Bacterial Genetics And Genetic Variation Flashcards
Prokaryotic vs eukaryotic genetics
Prokaryotes have a singular circular genome
Eukaryotes have a multiple linear chromosomes
P- generally haploid - one copy of each gene in bacterial genome - sometimes there are duplications of a gene
E- diploid
P- have extra chromosomal plasmids
P- coupled transcription and translation
E- separate transcription and translation
How do bacteria pass on their genetic information
Horizontal gene transfer
Vertical gene transfer
How does genetic variation occur in vertical gene transfer
By mutations
What is horizontal gene transfer
Sister to sister transfer
One bacteria passing genes to another without division
Why is genetic variation important in bacterial populations
Respond to selective pressure
Survive adverse environmental conditions
Exploit new environments
Genetic changes passed on through VGT
Spontaneous mutations
Single nucleotide polymorphism (SNPs)
Mutation rate is low ( slow process )
Types of HGT
Conjugation
Transduction
Transformation
What is conjugation
Conjugation is a process of genetic transfer in bacteria in which genetic material, usually in the form of a PLASMID, is transferred from one bacterial cell to another.
During conjugation, the donor bacterial cell forms
A PHYSICAL CONNECTION
, called a PILUS
, with the recipient cell.
The plasmid DNA is then replicated and transferred from the donor cell to the recipient cell through this pilus.
Conjugation allows bacteria to exchange genetic information, such as antibiotic resistance genes or genes encoding virulence factors, and can therefore contribute to the spread of antibiotic resistance and the pathogenicity of bacterial infections.
Conjugation can occur between bacteria of the same or different species, and it can occur under a variety of environmental conditions. It is a type of horizontal gene transfer, which is a mechanism by which genetic material is transferred between organisms that are not parent and offspring.
What is transduction
Transduction is a process of genetic transfer in bacteria that involves the transfer of genetic material from one bacterium to another via a
BACTERIOPHAGE, a virus that infects bacteria.
During transduction, a BACTERIPHAGE infects a bacterial cell and begins to replicate within the host cell. During the replication process, the bacteriophage may incorporate bacterial DNA into its own genome. When the bacteriophage then lyses (bursts) the bacterial cell, it releases new bacteriophage particles that can infect other bacterial cells.
If the bacteriophage contains bacterial DNA, it may be incorporated into the genome of the recipient bacterial cell, where it can be expressed and confer new traits to the cell. The transfer of genetic material via transduction can contribute to the spread of antibiotic resistance and the pathogenicity of bacterial infections.
Transduction can occur in two forms: generalized transduction and specialized transduction. Generalized transduction occurs when any segment of bacterial DNA can be transferred via a bacteriophage, while specialized transduction occurs when specific genes are transferred that are located adjacent to the site where the bacteriophage integrates into the bacterial genome.
What is transformation
Transformation is a process of genetic transfer in bacteria that involves the uptake and incorporation of
free DNA
from the environment into the bacterial genome.
During transformation, a bacterium takes up free DNA from the surrounding environment through its cell wall and plasma membrane. The DNA may come from another bacterium that has lysed or from the secretion of DNA by living bacteria. The DNA is then incorporated into the recipient bacterial genome, where it may be expressed and confer new traits to the cell.
Transformation is an important mechanism of horizontal gene transfer in bacteria that allows for the acquisition of new genetic material, such as antibiotic resistance genes, virulence factors, or metabolic pathways. Transformation can occur naturally in some bacteria, and it can also be induced experimentally by treating bacteria with chemicals or electrical pulses that make their cell walls more permeable to DNA.
The process of transformation has been extensively studied in the bacterium Streptococcus pneumoniae, which was the first bacterium in which transformation was demonstrated. Transformation has also been studied in other bacteria, including Haemophilus influenzae and Bacillus subtilis.
Properties of bacterial plasmids
Extra chromosomal pieces of DNA
Small circular molecules
Self replicating
Can be present in multiple copies
Key thing
They commonly encode genes required for virulence, including antibiotic resistance genes, toxin genes, genes that promote adherence to host cells
Process of conjugation
F plasmid is name given to plasmid that is going to be conjugated (plasmid that is being transferred)
Pilus come from the donor bacteria
Pilus connects donor bacteria to recipient bacteria
Plasmid is double stranded
Plasmid will be nicked by an enzyme and unravel and one strand will move into the recipient
DNA polymerase works in both cells to make the plasmid whole again
Process of transduction
Bacteriophage found in environment
They infect bacteria
Bacteriophage (virus) injects it’s DNA into the bacterial cell
( Bacteriophage protein coat and structure does not enter bacterial cell. )
The bacteriophage DNA will become circular
2 pathways could happen
Lysogenic life cycle or litic life cycle
Lytic life cycle
Phage DNA replicates straight away
Without integration into bacterial genome
These Phage DNA encode for proteins to make a new phage head
So brand new bacteriophages are being made
This causes the bacteria cell to lyse
And bacteriophages are released
Lysogenic life cycle
Bacteriophage DNA integrates into bacterial genome
This is called a prophage
Bacterium grows as a lysogen
So when bacteria divides its producing more lysogens
Something will eventually trigger the phage (which is now part of the lysogen) to enter the lytic cycle
(Possibly stress)
When this happens it leaves the bacterial genome, makes more bacteriophages and causes bacteria cell to lyse releasing them
—————————————-
Bacteriophage infects bacteria cell (we’ll call it the donor strain)
Bacteriophage DNA encodes proteins which start to make the bacteriophage heads
When bacteria is infected with bacteriophage bacterial DNA can be partially degraded
So occasionally when Bacteriophages are being made from the proteins that the original bacteriophage DNA encoded. Some of the partially degraded Bacteria DNA can be incorporated into the new bacteriophage
Therefore when the bacteria cell loses due to lots of bacteriophages
The bacteriophage with the donor strain bacterial DNA is released
This bacteriophage will go on to infect other bacterial cells and when the lysogenic phase of the lifecycle happens the donor strain bacteria DNA will be combined with the bacterial genome from a completely separate bacteria
What are pathogenicity islands
PAIs
Very large pieces of DNA 10kb-100kb
Often encode more than one virulence factor
Normally used to identify pathogenic and non pathogenic strains
Acquisition of PAI is a rapid evolutionary change
Non pathogen to pathogen in 1 step
Process of transformation
Sometimes bacterial cells will lyse
They will give up their DNA in this process (plasmid DNA in particular)
Living healthy bacteria are able to take up this DNA by transformation
Low efficiency
Can occur naturally or be induced artificially
Conditions must be favourable
Bacterial cells must be competent
