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Why Do We Study Bacteria?

  • Bacteria have a major impact on human life; some are harmful pathogens, while others have positive effects on health.

  • Bacteria play an essential role in nature's chemical recycling, and biotechnologists have utilized bacteria to produce useful products.

  • The abundance of bacteria on earth reflects a rapid reproductive rate and ability to survive harsh conditions.

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How Does Bacterial Genetics Differ From That of Eukaryotes?

  • Bacteria have a simpler chromosome structure than eukaryotes that allows rapid replication.

  • Many bacteria have additional genes in the form of plasmids.

  • Bacteria do not engage in sexual reproduction, but they can transfer DNA to increase genetic diversity.

    • Conjugation involves the direct transfer of a DNA strand from one bacterium to another.

    • In a process called transformation, one bacterium takes up DNA expelled from a dead bacterium.

    • In transduction, a virus transfers bacterial genes from one bacterium to another.

    • If DNA is transferred between bacteria of two different species, it is called horizontal transfer.

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What Are Viruses?

  • Viruses are familar to us as a source of disease, but are they cells?

    • Viruses have a very simple structure, consisting of nucleic acid and a few enzymes surrounded by a protein coat.

    • Viruses invade a cell and use the cell's machinery to replicate themselves.

  • There are many different viruses that infect plants, animals and even bacteria.

  • Many human diseases are caused by viruses.

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How Do Viruses Infect Cells and Are There Other Kinds of Infectious Agents?

  • Viruses replicate within cells in two major ways depending on their type of genetic material.

    • If viruses have DNA as the genetic material, the host cell replicates the viral DNA, transcribes it, then translates the viral RNA.

    • If viruses have RNA as the genetic material, the first step is synthesis of viral DNA through use of a
      viral enzyme called reverse transcriptase.

  • The immune system can kill cells infected with a virus; HIV, the AIDS virus, is especially deadly because it infects the helper T cells of the immune system.
  • Viroids are pieces of "naked" RNA that infect plant cells.

  • Unusual proteins called prions cause neurodegenerative diseases in mammals.

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