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

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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.

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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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ConjugationSome 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

Conjugation

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Horizontal Gene Transfer

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TranspositionTransposons 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 WalkerScience CoordinatorNational Math + Science InitiativeDallas, TX