Bacterial Genetics Flashcards
Many microbial genomes cause…
Severe disease like sepsis
What is the bacterial genome and what do they not often contain
A chromosome- bacteria have 1, some have 2 chromosomes- some have linear chromosomes
-contain very little junk DNA meaning they don’t often have histones as they have little function
Genes in bacterial genomes with related functions often linked together in…
Operons
Bacteria that cause disease have a ________ genome, this mean that’s
-Flexible
-they acquire new genes that allow them to evolve and cause disease or to acquire antibiotic resistance
Name the structures of a bacterial cell that a flexible gene pool contains
Genomic islands
Genomic islets
Phases
Plasmids
Integrons
Transposons
What is an Operon
a unit made up of linked genes which is thought to regulate other genes responsible for protein synthesis.
Name the compounds that make up a lactose operon
LacZ = B-galactosidase
(Lactose – glucose + galactose)
LacY = Lactose permease
LacA= Lactose acetylase
Which molecules does the lactose operon need to work
Lactose repressor
RNA polymerase
Lactose
Describe what happens when we put bacteria into solution with no lactose operon present vs when its put into lactose solution
- Lactose operon absent: Lactose repressor binds to operator site and lactose genes are repressed; enzyme activity inhibited
- When present; binds to repressor which causes a structural change in repressor; starts binding to operator site in promoter, RNA polymerase combine and you get transcription of enzyme and lactose is broken down
What is derepression
repression is a mechanism often used to decrease or inhibit the expression of a gene. Removal of repression is called derepression
Iron is essential for _________ growth
Bacterial
What is activation mechanism controlled by?
Temperature
What is a mutation
-types
Change in base sequence of DNA
-base substitutions
-frame shift
-deletions
-insertions
-inversion
-transposons (cause mutation in bacterial genomes)
Causes of mutations
Spontaneous - replication errors; naturally
Mutagens; artificially
– Chemicals - eg. nitrosoguanidine
– Radiation -eg. UV radiation
– Insertion of transposon or bacteriophage
Effects of mutations
No effect on phenotype
– Normal protein or protein with minor change in activity
produced
Pathogenic bacteria
– Prolonged growth in vitro
• avirulent (attenuated) mutants arise and predominate
– Repeated passage (infection) through target species
• Strains with increased virulence may arise
Antibiotic resistance against fluoroquinolones
-single point mutation within gyrA subunit of DNA gyrose confers resistance
What are fluoroquinolones
-Bactericidal (kill bacteria) antiobitics
-inhibits DNA gyrase and topoisomerase which are found in bacteria; works by supercoiling the DNA in bacteria
Transposons
-what are they
-what do they contain
-function
-A jumping gene; jumps from genome to genome either in same piece of DNA or from one piece to another
-essentially a mobile genetic element
-found i prokaryotes and eukaryotes
-has a transposase gene which allows it to move
-has inverted repeats (IR) at both ends which are recognised to allow it to insert into pieces of DNA
-can reverse or create mutations which allows for antibiotic resistance etc.
Composite Transposon Tn10
-what makes it different from normal transposon
- a more complex transposon
-has insertion element at both ends
-contains a resistance gene
Site of insertion of transposons is ransomed or non random?
Random!
What does insertion of a transposon cause
Disruption of gene; causes polar mutations in operon
2 types of transposons
Insertion element (IS)- simplest
Composite transposons- complex
Difference between simple IS transposons and complex composite transposons
IS- transposition is only phenotype
Composite- carries antibiotic resistance genes. and virulence factor genes
Name the 2 types of mechanisms of transposition (transposon)
Conservative transposition
Replicative transposition
Where do enterococci bacteria live?
In the gut
Describe the mechanisms of transposition (transposons)
On anki cards bacteria
Plasmids characteristics
-Replicate independently from host genome
-double stranded DNA
-Encode functions that may give the bacteria/host an advantage
-may carry virulence factors and carry antibiotic resistance genes
How do plasmids acquire antibiotic resistance genes
Via transposons; they jump into plasmids and plasmids are shared around between different bacteria
Plasmids have different ranges of:
Copy number
Conjugation
Host range
-describe what each of these are referring to
Copy number- the number of plasmids in bacteria; the higher the number of plasmids with resistance genes they higher the antibiotic resistance is in the bacteria
Conjugation; self transfer via direct contact
Host range- some plasmids have lots of different bacteria they can get into and some have narrow host ranges
What is colistin and how is it spread
Highly toxic drug that fell out of use due to its toxicity, however now that we are running out of drugs that bacteria are not resistant to, it is coming back
Spread by conjugation (plasmid swapped between bacteria)
What are bacteriophages
How do they work
-Bacterial viruses
-work by binding to a bacteria, take over protein synthesis and machinery of bacteria, replicate their nucleic acid and produce new viruses
Name the life cycles of bacteriophages
Lytic cycle
Lysogenic cycle
Describe in simple words what happens in the lytic cycle and lysogenic cycle of bacteriophages
Lytic; Lyse the bacteria
Lysogenic; integrate into bacterial chromosome; hitch a ride on the bacterial genome
Describe the process of lytic cycle of bacteriophages
-Bacteriophage nucleic acid gets into bacteria
-bacteria replicated with nucleic acid as well
-new viruses produced
-bacteria lysed
-cycle starts again
What can bacteriophages be used as
-bacteriophages are specific or non specific?
Antibacterial treatment; topical therapy eg skin infection
-specific
Describe the process of lysogenic cycle of bacteriophages
- Nucleic acid of phage integrated and injected into bacterial cell; it circularises (looks like a plasmid)
- Homologous recombination betweeen sequences on bacterial DNA and viral nucleic acids and its integrated
- Replicated as bacterial grow
Once bacteria gets to a stage that it can’t grow; it lyses and kills the bacteria and goes on to infect new bacteria
Bacterial pathogens have pathogenicity islands. What are they? What’s interestingly different about them and what does this tell us about them?
Blocks of DNA inserted into chromosome containing virulence genes/ virulence factors
Have a different C+G sequence content of DNA than rest of chromosome (general lower) this tells us block of genes has come from another bacterium.
Name the 2 important pathogenicity islands contained in salmonella
SPI & SPII
List the mechanisms by which bacteria transfer genes
-why are they important?
-Unidirectional, donor to recipient
-Transformation
-Transduction
-Conjugation
Important because;
a. move antibiotic resistance genes among bacteria
b. move virulence genes among bacteria
c. change the antigenic make-up to avoid immunity
Transformation mechanism of transfer of genes between bacteria
-What is it
-2 types
-Uptake of naked DNA; bacteria taking up DNA of lysed bacteria in the area, allowing it to take useful traits for itself to allow it to survive; usually chromosomal fragments
-can be natural or artificial (artificially making mutants to study them)
Transduction mechanism of transfer of genes between bacteria
-what is it
-2 process types
-Transfer of DNA from one bacterium to another via a bacteriophage
-generalised transduction & specialised transduction; both utilise the bacteriophage life cycles (lytic & lysogenic)
Describe the generalised & specialised transduction processes
On anki cards
Conjugation mechanism of gene transfer between bacteria
-what is it
-how does it work
-what is it important for
-what can it also do
-bacterial sex
-sex pilus on conjugation plasmid contacts another bacterium usually of same species and transfers the conjugate plasmid
-important for dissemination/spread of antibiotic resistance genes and mobilisation of non conjugative plasmids
-transfer bits of chromosomal DNA
What is a conjugative plasmid (also known as F, fertility factor)
A plasmid that has all the genes required for bacterial exchange; includes the sex pilus
What is recombination
2 types and their result
Crossover events that occur when new DNA is acquired by the bacteria
-single cross over (result-> integration of plasmid into chromosome) and double cross over (result-> exchange of homologous regions)
Salmonella
Typhimurium DT104
Mainly cattle infections and transmitted to man via food
Chromosomally encoded resistance to ampicillin, chloramphenicol, streptomycin/ spectinomycin, sulfonamides and tetracyclines (ACSSpSuT) – genes acquired via plasmid integration into chromosome
-Also contains a 6.8-kb plasmid coded for resistance to sulphonamides and trimethoprim
-Chromosomal mutations to Ciprofloxacin
