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Biotechnology Unit: Increasing
Variation through DNA Transfer
How does a bacterium fight off antibiotics?
The three main ways are:
1. Membrane proteins called efflux pumps literally
pump the antibiotics out of the cell.
2. The prokaryote can produce an enzyme that will
degrade the antibiotic.
3. The prokaryote can produce an enzyme that will
change the structure of the antibiotic.
• Change in STRUCTURE = Change in FUNCTION
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How do these organisms become so resistant?
1.
Natural, or inherited, resistance
– The prokaryote might have been born without the proper cellular
structures (transport system, membrane receptors, etc.) needed for
the antibiotic to be effective.
2. Acquired Resistance
– The organism obtains the needed resistance gene from another
source, which it incorporates into its genome.
3. Random mutations
– It has been estimated that one in every 108 – 109 bacteria will
develop resistance when exposed to an antibiotic. This might seem
like a rare event but please remember that bacterial growth is VERY
rapid.
– This new gene is then given to all the new progeny. This process is
known as vertical gene transfer.
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Horizontal Gene Transfer
There are ways, other than mutations, in which prokaryotes
obtain antibiotic resistance through horizontal gene transfer.
• Transformation
– the update of naked DNA (usually a plasmid) by a
prokaryote
• Transduction
– viral transmission of genetic information
• Conjugation
– One bacterium gives resistance to another bacterium.
• Transposition
– Movement of DNA segments within and between DNA
molecules
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Transformation
Transformation causes a
change in the genotype, and
even possibly the phenotype,
and occurs when a cell takes
in foreign genetic material
and incorporates it into its
own.
• This causes the cell to
become a recombinant
cell, i.e. one that contains
genetic material from
more than one source.
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Transduction
Transduction is the
process of viruses
carrying prokaryotic
genes from one
bacterium to another.
Do you remember how Hershey
and Chase demonstrated that it
was DNA, and not protein, that
was the genetic material?
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Transduction
• The bacteriophage
injects its genetic
material into the cell.
• The bacterial DNA
breaks apart.
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Transduction
• The viral DNA uses the
cell’s machinery to
make more viruses.
• Some of the viruses end
up with the host cell’s
genetic material.
8
Transduction
• The virus particles with
the host cell’s genetic
material inject it into
another cell.
• The new cell
incorporates this new
DNA into its own.
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Transduction
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Conjugation
Conjugation
Some Prokaryotes can use a “sex pilus” and a
“mating bridge” to transfer genetic information from
one cell to another. Only one cell needs to have a
pilus to perform conjugation.
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Conjugation
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Horizontal Gene Transfer
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Transposition
Transposons have been
characterized as “jumping
genes.”
• Small DNA segments can be
transferred from one place
on a chromosome to another
in the cell by:
– “Cut and Paste”
– “Copy and Paste”
– Retrotransposon movement
• An RNA intermediate is made
and is used to make a new DNA
segment using reverse
transcriptase. That DNA is then
inserted elsewhere in the
genome.
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Transposons
In 1983, at the age of 81,
Barbara McClintock won
the Nobel Prize for her
discovery of “jumping
genes” in corn.
• You can see how
transposons have varied
not only the genotype, but
also the phenotype (kernel
color) of this corn cob.
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Coming up!
The next presentation will be on
Genetic Engineering!
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Created by:
Jason Walker
Science Coordinator
National Math + Science Initiative
Dallas, TX