bacterial genetics Flashcards
how do the genetics differ from eukoryotes
bacteria have:
single, circular genome less than 5Mb
DNA not compartmentalized its just in they cyto
often contain plasmids (small fragments of dna) with the chromosome
Chromosome is condensed by supercoiling
when replicating: bacteria only have one origin of replication, and can replicate the genome more than once before the cell divides
when transcribing/translating: polycistronic an mRNA can become several different kinds of proteins
only 1 RNAP, and no introns or slicing
different sized ribosomes
how bacteria generate genetic diversity
clones with genetic modifications
replication errors- introduce mutations into the genes (drug resistance)
DNAp- misincorporates nucleotides and sdoesnt correct so a mutation happens (most mutations dont really confer a resistance)
horizontal gene transfer sending over genetic material
can happen between different species
helps outcompete and kill other organisms
largely responsible for the resistance (eg. Vancomyocin from VRE to VRSA)
horizontal exchange happens frequently
Gene exchange in bacteria
Exchangeable genetic elements: Plasmids, transposable genetic elements, pathogenicity islands
Plasmids
ss or ds DNA replicate independently, mostly circular
single (f plasmid) to multiple copies in cell
vary in size
can be transferred between bacteria by transformation, conjugation, and transduction
Transposable genetic elements
linear DNA segments that can be moved from one spot on the genome to another, disrupting gene in recipient
cant replicate on their own (need to be on plasmid or chromosome) to be passed down
they have inverted terminal repeats (ITR) at their ends contain transposase (enxyme that recognizes ITR and cuts DNA to transport that segment to another location)
different kinds: insertion sequences, composite transposons, TnA family (regulated by tnpT), mu bacteriophage
insertion sequence in bacterial genome that regulates virulent proteins
phase variation: where the insertion element is placed will determine if the gene will be turned on or off
insertion sequence undergoes site-specific inversion
spontaneuous switch between non-firmbriated and fimbrated forms
fimbriae promote attachment to urinary tract epithelial cell surface
genomic pathogenticity islands
large segment of bacterial genome carried on a plasmid or bacteriophage
they usually encode things that allow the bacteria to survive
cant replicate itself
ways that genetic excahange can be done:
transformation: dna taken up from the environment from a lysed cell (its the DNA not the proteins)
transduction: bacteriophage come out of cell and injects into a new cell
Conjugation: f plasmid (sex) two cells come together make a sex plus and the gene goes directly into the second cell
Bacterial transformation
uptake of DNA from the environment, occurs in gram+ and Gram-
natural or induced competent
Dna released from lysis
ds (on surface) is processed into ss DNA before being uptook
Conjugation
dNA passed one way from (D->R) required physical content occurs in both + and - requires complex set of genes DNA transferred thru mating bridge donor keeps one copy of DNA
Transduction
Bacteriophage kinda like virus
lytic- injecting phase
lysogenic- when encorporated into genome
virulence determinents that are carried on bacteriophage
cholera toxin (CTX phage) and shiga toxin
cholera toxin (CTX phage
filamentous bacteriophage that infects vibrio cholera and infects with a big gene that codes for cholera toxin (ctxAB)
comprimised of core element and a repetitive wequence
cholera toxin mechanism
a-5b toxin
b subunits bind to GM1 receptors in gut mucosa
the subunit is internalized and activates G proteins regulating adynalate cyclase
the toxin induces ATP->cAMP which ends up secreteing water and electrolytes
shiga toxin phage
larger and made by shigella dysenteriae and EHEC strains of e coli
induces sever diarrhea, hemmorrhagic colitis, and hemolytic-uremic syndrome (HUS)
big head, short tail
Genome is 48k bp that carries codes for shiga toxin (stxAB)
