Snyder molecular genetics of bacteria pdf

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This is an illustration of the difference between generalized transduction, which is the process of transferring any bacterial gene to a second bacterium through a bacteriophage and specialized transduction, which is the process of moving restricted bacterial genes to a recipient bacterium. While generalized transduction can snyder molecular genetics of bacteria pdf randomly and more easily, specialized transduction depends on the location of the genes on the chromosome and the incorrect excision of the a prophage. DNA or RNA and the protein coat. The lytic cycle leads to the production of new phage particles which are released by lysis of the host.

The packaging of bacteriophage DNA has low fidelity and small pieces of bacterial DNA, together with the bacteriophage genome, may become packaged into the bacteriophage genome. At the same time, some phage genes are left behind in the bacterial chromosome. There are generally three types of recombination events that can lead to this incorporation of bacterial DNA into the viral DNA, leading to two modes of recombination. In essence, this is the packaging of bacterial DNA into a viral envelope. This may occur in two main ways, recombination and headful packaging. If the virus replicates using ‘headful packaging’, it attempts to fill the nucleocapsid with genetic material.

If the viral genome results in spare capacity, viral packaging mechanisms may incorporate bacterial genetic material into the new virion. The new virus capsule now loaded with part bacterial DNA continues to infect another bacterial cell. This bacterial material may become recombined into another bacterium upon infection. The DNA will be absorbed by the cell and be recycled for spare parts. If the DNA was originally a plasmid, it will re-circularize inside the new cell and become a plasmid again. Specialized transduction occurs when the prophage excises imprecisely from the chromosome so that bacterial genes lying adjacent to the prophage are included in the excised DNA. The excised DNA is then packaged into a new virus particle, which then delivers the DNA to a new bacterium, where the donor genes can be inserted into the recipient chromosome or remain in the cytoplasm, depending on the nature of the bacteriophage.

DNA is called a “heterogenote”. In these cases, a plasmid is constructed in which the genes to be transferred are flanked by viral sequences that are used by viral proteins to recognize and package the viral genome into viral particles. For safety, none of the plasmids used contains all the sequences required for virus formation, so that simultaneous transfection of multiple plasmids is required to get infectious virions. Moreover, only the plasmid carrying the sequences to be transferred contains signals that allow the genetic materials to be packaged in virions, so that none of the genes encoding viral proteins are packaged.