Prokaryotic Genetics in Nature Flashcards
how do prokaryotes reproduce
binary fission to produce geentically identical offspring
how are prokaryotes the masters of adaptation
-prokaryotes are not genetically stagnant
-they mutate, exchange genes etc
mutation
-a heritable change in the DNA sequence of a genome
-includes substituions mutations insertions deletions - any change
mutant
-organism whose genome carriea a mutation
wild type strain
-strain isolates from nature and or one being used as the parental strain i a genetic study
-the term wildtype can also be applied to a single
genotype
the complete genetic makeup of an organism
phenotype
an observale characteristic of an organism
-there can be many different sorts of phenotypes, metabolic virulence or morphology
mutants in prokaryotic genetics
-in prokaryotic genetics we seek to make mutations
-resulting mutant strains have a different genotype compared to the WT
-it is then common to test to see if the wild type mutant strains have different pehnotypes
natural mutation rate
10^-6–>10^-7 per 100bp per round of replication for prokaryotes
-average gene is around 100bp so each round of replication will introduce a mutation to a given gene in one of every 1-10million cells
-large enough numbers of bacteria in a population you will likely have some genetic diversity in each gene
horizontal gene transfer
-acquiring new genetic material from the environment plays a bugger role than mutations in prokaryotic evolution
3 major ways foreign DNA can enter a prokaryotic cell
-transformation, trasnduction, conjugation
once inside the cell DNA can
be degreaded or lost, replicate as a seperate entity like phages or plasmids
-be integrates into the chromosome through recombination or transpoition
transformation
-free floatinf DNA is incorportes into a recipeient cell and brings about genetic changge
-comes from variety of sources
-often comes from lysed cells within their environment
competent
-cell capable of taking up free DNA
-some bacteria and archaea are naturally comptent others are not
-competence is often tightly regulated
-many bacteria can be made competitent in the lab
how is DNA captured and cross the membrane in transformation
-DNA from environmnet is captured by pili which retract through outer membrane and cell wall
-one strand of DNA typically degraded and other strand passed through cytoplasmic membrane and into cell via multi protein competance system
transduction
-bacteriphage infections
-virus that infects bacterium
-virus DNA is packaged into virions which feature protein coats that protect DNA
-virion binds cell and injects DNA
Lytic and lysogenic pathway of transduction
-lytic - phage DNA replicated and new particles produced using host resources. Viruses then lyse host cell released to infect new cell
-lysogenic pathway - viral DNA integrated into host DNA-prophaage. Can be induced triggering the lytic cycle
temperate
can operate the lytic or lysogenic pathway
two types of transduction
-generalized
-specialized
generalized transduction
-during the lytic cycle some hsot cell DNA is accidentally packaged into a viral particle
-this DNa injected into new cell in place of phage DNA
specialized transduction
-when prophage is induced its DNA is excised from genome and packaged into phage particles
-sometimes some neighboring DNA is also packaged by mistake
-this DNA can then be injected into new cell by that phage particle
conjugation
-horizontal gene tranfer requires cell to cell contact
-typically conjugation is mediated by plasmids called conjugative plasmids, F plamid has served as a host model
-Donor cell used conjugative pilus to grab a reciepnt cell
-type 4 secretion system replicated and tranfers from donor to recipient
-reciepnet strain now carries the F plasmid and can serve as a donor
-this system can be used to transfer genomic DNA from one bacterium to another
how can foreign DNA be integrated into the host genome
-genetic recombination
-transposition
genetic recombination
-physical exchange of DNA between genetic elements- one important type is homologous recombination
homologous recombination
-important for DNA repair mechanism used to repair double strand breaks
-important for horizontal gene transfer
-In a nutshell, similar sequences can get shuffled around using this machiner
-foreign DNA with homology to a region of host chromosome can be insertd into genome in place of or in addition to the native DNA sequence
-important for genpme rearaangemnt such as deletions, duplication, inversion, of segments of DNA
transposable elemtns
mobile genetic elements found in almost all species
-contain transposase genes flanked by inverted repeats
transposase enzymes are able to
-recognize inverted repeates of DNA sequences
-cleave that DNA to free transpoable element
-cleave another dna (e.g chromosmal DNA)
-insert the transposable elemnt into that DNA
-this process is called transposition
conservative vs replicative mechanism
-conservative - move from one place to another
-replicative - transposon remains and a copy is produced and inserted elsewehre
transpoable elements figure
evolution via horizontal gene transfer
-alot of acquired dna is lost as its not evolutionary useful
-genes that provide a selective advantage will be maintained and can outcompete parental strains that lack this new DNA
-mricobial genomes contain a greta deal of horizontally acquired DNA
-can tell horizontally acuqired DNA by %GC content
-has huge impacts on infectious disease factors like virulence mechanisma nd AMR
