Increasing Variation through DNA Transfer - PowerPoint Presentation

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Increasing Variation through DNA Transfer

Biotechnology Unit

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How does a bacterium fight off antibiotics?The three main ways are:Membrane proteins called efflux pumps literally pump the antibiotics out of the cell.

The prokaryote can produce an enzyme that will degrade the antibiotic.The prokaryote can produce an enzyme that will change the structure of the antibiotic. Change in STRUCTURE = Change in FUNCTION

How do these organisms become so resistant?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.Acquired Resistance The organism obtains the needed resistance gene from another source, which it incorporates into its genome.

Random mutationsIt 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.

Horizontal Gene TransferThere are ways, other than mutations, in which prokaryotes obtain antibiotic resistance through

horizontal gene transfer. Transformationthe update of naked DNA (usually a plasmid) by a prokaryote

Transduction viral transmission of genetic informationConjugationOne bacterium gives resistance to another bacterium.

TranspositionMovement of DNA segments within and between DNA molecules

TransformationTransformation 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.

TransductionTransduction 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?

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.

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.

Transduction

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.

Conjugation

Conjugation

Horizontal Gene Transfer

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.

TransposonsIn 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.