Lec8 Bacterial Genetics Flashcards
What are the genetic characteristics of prokaryotes?
- haploid genome
- genes arranged in operons
- no splicing of mRNA
- mutations/selections make population change rapidly
What are plasmids?
- self-replicating DNA units with accessory genes
- contain many genes required for virulence
- can also contain genes for resistance
What are 4 mech of mutation
- replacement
- deletion
- insertion
- inversion
What are mutation replacements? how frequent?
- spontaneous freq. 10^-6
- operon struct so stop/start mut have polar effects
What type of mutation is the one in RNA-pol that gives rifampin resistance?
point mutation
what type of mut causes beta-lactmase change in substrate specificity?
point mutation
What time of mutation causes flagellar synthesis to evade immune response?
framseshift as microdeletions
what are 3 types of genetic exchange?
- transformation
- conjugation
- transduction
What is transformation?
- gene transfer from donor
- efficiency affected by DNA size and state
- it is sensitive to nuclease [DNAse]
- works for bacillus, haemophilus, neisseria, streptococcus recipients
- double strand DNA received by donor, one strand enters cell and other degraded, get recombination by double crossing over into recepient plasmid
- after recplication get 1 transformant and 1 nontransformant
what is conjugation?
- dna transferred from bacteria donor F+ cell to recipient F- cell by direct contact
- transfer mediated by pilus [tube-like struct] between cells through which plasma DNA passes
- DNA transfer unidirectional
- both donor and recipient end up with a full copy of the plasmid
- conjugation also involves transfer of plasmids that carry antibiotic resistance
- works in e coli, gram negatives
what is transduction?
does not require physical contact of cells
DNAse resistant
happens via lytic or lysogenic cycle
DNA transferred from one bacterium to another by a bacteriophage [virus]
What are bacteriophages?
viruses that infect and replicate within bacteria
What is the lytic cycle
- virus enters plasma membrane and releases genetic material into cell
- make huge amounts of virus
- kill cell during replication
what is the lysogenic cycle?
- no progeny particles produced
- infected bacterium survives
- phage DNA integrates into bacterial chromosomes
- phage DNA transmitted to each bacterial progeny when cell divides
- virus integrates and is latent
What do you call phage that is capable of lysogenic cycle?
temperate
Which phage species can undergo lytic cycle? what do you call phages capable of lytic cycle but not lysogenic?
all phages can undergo lytic
if can only do lytic –> virulen
mech of lytic infection causing transduction
in lytic infection: transducing phage accidentally pakacages piece of bacterial chromosome into a virus particle instead of its own viral dna, carries the bacterial DNA then delivers it to recipient when it is trying to infect in, injected bacterial DNA inserted into recipient chromosome by homologous recombination
How much bacterial DNA does a typical P1 bacteriophage contain?
50 genes [80 kb bacterial DNA]
What is relationship of relative location of two genes and probability of simultaneous conduction?
- if two genes closer together, greater frequency of cotransduction
What are two well known examples of bacteria whose toxins that are often transmitted from bacteriophages?
- corynebacterium diptheriae
- vibrio cholerae
What are transposable elements?
DNA seq that can jump from one position to another or one DNA molec to another
What are IS elements?
- insertion sequences
- 1-3 kB in length, encode transposase protein required for transposition
What is a transposon?
- transposable element that contains transposase as well as one or more genes
- can insert into plasmids which can then be transferred via conjugation to recipient cells
What is an integron?
- DNA elements that encode site-specific recombinase
- have recognition region that allows other seq. with similar recognition regions to recombinate in
- elements that it acquires are called cassettes
What are mechs of linear transmission of genetic variations?
- point mutations, DNA rearrangement
What are mechs of horizontal transmission of genetic variation?
- transformation
- conjugation
- transduction
What are 3 paths that could happen to DNA that comes into a bacterial cell?
- destruction [by nucleases or inherent instability]
- stabilization without replicative possibilities [ie circularization]
- integration by recombination
What are 3 processes of integration?
- homologous recombination [RecA dependent]
- site specific recombination [phage mediated and through transposable elem]
- illegitimate recombination [nonhomologous]
What makes VRSA resistant?
carry resistance on specific mobile genetic element
What is cause of reduced daptomycin resistance in VISA?
mutation in rpoC [beta subunit of RNA ploymerase] and mutations in yyc gene cluser
What makes VISA resistant?
- multiple mutation
35 mut at 31 loci causes differential gene expression of 224 genes
