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Bacterial Genetics, Know the difference! - Coggle Diagram
Bacterial Genetics
Elements of the bacterial genome
chromosome
Most bacteria are haploid (one copy of the chromosome), so mutations are common
plasmids
bacteriophages
insertion sequences
Move DNA to other places within one cell
Transposase recognizes inverted repeats and moves the IS
Cut and paste
transposons
Move DNA to other places within one cell
Gene encoding an observable function flanked by two copies of an insertion sequence -
can especially transfer antibiotic resistance
Mutations
can change a bacterial gene so that the protein is no longer affected by an antibiotic, yet still retains its function
Completely new genes are not constructed by a single point mutation
Mechanisms of genetic exchange
transformation - uptake of naked DNA
The recipient cell must be competent for uptake of DNA
natural competence
artificial competence (lab only)
Only certain bacteria are naturally transformable
transduction - bacteriophage as vectors
Bacteriophage (phage) = virus of bacteria.
lytic - always lyse (kill) host bacterial cell
temperate - can stably infect and coexist within bacterial cell (lysogeny) until a lytic phase is induced or just lyse immediatley
lysogeny
phage genome = prophage
bacterial cell = lysogen
lysogenic conversion - phage encodes observable function
Specialized Transduction Example
prophage integrates into the bacterial genome
prophage may drag along a piece of the bacterial genome into the next integration site
That sequence is added into the next bacteria's genome, changing their genome
Generalized transduction
When a phage lyses the host bacterial cell, it normally packages phage genome into the capsid
Sometimes the capsid is accidentally filled with random pieces of bacterial genome
When the capsid injects to a new cell, the new genes can recombine into the recipient's genome and cause change
Virulence and antibiotic resistance genes can be moved by generalized transduction
conjugation - plasmids moved by cell-cell contact
conjugative
plasmid can move itself from donor cell to recipient cell
mobilizable
plasmid can not move itself, but can be moved
non-transmissible
can't move by conjugation
Mechanism
Pilus forms
cell-cell contact
copying plasmid DNA and transfer of copy into recipient cell
more common method of sharing antibiotic resistance genes than phages - can move multiple at once
Phase variation and Antigenic variation
Phase Variation
Binary switch - something goes from on to off, or A to B
Caused by a flipping of DNA
Antigenic variation
Change in sequence with multiple possible outcomes
Cassette model
silent copies of the gene of interest are recombined to a site where the cassettes (genes) can be expressed
Know the difference!
