This preview shows page 1. Sign up to view the full content.
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
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...
View Full Document