Bacterial Genetics (8) Lecture Flashcards
Transformation
transforming a recipient cell into something else
two strains that can’t grow, put them together and if they transform maybe they will be able to grow
Recombinants
result of transformation, have properties of original strains
Griffiths Experiments
one strain killed mouse and the other did not
the lethal strain when heated did not kill mouse
dead lethal strain + non lethal strain = dead mouse
why? something was transforming and it was DNA
Horizontal Gene Transfer
transfer of traits between cells
What are the types of horizontal gene transfer?
- Transduction (through phage)
- Transformation (naked DNA)
- Conjugation (fertility/mating of two cells)
What must happen to the DNA once inside the cell?
the foreign DNA must integrate in to the hosts genome or be able to replicate independently which would mean it would have to be a replicon (has a origin of replication)
What is the most common way of integration?
homologous recombination
gene on one strand has mutation and is switched out with non mutant gene - then the non mutant floats around and is degraded eventually
What is the most common way for antibiotic resistance to happen?
horizontal gene transfer (transduction/transformation/ especially CONJUGATION)
DNA mediated Transformation
uptake of naked DNA (takes up linear free floating DNA and incorporates into host chromosome)
Competence
induction of gene to code products that lets bacterium take up DNA from outside and integrate it into the chromosome or “ability to take up DNA”
Are all species competent
no, only certain species are naturally competent
What is the result of DNA mediated Transformation?
replication will generate one wild type and then one recombinant
DNase
enzyme that degrades DNA (so it would degrade naked DNA but not be able to get through cytoplasm)
Which process of Horizontal Gene Transfer is sensitive to DNase?
Transformation - b/c takes up naked DNA
Transduction
DNA is transferred via bacteriophage
- generally this is an error in phage replication cycle
two types: generalized and specialized
generalized vs. specialized transduction
lytic or temperate phage = generalized (will produce transduction particles possibly aka phages that messed up and took host chromosome before being released)
temperate phages only = specialized (incorrect inexcision) - meaning that part of the phage DNA and part of the host DNA packaged making a defective phage
Transducting particles
when original chromosomal DNA from the host is accidentally packaged into a phage making it a defective phage
- you could add a transducting particle to new cell to get a new trait
Defective phage
lacks full phage chromosome can go into new cell and transduce new cell
Conjugation
mating / probably responsible for most antibiotic resistance
requires cell to cell contact
involves a CONJUGATIVE PLASMID
- The F plasmid (fertility plasmid) serves as a model
- plasmid in-codes machinery for its own transfer
- F+ is the donor
- F- is the recipient
- F is the plasmid
What are the two types of donors (in conjugation) we learned
F+ (transfers plasmid)
Hfr (transfers chromosomal DNA)
What does F+ use to attach to F- ?
pilus
What does F+ added to F- make?
two F+ cells
add one F+ to a bunch of F- and eventually all of them will be F+
both have copy of donor plasmid
R-plasmids
resistance plasmids
encode resistance to antibodies/antibiotics
they are also conjugation
the plasmid has the origin of replication and the origin of transfer
What is the significance of Hfr strains?
Hfr = high frequency recombination
used to map gene order for circular chromsomes
you can time the amount of conjugation then see what genes made it over in that time in order to map
How is the Hfr strain formed?
F plasmid occasionally integrates into the chromosome creating one large chromosome then the F plasmid still preforms conjugation with the recipient but now drags some of the donors chromosome attached to the F plasmid over
cells inevitably separate before entire chromosome its transferred - you could separate them by shaking a tube
