Genetic Exchange Flashcards
What is Transformation?
The uptake of DNA from a medium and its incorporation into a host chromosome!!
In nature, what is the source of transformation? what is it sensitive too?
In nature, usually lysed cells provide free floating DNA molecules for transformation
this makes them sensitive to DNase which chews up naked DNA
What does it mean for a cell to need competence for transformation to occur.
Cells need to reach a certain level of competence which is based on growth before they are able to perform transformation
If there is enough homologues in the host DNA what occurs to the up taken DNA?
Recombination occurs and DNA is incorporated into the genome
What occurs of the host cell does not like the up taken DNA?
Degradation
What bacteria is well studied for competence and transformation?
Streptococcus Pneumoniae
it is gram positive!!!
Explain how S. Pneumoniae initiates transformation
1) during exponential GROWTH the cell secretes competence factor (CF)
2) CF binds to cell surface which signals translation of many new proteins
what is the major protein synthesized after CF binding that is responsible for transformation ?
Autolysin
explain how DNA enters the cell and the 2 major proteins involved (start with CF binding) (6)
- CF binds and causes autolysin translation
- Autolysin chews up some of the Peptidoglycan layer and exposes a DNA binding protein and a nuclease on cell surface.
- DNA binds to binding protein in double strand form
- nuclease cuts off (hydrolyzes) one of the strands of DNA
- other strand is facilitated into the cell
- may integrate may degrade
what is a transformant?
An up taken DNA that enters genome of host thereby altering its genetic makeup
true or false, Any DNA molecule can bind to the DNA binding protein in Competent factor transformation (human, pig, bird, etc)
TRUE, transformation allows the binding of any species DNA
What are the 4 proteins associated with transformation in GRAM POSITIVE bacteria?
binding protein: a pilus called ComEA
nuclease: called EndA
channel: called ComEC
chaperone: ComFA
What bacteria is well studied for No competence factors and transformation?
Gram negative Haemophilus influenzae
How do we know when gram positive cells are competent?
they release CF’s
How do we know when gram negatives are competent?
we don’t know for sure.
Explain how transformation works in gram negative cells
- gram negative bacteria becomes competent during growth
- Double stranded DNA enters OM and then enters PM as Single stranded DNA
- Only binds DNA of close relatives!
why do gram negative cells e.g Haemophilus influenzae only bind DNA of close relatives?
this ensures the homology of the up taken DNA is similar to the host. This increases the chances of recombination occuring
For gram negative bacteria (Haemophilus influenzae) what is one requirement for DNA to be up taken.
It must contain a specific 11 base pair sequence
What creates the pore in the gram negative transformation? what is its equivalent in the gram positive transformation?
PilQ creates pore in negative
ComEC creates pore in positive
Explain Artificial transformation
Treat non competent cells such as E. Coli with cold CaCl2 to mimic artificial competent
True or false, in artificial transformation linear DNA is easier to up take than plasmids
false, Plasmids are easier to up take
Explain Electroporation (3 steps)
1) make cells electrically competent by washing them in cold distilled water
2) now competent cells are mixed with naked DNA and exposed to high voltage pulses
3) pulses open up small, resealable holes for DNA to enter through
Very universal for non-competent DNA
What is transduction? what is the general process?
Genetic info can be transferred from one bacteria to another via a bacteriophage.
During phage infection bacterial DNA is accidentally packaged into a phage head. This phage infects new bacterium and supplies New DNA of last infected cell
What are the two types of bacteriophages? how do each reproduce?
Virulent phages: reproduce via the lytic cycle
temperate phages: reproduce via lysogenic cycle
