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Natural intolerance of species

  1. Sep 3, 2014 #1
    Except E.Coli that are lactose intolerant, are there any other species that are xxx intolerant in nature you have experimented with ?
  2. jcsd
  3. Sep 3, 2014 #2


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    E. coli are not lactose intolerant. They contain a set of genes (the lac operon) to allow for the metabolism of lactose. While lactose is not the preferred carbon source for E. coli (glucose is), in the absence of glucose, E. coli will transcribe the lac operon and begin producing the enzymes necessary to metabolize lactose. The molecular events that regulate how the bacteria turn the lac operon on and off is one of the best studied systems in molecular biology, and the study of this system formed the foundation for the 1965 Nobel Prize in medicine.

    However, back to the original question, there are a great deal of examples of substances that one organism can metabolize, but other organisms cannot. For example, most species cannot digest cellulose except for certain bacteria and organisms that harbor those bacteria in their gut.
  4. Sep 3, 2014 #3
    Thanks for correction,
    The lac operon link you provide talks about E.coli and its lactose metabolism as the studied model, but I wonder whether or not such an enzyme synthesis process at the genetic level occurs the same in all other species that are xxx-tolerant as well (e.g a patient suffering from sucrose intolerance).
  5. Sep 3, 2014 #4


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    Yes, in some cases, xxx-intolerance can be caused not by faults in the enzyme themselves but in the DNA sequence responsible for turning expression of those enzymes on or off. A good example here is lactose intolerance in humans. Most mammals have a perfectly functioning copy of the gene for lactase, the enzyme that digests lactose. However, because mammals consume their mother's milk only during childhood, expression of that enzyme gets turned off into adulthood, resulting in lactose intolerance. Sometime during human evolutions, certain populations of humans acquired a mutation that prevented the lactase gene from being turned off. This results in lactase expression persisting into adulthood, allowing adult humans harboring that mutation to digest lactose into adulthood.
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