Genetics 2 - exchange of genetic material Flashcards
What are mutations?
heritable characteristics in the genome
Why is exchange of genetic material useful?
exchange of genetic information between microbes enables genomes to develop more rapidly than by mutation alone
What are the process in bacteria that allow the transfer of genetic information from donor to recipient?
horizontal gene transfer
transformation
transduction
conjugation
What is the process of transformation?
- DNA is released by the donor bacterium (dead and degraded) into the environment = lysis
- recipient bacterium takes up DNA from the extracellular environment directly = membrane is made more permeable
- exogenous DNA (genetic material) is incorporated into the cell
- homologous recombination of the recipient and donor cell DNA
the bacteria must be competent
DNA must be at least 500 nucleotides in length
What does a competent bacterium mean?
a competent bacterium
- is capable of taking up exogenous DNA (plasmid) = pores are created in the cell
What is the process of transduction?
bacteriophage function as a vector to introduce DNA from the donor bacteria into the recipient bacteria by infection
- bacteriophage infects the donor cell (host cell) = injects its DNA into the cell
- once inside the bacteriophages can follow either the lytic or lysogenic life cycle
- transducing phage with donor DNA infects the recipient cell
- homologous recombination occurs upon infection
lytic - lytic bacteriophages hijack the bacterium’s cell machinery to make more viral particles. this continues until the cell undergoes lysis and releases the bacteriophages. they can then infect the recipient cell
lysogenic - bacteriophage DNA is incorporated into the host’s genome at a specific site and form a protophage then remains dormant until triggered to enter the lytic cycle
What is the process of specialised transduction?
specialised transduction
- occurs when lysogenic donor bacterium enters the lytic cycle
- genes transferred depend on the location of the prophage on the chromosome
- prophage is improperly excised from the chromosome so adjacent donor bacterial genes
- excised DNA is packaged into a new viral package and lysis of the bacterial cell
- phage is released and the donor bacterial cell is infected
- donor genes can be inserted into the recipient chromosome or remain in the cytoplasm, depending on the nature of the bacteriophage
recombinant DNA has a genotype that is different to the donor and recipient = donor and bacterial
What are the different types of transduction?
specialised transduction
generalised transduction
abortive transduction
What is the process of generalised transduction?
generalised transduction
- occurs when the donor bacterium undergoes the lytic cycle
- mediates tranduction
- transferred donor DNA only/ no viral DNA
- bacteriophage infect the host cell and hijacks the cell machinery to make viral cell components
- viral enzymes hydrolyse the host cell DNA into small pieces
- when the bacteriophage is being assembled some of the donor cell DNA may be incorporated into the viral capsid
- donor DNA is not viral so does not replicate = bacteriophages with only donor cell DNA/ no viral DNA
- undergoes homologous recombination with the recipients DNA - has donor and recipient DNA
What is abortive transduction?
abortive transduction
- transient expression of donor genes
- donor genes are not recombined/integrated with the genome of the recipient bacterium
- donor DNA fragment does not replicate and only passes to one of the daughter cells
What is the difference between lytic and lysogenic cycle?
lytic
- phage attaches to the donor cell and injects its DNA
- phage hijacks the cell machinery and forms viral components = new phage DNA and proteins are synthesised
- cell lyses releasing new phages
lysogenic
- phage attaches to the donor cell and injects its DNA
- phage DNA integrates with the bacterium chromosome by recombination = forms protophage
- protophage reproduces normally until excised and triggered to enter the lytic cycle
What is a vector?
a vector is a living organism that transmits an infectious agent from an infected animal to a human or another animal
What is conjugation?
a sexual process
- transfers genetic material via direct contact between the donor and recipient bacterium
- encoded for by plasmids or transposons (segments of DNA that can move)
What is the requirements of conjugation?
donor bacterium must have F-plasmid/F-factor (fertility factor)
- they encode for the protein that makes the pilus (cytoplasmic bridge)
recipient bacterium must lack the F-plasmid
What is the process for conjugation?
F-plasmid codes for the formation of the pilus (protein)
pilus extends from the cell surface and attaches to the recipient bacterium = pulls them closer together, forms a mating pair
DNA is transferred across the pilus
- single DNA strand is replicated and transferred
- DNA strand replicates and forms a double stranded molecule which then forms the plasmid
Mating pair is broken at the end of conjugation
Homologous recombination of DNA
if the F-factor is transferred the cell can forms its own pilus and act as a donor
