Week 6.docx - Week 6 Chapter 9 Gene Transfer and Genetic...

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Week 6: Chapter 9 Gene Transfer and Genetic Engineering Bacterial cells can have their genetic information altered by DNA polymerase that makes a mistake during DNA replication Chemicals and radiation can damage DNA in bacterial cells and alter their genetic information in that damaged cell Once a microorganism gains a resistance gene, it is more than willing to share it with other microorganisms Organisms in our bodies could potentially pick up an antibiotic resistance o Problems come when bacteria in our normal flora pass that antimicrobial resistance gene to a pathogen Types and Significance of Gene Transfer Gene Transfer – refers to the movement of genetic information between organisms Recombination – the combining of genes (DNA) from two different cells Vertical gene transfer – when genes pass from parents to offspring Horizontal (lateral) gene transfer – pass genes to other microbes of their same generation Bacterial DNA Transfer Transformation (think of naked DNA) o A change in an organism’s characteristics because of transfer of genetic information o Naked DNA – DNA that has been released from an organism after the cell is lysed and DNA is no longer incorporated into chromosomes o Competence factor is released into the medium and apparently facilitates the entry of DNA into cell Competence factor – a surface protein that binds extracellular (“naked”) DNA and enables the cell to be transformed Competence – ability of a cell to alter its genetics by taking up extracellular (“naked”) DNA from its environment in the process called transformation o DNA transport proteins and DNA exonuclease (an enzyme that cuts up DNA) are also needed o Griffith’s experiment: Pneumococci with capsules produce smooth (S-type), glistening colonies.
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Those lacking capsules produce rough (R-type) colonies with a coarse, nonglistening appearance. Only the capsule producing (encapsulated) pneumococci inoculated into mice were pathogens—that is, they had the power to cause disease (pneumonia). One such organism can multiply rapidly and kill a mouse! Mice are said to be “exquisitely” sensitive to pneumococci; therefore, they make excellent test animals. Capsules help prevent molecules produced by the mouse’s immune system from reaching the surface of the bacterium. They also make it difficult for white blood cells to engulf the invading bacteria. In other words, the capsule protects the bacteria from the mouse’s immune system. Process: Griffith injected one group of mice with heat-killed smooth pneumococci, a second group with live smooth pneumococci, a third group with live rough pneumococci, and a fourth group with a mixture of live rough and heat-killed smooth pneumococci.
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