Bacterial Genetics Flashcards
Why do people study bacterial genetics
Simple organisms
Haploid which means no masked mutations
Fast replication
Bacteria follow the Darwinian principle- what is this
Beneficial mutations which are random occur in populations then are passed down to progeny
Bacterial transformation is a way of horizontal gene transfer- explain the process
Cell free dna which is double stranded is turned into 1 stranded
- via hydrolysis of one strand
This then enters a host cell and is crossed over in a HOMOLOGOUS REGION with the chromosome
When it replicates ONLY 1 WILL BE RECOMBINANT WITH THE TRANSFERRED GENE
What is homologous recombination?
When the strands of DNA are already similar or same in bases so can mix (Eg in transformation)
What is bacterial conjugation
Cell to cell gene transfer (mating)
What type of plasmids are needed to allow conjugation gene transfer
Conjugative / fertility plasmids
How do the cells in conjugation meet
Sex pillus which contracts
What is it called when the bacterial chromosome is transferred in conjugation
High frequency recombination (HFr)
In which cases are non conjugative plasmids transferred
If they have mobility genes
How does a F+ cell turn a F- cell into F+ (getting a f factor)
When the cells cytoplasms are brought together 1 5’ strand from f factor is transferred
This is replaced in original cell by replication.
The single strand is then replicated to have a full plasmid f factor in the new cell.
What kind of strand is transferred to cells in conjugation
5’ strand
How does HFr cell get turned into a F- cell?
An F factor is incorporated in the chromosome of original cell first
VIA CROSSING OVER.
The F factor 5’ strand then moves into the other cell and strand is replicated.
The f factor is incomplete however (not full plasmid/genes)
Crossing over occurs in the new cells chromosome and the F factor.
The linear chromosome is then degraded and the cell is left with recombinant alleles in chromosome.
Why doesn’t the HFr cell able to make a full F+ cell?
The F factor is incomplete when it is transferred meaning not all genes are present.
What is an F’ cell in conjugation
When the F factor is on seperate strand to chromosome
How does HFr cell make a F’ cell using cross over conjugation
The chromosome with the F factor incorporated crosses over itself.
This separates the f factor and chromosome
The f factor contains some genes eg lac gene
This then is transferred to an F- cell at 5’ f strand. And is replicated to have a full f factor
This produces 2 F’ cells with copies of lac gene
What is transduction
Gene transfer by a bacteriophage (virus)
Explain the lytic cycle of transduction with phages
Phages will inject its dna into a host cell
Enzymes then degrade the host cells dna into fragments
The phages dna will replicate
The dna fragments are assembled to transcribe for phage proteins
The proteins are assembled into new phages
Lysis occurs (new phages are released)
THERE IS GENE TRANSFER BECAUSE SOME DNA FROM HOST CELL IS INCORPORATED IN THE PHAGES WHICH NOW INJECT NEW CELLS
= TRANSDUCTANTS
Explain the lysogenic cycle of transduction
Phage dna when injected can be integrated into the host cell chromosome
This produces a PROPHAGE
The prophage is replicated to new cells
The prophage can seperate from the chromosome eventually and go into the lytic cycle to be used to make new phages
What is the phage dna called when integrated with chromosome in lysogenic cycle?
PROPHAGE
Chromosomes are mostly circular on bacteria, what is the site called where replication begins
The origin of replication (oric)
When oric initiated replication, what directions is dna replicated
Both directions
What are replication forks
The region where the new strand is forming in replication of dna
What is the point called where replication of circular chromosomes stop
Termination point of replication
