Microbial metabolism
- Rock
- NealC
- zxwang
- NealC
- Carl_Ross
- Carl_Ross
- NealC
- corrol
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» Rock - Pasteur and Metabolism
In 1861, Louis Pasteur observed that when yeast grow in a sugar and protein medium completely free of air, they ferment vigorously, and for every gram of yeast that forms, 60-80 grams of sugar disappear. If the experiment is carried out in the presence of air, for one gram of yeast that forms, only 4-10 grams of sugar are removed. The yeast again ferment if transferred to a sugar-containing medium absent of air. When the experiment is repeated with a protein medium, the yeast grow only in the presence of oxygen. Pasteur concluded that the yeast can take oxygen from air, and in the absence of air, the yeast take oxygen from the sugar.Pasteur applied quantitative methods to his studies of fermentation and was the first to report on organisms that could live and reproduce in the absence of oxygen. His conclusion was, however, incorrect. These different behaviors of yeast are known today as the Pasteur effect.
Please explain the three yeast behaviors based on modern conepts of microbial metabolism.
What was incorrect about Pasteur's conclusion?
Thanks,
Rocco Pizza
-- posted by Rock
» NealC - Please explain the three yeast behaviors based on modern conepts
Please explain the three yeast behaviors based on modern conepts of microbial metabolism.Less suger was used per gram of organism when the organisms grew in oxygen because more ATP could be generated. Anaerobically grown organisms only breakdown the sugar via glycolysis and can not use the TCA cycle and the electron transport chain to generate more ATP. Aerobically grown organisms can utilize the TCA and ETC portions of their degradation pathways and generate much more ATP. ATP is the energy the cells use to produce protein, DNA, etc. in order to grow and multiply. More ATP=more yeast cells.
Aerobically grown yeasts given only protein for a carbon source can breakdown the protein to amino acids but require a functioning TCA cycle and an ETC to generate ATP. When the yeast cells are grown anaerobically the TCA cycle and ETC do not work and as a result no energy and no growth of anaerobically grown yeast with protein as a carbon source.
What was incorrect about Pasteur's conclusion?
It wasn't how the oxygen was obtained that allowed the growth of the organisms. It was the ability of aerobically grown organisms to further reduce the sugars to carbon dioxide and water that results in more ATP generation. More ATP more cell mass.
-- posted by NealC
» Carl_Ross - Pasteur
To be picky with your response:The stated conclusion was that necessary oxygen was obtained from the sugar. This is incorrect, because no oxygen is required for the fermentation. Chemoheterotrophs using anaerobic metabolism transfer electrons to organic compounds rather than inorganic compounds such as oxygen. For example, pyruvate becomes lactic acid.
-- posted by Carl_Ross
» Carl_Ross - Artificial evolution
The term refers to a technique which artificially generates a large number of mutations in a cDNA (cloned DNA for one gene) or the protein it encodes. The gene products are then subjected to a screening process which allows identification of improved versions. You could visit the web sites of Maxygen, Inc. or Diversa Corporation, or contact someone there for more information.-- posted by Carl_Ross
-- posted by corrol
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