmid to enter the recipient cells. The pilus is used to bind to the recipient ( F-) cell, bringing it in close proximity to the donor cell. The donor cell ( F+) has a conjugative plasmid, an extrachromosomal piece of dsDNA that codes for the proteins necessary to make a threadlike filament known as a pilus. The process requires cell-to-cell contact. ConjugationĬonjugation is the process by which a donor bacterium transfers a copy of a plasmid to a recipient bacterium, through a pilus. But where would these genes come from? How would the bacteria get a hold of them? We are going to explore the processes that bacteria use to acquire new genes, the mechanisms known as Horizontal Gene Transfer (HGT). Which presents a real problem for bacteria (and archaea, too) – how do they get the genetic variability that they need? They might need a new gene to break down an unusual nutrient source or degrade an antibiotic threatening to destroy them – acquiring the gene could mean the difference between life and death. Ha! That is going to be difficult, since bacteria do not have sex. The history of genetics can be divided into two phases: one before and the other after 1953, the year in which the structure of DNA, the molecule of life, was discovered.Let’s talk about sex.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |