6a.+Bacterial+Transformation

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Introduction
Bacteria have evolved a way to exchange small pieces of genetic material amongst themselves without the need for sexual reproduction. It is this natural technique that we are going to hijack and use for our own purposes.

Bacterial Transformation
In Bacterial Transformation, we are going to give a bacterial strain a new trait. This trait is carried on a small circular piece of DNA called a plasmid. Bacteria exchange these plasmids regularly, as they commonly provide a beneficial adaptation. We are going to take advantage of all these characteristics, and let the machinery of //E coli// do the hard work of replicating a piece of DNA along the way.


 * Transformation is the alteration of a bacterial cell’s genotype by the uptake of naked, foreign DNA from the surrounding environment.
 * For example, harmless //Streptococcus pneumoniae// bacteria can be transformed to pneumonia-causing cells.
 * This occurs when a live nonpathogenic cell takes up a piece of DNA that happens to include the allele for pathogenicity from dead, broken-open pathogenic cells.
 * The foreign allele replaces the native allele in the bacterial chromosome by genetic recombination.
 * The resulting cell is now recombinant, with DNA derived from two different cells.
 * Years after transformation was discovered in laboratory cultures, most biologists believed that the process was too rare and haphazard to play an important role in natural bacterial populations.
 * Researchers have since learned that many bacterial species have surface proteins that are specialized for the uptake of naked DNA.
 * These proteins recognize and transport DNA from closely related bacterial species into the cell, which can then incorporate the foreign DNA into the genome.
 * While //E. coli// lacks this specialized mechanism, it can be induced to take up small pieces of DNA if cultured in a medium with a relatively high concentration of calcium ions.
 * In biotechnology, this technique has been used to introduce foreign DNA into //E. coli//.

View the powerpoint presentation below to learn the steps of bacterial transformation.
 * [[file:Bacterial Transformation PowerPoint.ppt]]

Multimedia
Watch below as a plasmid is exchanged between two bacterial cells.

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Practice Quiz
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Practice Free Response Questions
//Answer the following question on a loose sheet of paper (or word process it). When completed, compare it to the rubric below, and determine your score.//

1. Describe how a plasmid can be genetically modified to include a piece of foreign DNA that alters the phenotype of bacterial cells transformed with the modified plasmid. Describe a procedure to determine which bacterial cells have been successfully transformed.