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Intro to Microbial GeneticsGenetics
An Introduction to Microbial Genetics
Bacteria Reproduce Asexually via
Can this generate n ti di r it ?!?genetic diversity?!?
But, Bacteria still undergo GENETIC RECOMBINATION (combining DNA from two
individuals into the genome of a single individual)
Genetic Recombination in bacteria occurs through three distinct processes:
1.TRANSFORMATION-Def: The uptake of naked, foreign DNA from the
The foreign DNA may be incorporated into the bacterial chromosome.
Some bacterial cells have specialized surface Some bacterial cells have specialized surface proteins for the uptake of DNA.
Def: Phage (bacterial viruses)
carry bacterial genes from one host
cell to another.
Generalized Transduction occurs when the phage accidentally transfers random bacterial
genes instead of its own.
Specialized Transduction occurs when the phage takes a small adjacent region of the
bacterial DNA with it.
Def: The direct transfer of genetic
material between two bacterial cells that
Transfer is one-way, with the DNA donor (or male) attaching to the DNA recipient (female) with a sex pilus.
The ability to form sex pili and donate DNA results from the presence of an F factor.
General notes about PLASMIDS
Plasmids are small, circular, self-replicating DNA molecules separate from the bacterial chromosomes.
Some plasmids, like the F plasmids, can reversibly incorporate into the cells chromosome (an episome).
R PLASMIDSR plasmids contain genes conferring
resistance to antibiotics.
R plasmids, like F plasmids, have
genes that encode sex pili and enable
transfer from one cell to another.
Many R plasmids carry multiple
antibiotic resistance genes.
R Plasmids acquire multiple resistance genes through TRANSPOSONs.
Transposon: a piece of DNA that can move from one location to another in a cells genome.
Transposase catalyzes the movement of the transposon from one location to another
Composite Transposons include extra genes sandwiched between two insertion sequences.
Composite transposons can add a gene conferring antibiotic resistance to a plasmid already carrying genes
for resistance. In an environment high in antibiotics, natural selection will favor multi-drug resistant bacterial
cope with cope with environmental fluctuation at several levels:
Regulation of Gene Expression occurs through OPERONS.
OPERONS utilize a segment of DNA called an OPERATOR. The operator controls the access of
RNA polymerase to the genes.
OPERATORS function as switches to turn transcription ON or OFF.
Operators are ON unless a specific REPRESSOR PROTEIN is bound to it.
This operon, the trp operon is an example of a REPRESSIBLE OPERON because transcription is
INHIBITED when tryptophan binds to the regulatory protein.
INDUCIBLE OPERONs are STIMULATED when a INDUCIBLE OPERONs are STIMULATED when a specific small molecule interacts with a
regulatory protein.Examples of Inducible Operons:
the lac operon
the ara operon
INDUCIBLE OPERONS: The lac Operon The lac OPERON is also positively regulated by cyclic AMP (cAMP) and the regulatory protein, cAMP receptor protein (CRP).
Activated CRP stimulates transcription.
Without cAMP, transcription levels are low, even in the presence of Lactose! You Try!
1.With your group, represent how the araoperon we will use in lab might workoperon we will use in lab might work.
2. Fill-in the table provided to generate your hypothesis and predictions for your lab work this week! (Each group should turn in one sheet with their pre-lab!)
What is a Virus? Obligate Intracellular Parasites!
Viruses are classified according to several characteristics:
Whether the genome is DNA or RNA g Whether the nucleic acid is single-stranded
or double-stranded Whether the shape of the virion is simple or
complex Whether the virion is surrounded by a
Viral Life Cycles
Lets Watch: http://www.hhmi.org/biointeractive/media/viral_lifecycle-lg.mov
The Lytic Cycle
Switching Between Lysogenic and Lytic Cycles Requires Regulation!
Virus(a ss RNA Virus)
An Aside: Viral Recombination
Sample Lifecycle: the HIV
Virus(another ss RNA
Viruses Also Infect Plant CellsPlant viruses do not use membrane receptors but rather take advantage of mechanicalmethods to enter the cell.