Bacterial Genetics Flashcards
auxotroph
mutant that requires a growth factor
prototroph
does not require a growth factor
silent/synonymous mutation
change that generates codon that translates into the same amino acid as original
missense mutation
altered codon codes for a different amino acid (often this will cause the mutant cells to grow slowly)
nonsense mutation
early stop UGA, UAA, UAG
null/knockout mutation
totally inactivates gene
transposon
DNA that can jump into the host genome, may enter cell through a plasmid - can move into host cell genome and jump in at different sites may be replicated then leave again as plasmid. Often makes genes dysfunctional
plasmids
can exist in bacteria/archaea/eukarya/yeasts
circular double stranded DNA molecules
Have origin of replication (can be passed on through replication)
generally do not encode useful info
narrow host range - normally very specific
mobilizable plasmids
origin of transfer but lack other genetic info for transfer - they can transfer when conjugative plasmid is present
conjugative plasmids
carry all the genetic info needed for transfer
Resistance or R plasmids
encode resistance to antimicrobial chemicals (including antibiotics)
What are the components of the the simplest transposon? What is the simplest transposon?
insertion sequence (IS) transposon is the simplest only incodes transposase gene (which makes enzyme for transposition) and inverted repeats
non-homologous recombination
DNA recombination that does not require extensive nucleotide sequence similarity in the streches that recombine
genomic island
large segment of DNA in cell’s genome that originated in different species
pathogenicity islands
genomic islands that contain genes that increase the disease-causing abilities of the bacterium
core genome
conserved genes of the species
mobile genome
very different genes that make up certain strains, can move from one DNA molecule to another
what are some mobile genetic elements
phage DNA, plasmids, transposons, genomic islands
direct selection
used to isolate mutants that can survive conditions that their parents can’t
indirect selection
used to isolate auxotrophic mutant from prototrophic parent strain
- difficult to do b/c both grow on medium so
- replica plating is used
what can be transfered from one cell to another by conjugation?
plasmid DNA
chromosomal DNA
which kinds of mutations do chemical mutagens cause?
frameshift and base substitutions
mutagens that modify nucleobases change what properties?
base pairing
what chemicals did you learn about that add alkyl onto nucelobases and create mutations?
alkylating agents
Base analogs
structurally resemble nucleobases but have different hydrogen bonding properites but can be mistaken as nucleotides and then put into DNA creating mutation
chemical mutagens that squeeze between base pairs and induce frameshift mutations are called
intercalating agents
which DNA segments increase the rate of mutations by inserting themselves into DNA and inactivating them?
Transposon can move form different sites on host genome, into host genome, out of host genome to plasmid and this can create mutations
what are the mutagenic types of radiation?
ultraviolet light - can cause thymine dimers to form
X-rays - cause breaks in DNA (double and single stranded)
reversion
when mutation changes back to original non-mutated state (occurs spontaneously and at low frequencies)
why would you give two antimicrobial medications?
because the rate of mutation is very low, so the likelihood that the a cell simultaneously, spontaneously becomes resistant to both is very low
base substitution
most common type of mutation, during DNA synthesis when an incorrect nucleotide is incorporated
point mutation
if only one base pair is changed
base substitutions increase when…?
ROS (reactive oxygen species) are around in aerobic environments because the oxidize guanine which leads to more mistakes
what is naked DNA
free floating DNA
DNase
enzyme that degrades DNA - can only degrade free floating when free floating
what is the specific physiological state that allows the cells to take up DNA
competent state - some cells only reach competent state when recourses are low or cell density gets low (not very many bacterial cells)
how many strands of donor DNA integrate into a recipient chromosome during transformation?
one
