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Biology 110 - Basic Concepts and Biodiversity

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Prokaryotes II - Structure and Function

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Bacteria containing a lot of peptidoglycan in their cell walls also tend to have less complex cell walls, and are called gram-positive bacteria. Conversely, gram-negative bacteria have less peptidoglycan, but have more complex cell walls overall. In particular, the gram-negative bacteria have an additional outer membrane with attached lipopolysaccharides. Most Gram-negative bacteria also have fimbriae; hair-like projections, external to the cell wall, that allow the bacteria to stick to the cells they infect.

Some of these lipopolysaccharides are toxic, serving to counteract the natural defenses of the host organism. Also, the additional membrane of gram-negative bacteria can make them more resistant to antibacterial medications (antibiotics). For these two reasons, a gram-negative bacterial infection can be far more severe than a gram-positive infection.

Many pathogenic diseases are caused by gram-negative bacteria. Do a Web search on Yersinia pestis.  What disease does this bacterium cause in humans?

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Prokaryotes can use carbon in a variety of forms, both as an energy source and as a precursor for anabolic reactions. As you've learned, carbon dioxide is the simplest form of carbon used. Organisms that use this simple form of carbon are often called "carbon fixers." (You will learn more about this process in the photosynthesis tutorials 26 and 27)

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Figure 5. The Exxon Valdez oil tanker. (Click to enlarge).  The Exxon Valdez ran aground in Alaska's Prince William Sound in the spring of 1989, dumping approximately 11-million gallons of oil.  Photo source: Office of Response and Restoration, National Ocean Service, National Oceanic and Atmospheric Administration

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Most prokaryotes use sugars (monosaccharides and disaccharides) and complex carbohydrates (e.g., starch) as a carbon source. However, very unusual forms of carbon can also be used by some prokaryotes. For example, some prokaryotes can feed on oil. Although a bane to the oil fields, these oil-eating bacteria have been used to help clean oil spills (Figure 5).

Some bacteria are capable of using synthetically produced carbon compounds such as TNT (used as an industrial and military explosive) and PCBs (banned substances which are persistent organic pollutants in the environment) as a carbon source. These bacteria metabolize these compounds and produce nontoxic by-products. Humans have exploited this ability by using various species of bacteria for the removal of toxins from the environment; a process known as bioremediation. There is an emerging field of civil engineering that utilizes bacteria (along with other eukaryotic microorganisms) for the purpose of cleaning contaminated soils, wells, and river sediments.

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  • bioremediation
  • capsule
  • cell wall
  • chemoautotroph
  • chemoheterotroph
  • endospore
  • endotoxin
  • exotoxin
  • flagellin
  • flagellum (pl. flagella)
  • fimbriae
  • gram-positive
  • gram-negative
  • Gram's stain
  • lipopolysaccharide
  • peptidoglycan
  • photoautotroph
  • photoheterotroph
  • plasma membrane
  • sporulation
  • taxis
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Questions?  Send your instructor a message through ANGELCanvas!

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