![]() ![]() Monod’s microbiology mentor André Lwoff suggested to Monod that such lags might be caused by the requirement to induce the synthesis of enzymes that had not been needed while glucose was present. During this diauxic shift, the population of cells experiences a “lag” (delay) in growth. coli cells presented with a mix of glucose and lactose will induce the lac operon after glucose has been depleted. Thus, the operon is transcribed at a high level only when glucose, the preferred sugar, is absent. When the catabolite activator protein is bound to cAMP, it binds to DNA and stimulates transcription of the lac operon. ![]() Catabolism of glucose leads to a low concentration of cyclic adenosine monophosphate (cAMP). The lac operon, which encodes proteins necessary to metabolize lactose, is a prime example of catabolite repression, which underlies the diauxic shift. Recent advances in probing metabolic and regulatory mechanisms inside cells, and in surveying natural variation of many species, make the time ripe to revisit the connections between gene regulation, physiology, and ecology. Fewer biologists read Monod’s principles of microbial growth under nutrient limitation or stop to reflect on the ecological implications of how microbes regulate their metabolisms. Indeed, the form in which most students of biology now encounter the diauxic shift is in the canonical example of gene regulation: the lac operon of the gut bacterium Escherichia coli. Although Monod had a deep appreciation of evolution, his standing as one of the great biologists of the modern era stems from his pursuit of the molecular mechanisms underlying the diauxic shift. The diauxic shift links physiology and ecology and therefore must be understood in terms of the evolutionary fit of an organism to its environment. ![]() In his doctoral thesis, Jacques Monod described the diauxic shift, whereby a microbial population consumes all of a preferred sugar before metabolizing a less-preferred sugar. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |