Lecture 41. Plasmids and Conjugation Flashcards
What is conjugation?
Conjugation is the process of moving genetic material (often, but not always, plasmids) via direct cell-to-cell contact
What do the Lederberg and Tatum experiment and the Davies experiment show?
Reversion to wild type bacteria must require cell-to-cell contact
Plasmids
Almost always double stranded
DNA Most are circular, but they can be linear
Size 1 kb to >1Mbp
Replicate independently of chromosomal DNA
Do not have extra cellular form like phages
Can plasmids have different copy numbers within the same host?
Yes
Why are some plasmids incompatible?
Related plasmids sharing common mechanisms of replication often cannot coexist
What are episomes?
Special plasmids that can integrate into host genome
What is curing?
When a plasmid is lost from a host - can happen spontaneously or in response to certain chemicals
What are the roles of plasmids?
They carry non-essential but often highly useful genes
What are conjugative plasmids?
Plasmids that encode genes that will allow transfer to other cells
What does the F pilus do?
It allows unidirectional transfer of DNA from donor to recipient
Process of plasmid making contact
- Donor looking for mate
- Contact is made
- Cells pull closer
- Transfer of plasmid via mating bridge
- Both cells now have plasmid
How is the plasmid transferred?
As single stranded DNA after being nicked and “unrolled” into recipient cell
How is the plasmid copied?
By Rolling Circle Replication (RCR)
What does F stand for?
Fertility factor
Where can the F plasmid spread rapidly?
F plasmid can spread through an F- culture rapidly ensuring all cells are converted to F+
