Download Viruses and bacteria

Viruses and bacteria
Bacteria = prokaryotes = Kingdom Monera
No nucleus
Circular DNA (nucleoid)
Reproduce by binary fission ~ 20 minutes (ideal)
Rate of mutation high ~ 2000 mutations/day
Genetic recombination via sexual reproduction (conjugation)
Adds to diversity
May have plasmids Circular DNA NOT in bacterial DNA
Plasmids
Not part of bacterial chromosome
Can replicate independently
Usually replicate at same time as chromosome (nucleoid)
Episome = if can replicate independently
Some viruses qualify as episomes (lytic cycle)
BUT plasmids have no extracellular stage
Plasmids usually benefit host
Not required for normal survival
Can be advantageous in changing environment
Bacterial recombination and
transposition
Causes new bacterial strains
Bacterial DNA recombines changing genetic make up
Transformation
Transduction
Conjugation
Transposons
Transformation
Bacteria ‘uptakes’ DNA from surrounding environment
Hershey – Chase experiments in search for genetic material
Recently : increase in Ca++ concentration
stimulates uptake of DNA (competent)
Preview lab 6
Transduction
Phages transfer DNA from host to host
Generalized transduction
Bacteria ‘infected’ with viral DNA
As virus replicates, bacterial DNA in viral capsid
Viral capsid with bacterial DNA ‘infects’ new host bacteria
DNA becomes
part of new
host DNA
Specialized transduction
Prophage joins with host DNA
When prophage exits
bacterial DNA,
it takes some of bacterial DNA
New phage in capsid
breaks out of host
New phage ‘infects’ new host
and becomes part of
new host DNA
New host with new
bacterial DNA
Conjugation
Sexual reproduction
Sex pili form pili bridge to DNA recipient (‘female’)
Requires F plasmid (fertility plasmid)
F+ bacteria transfers F plasmid to F- bacteria creating F+ bacteria
OR
F+ becomes Hfr (F plasmid in host DNA)
F plasmid WITH host DNA sent to F- bacteria
Creates new F+ bacteria with new DNA
R plasmids (for antibiotic resistance)
can be passed along via conjugation
Transposition
Transposons = pieces of DNA that can from one location to another
“jumping genes”
Most common transposons = insertion sequences
Code for transposase
Enzyme needed for transposition
Transposase locates inverted repeats
Cuts DNA to remove insertion sequence
Inverted repeat ‘glued’ back together
Insertion of transposonase cuts target DNA
Inserts transposon Matching DNA ‘replaced’
Transposons increase potential genetic variation
Help inject R plasmids