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Chapter_28_lecture_RAVEN_NG2009 (1)

when conditions improve they can germinate and

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Unformatted text preview: ly heat. -When conditions improve, they can germinate and return to normal cell division to form new individuals eg. Bacteria causing tetanus, anthrax, ... are capable of forming spores. With a puncture wound, endospores are driven deep in skin => favorable conditions for germination and causing disease or even death. 14 Prokaryotic Genetics Prokaryotes do not reproduce sexually However, they undergo horizontal gene transfer, which is (Genes can move from one cell to another through): of three types -Conjugation = Cell-to-cell contact -Transduction = By bacteriophages -Transformation = From the environment picking up of genetic material All of these processes have been observed, alongside Bacteria, in Archaea Note: 15 Vertical gene transfer: Sexual reproduction (from parent to child/generation to generation) Conjugation Plasmids can be transferred from one cell to another via conjugaton The best-known plasmid capable of transfer is the F plasmid In E. coli, conjugation is based on the presence of the F plasmid F+ cells contain the plasmid F- cells do not The F+ cell produce an F pilus that connects it to an F- cell Note: The F plasmid, like all plasmids, acts as an independent genetic entity that nevertheless depends on the cell for replication. 16 F plasmid: fertility plasmid/ fertility factor Conjugation The conjugation bridge is assembled by plasmid genes that encode proteins on the surface of the bacterial cell, leading to the formation of a pilus Transfer of the F plasmid occurs through the conjugation bridge The end result is two F+ cells 1. The F plasmid binds to a site on the interior of the F+ cell beneath the F pilus (conjugation bridge). 2. By a process called 'Rolling-circle replication,' the F plasmid copies its DNA at the binding point. 3. As it is replicated, the displaced single strand of the plasmid passes into the other cell. 4. A complementary strand is added => new, stable F plasmid. 17 host The F plasmid can integrate into the bacterial chromosome by recombining with it homologous recombination This integration is mediated by host-encoded proteins A cell in which the F -Hfr cell (high frequency of recombination) plasmid has been integrated into the chromosome is called since transfer by plasmid will now include chromosomal DNA The F plasmid can also excise itself by reversing the integration process IS: insertion sequence read p.549 18...
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