Genetic Transfer Systems Flashcards
What are the THREE mechanisms that bacteria are able to acquire genetic information from their environment or from each other?
- Conjugation
- Transformation
- Transduction
What is Conjugation?
Transfer of DNA involving direct cell-to-cell contact mediated by pili
What is Transformation?
Uptake of free exogenous DNA by a bacterium
What is Transduction?
Transfer of DNA from one bacterium to another by a bacteriophage
What are the THREE outcomes for recieved DNA?
- Exist autonomously in cytoplasm of recipient
- Integrated into recipient chromosome
- Replace homologous DNA of recipient
What is the Recipient?
Bacterium that RECIEVES DNA
What is the Donor?
Bacterium that DONATES DNA
What is Homologous DNA?
Regions of DNA which are very similar between donor and recipient
Can DNA move unidirectionally or bidirectionally between bacterium?
DNA always moves in one direction
What do a Donor and Recipient together make?
Mating pair
What factor do E. coli donor cells contain?
F-factor
What is an F-factor?
Genetic element (plasmid or episome) capable of conjugative transfer
How many genes are contained in an F-factor?
20 tra genes, involved in DNA transfer
What proteins do tra genes encode for?
Proteins required for the synthesis of specialised appendages (e.g. Pili)
What are the functions encoded by the F-plasmid?
- Attach donor to recipient
- Provide a channel through which genetic material can be passed
- tra genes also confer surface properties on donors that prevents contact with other donors
What THREE forms can an F-factor exist in within a Donor?
- F+ donor
- Hfr bacterium
- Fâ donor
How does the F+ factor exist within a Donor?
Exists as small covalently closed circle of DNA within the cytoplasm
How does the Hfr factor exist within the Donor?
F plasmid is integrated into the bacterial chromosome, mobilising the entire bacterial genome
How does the Fâ factor exist within the Donor?
May contain a few other genes in a circular structure that exists free in the cytoplasm
What does the endonuclease (TraI) do in Conugation?
Puts a single break (or nick) in one of the two strands at the oriT, freeing one of the two DNA strands in the plasmid to begin DNA transfer to recipient
Do Transducing Phage contain DNA, RNA, or both?
Only DNA
What are the TWO different types of Transduction?
- Generalised
- Specialised
How is Generalised Transduction carried out?
By virulent DNA-containing phage that have a lytic cycle of infection
What is Generalised Transduction used for?
- To measure the distance between two bacterial genes
- Done by determining how frequently two genes are included in the same transducing phage
What does the distance between two genes included in the same transducing phage indicate?
The closer together two genes are on the chromosome, the more frequently they will be included in the same piece of transducing DNA
What ability of the cell will depend on whether it can undergo Transformation or not?
Whether the cell is Competent
How can E. coli become Competent?
Through CaCl2 or LiCl2 treatment, or electroporation
Who discovered the phenomenon of natural transformation?
Frederick Griffith
Who showed that natural transformation was due to DNA that was taken up by the cell?
Oswald Avery
What methods can produce Artificial Transformation?
- Chemical treatment
- Electroporation
- Protoplast formation
- Firing DNA-coated metal pellicles
