Microbial genetics Flashcards
Resistance plasmids
- have resistance genes related to antibiotics and heavy metals that would kill ordinary bacteria.
- R genes
Resistance bacteria are ______ through ____
passed from bacterium to bacterium through conjugation
transfer of resistance plasmids occurs between
Occur between closely related genera
exaple of closely related genera
Escherichia Klebsiella Salmonella Serratia, Shigella and Yersinia
Vertical gene transfer
Gene transfer from mother to daughter cells
horizontal/lateral gene transfer
gene transfer between unrelated cells
Due to lateral gene transfer _____
organisms with similar genes may NOT have evolved from a common ancestor
Prokaryotic reproduction ______ requires _____
never requires gene exchange
Many euks reproduce ____ which requires ____
sexually, which requires meiosis and fusion of gametes
Prokaryotes reproduce ____ by _____
asexually by binary fission or budding
what makes a small amount of transferred DNA propagated?
if it integrates into a chrom or plasmid, or if it is a plasmid itself
propagated
replicated and handed down to progeny cells
euks are diploid or haploid
diploid
proks are diploid or haploid
haploid
because proks are haploid, what genes are expressed
recessive alleles or mutations are expressed in proks
genetic exchange among euks is done by
gamete fusion
Proks have 3 different mechanisms for gene exchange:
transformation
transduction
conjugation
Transformation
gene transfer by taking up soluble DNA from the environment
Conjugation, and what does it include?
Gene transfer that requires cell-cell contact
includes R plasmid, F plasmid, Hfr transfer
Transduction
- gene transfer by means of bacteriophages
- can be generalized or specialized
Griffith’s experiment, and the conclusion he found
- an experiment with pneumococcal infections in mice
- something from the dead S cells had “transformed” the R cells, making them smooth and virulent
Transformation requires _____ cells, which ______
Competent cells which can take up DNA from the environment
_______ transformations is ______
natural transformations is rare
natural transformations is observed in
S.Pneumoniae, B.Subtillis and H.influenzae
Artificial transformation
chemically competent cells
what are the 2 possible fates of linear DNA after entry in bacterial cell
- it can degrade in the cell cytoplasm
- it can undergo homologous recombination and becomes part of the chromosome
RECA
if homologous sequence is present, RECA catalyzes it and lets recombination occur
how does the Linear DNA go into chromosome
Through the use of nucleases
plasmid DNA can exist ___
on its own as long as it has its own origin of replication
generalized transduction
any of the host bacterium’s genes can be transferred
specialized transduction
only certain genes can be transferred
virulent phages
always replicate using the lytic cycle
temperate phages
can replicate using the lytic or the lysogenic cycle
lambda phages
can do lytic or lysogenic
all viruses can do ___ only some can do ____
lytic, lysogenic
Linear DNA must be _____
recombinated
only ____ cells can take in DNA, which is _____
confluent, random
an error in the assembly stage of phage replication causes
generalized transduction
an error in the prophage excision stage in the chromosome of phage replication causes
specialized transduction
lysogenic cycle exists
indefinetly (forever)
If specialized transduction occurs, _______ are always excised
same genes
gene exchange happens because of ______
mistakes done by bacterophages
Lederberg and Tatum discovered _____
conjugation
how was conjugation discovered?
Through mixing 2 different auxotrophs and recovered prototrophs
conjugation
requires cell-cell contact facilitated by sex pilli. Occurs in gram (-) bacteria
What gene does conjugation need
“tra” genes (transfer genes), this includes genes encoding proteins in sex pili
in gram (+) the mechanism for conjugation is ____
unknown
common types conjugation
F plasmic
Hfr
F’ plasmid
R plasmid
Virulence plasmids
rolling circle replication
A single strand of the F plasmid enters the F-cell
OriT
marks the region on F plasmid that enters the recipient cell first
- origin transfer
T/F A Hfr cell has the F plasmid integrated into the chrome
T
Hfr conjugation
Is genetically identical to F+ cell except its plasmid is not separate from the chromosome
the amount of DNA transferred in Hfr conjugation depends on ___
the amount of time the conj lasts
F+ cell and Hfr cell ….
can turn into or reverse back to each other
F’ conjugation is
Begins with Hfr cell, F plasmid excides itself, but it doesn’t do it percicley and takes some chromosomal genes with it, it is a mistake.
- this makes it F’
F’ plasmid
carries some chromosomal genes
genes on F’ plasmif are transferred to reci[ient F-cell during ____
conjugation
R-plasmids
responsible for the transfer of antibiotic resistance genes
- transferred like F-plasmids
What requires homologous recombination for the transferred genes to be inherited by progeny
Transformation, Hfr conj, generalized transduction
Mutation
any change in a cells DNA seq
small change in DNA
point mutations
Large change in DNA
deletions, insertions
mutations can be described by their ______
phenotypes
auxotrophic
defect in biosynthesis pathway so the mutant cell requires exogenous building blocks for growth
temperature sensitive
mutation that causes loss of a particular function at high or low temp
reversion (back mutation)
changes a mutated seq back to the original WT seq
Mutations can be induced by _____
mutagens
Transposon
mobile genetic seq that has genes for transposition
- often has R genes
- present in prok and euk
what can transpons do to DNA? what does this lead to?
they can randomly insert themselves into DNA, causing mutations and conferring antibiotic resistance
transposon mutagenesis
used to generate mutants for genetic studies
advantages of transposon mutagenesis
- mutations are marked by tn and antibiotic resist gene, the location of the must can be identified rapidly
disadvantaged of transposon mutagenesis
they only make insertion mutations, so mutations in essential genes may not be recovered
why would scientists do a genetic screen?
to discover genes involved in a process you’re interested in
how to do genetic screen
1) determine pheno of mut
2)mutinogize
3) let mut grow in permissive conditions
4) replica grow in restrictive conditions, this identifies mut with wanted pehno
CRISPR-cas
protects prok from repeat viral infections
