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Questions about fermantation and respiration concepts

  1. Feb 14, 2005 #1
    if you increase the # of yeast cells, then how will it affect the ATP production of cells if the sugar concentratin is held constant?

    If u substitute galactose for glucose, then how will the rate of atp production byh the cells be affected if the amt of yeast in the experimenent is held cosntant?
     
  2. jcsd
  3. Feb 14, 2005 #2

    iansmith

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    This relates to biochem. In a close system, what happen when you add more enzyme but keep the substrate constant. This should give you the answere you are looking for.

    This is tricking. Is it under anaerobic (fermentation) or aerobic (respiration) conditions? Unlike glucose, yeast process galactose differently under anaerobic condition compare to aerobic condition.
     
  4. Feb 14, 2005 #3
    if substrate is held constant, then adding more enzymes will have no affect on the rate of reaction right?

    so for #1, the rate of ATP production of cells if the sugar concentratin is held constant wont be affected at all?

    for #2, i believe that this is a anaerobic process since we are dealing with yeast cells here
     
  5. Feb 14, 2005 #4

    Moonbear

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    Remember, reaction rate depends on both the amount of substrate and the amount of enzyme. Remind yourself of enzyme-substrate reactions. Your text should have graphs illustrating the reaction rates plotted for varying enzyme or substrate amounts. This is one of those places in biology where you need to connect the concepts presented in one chapter (enzyme-substrate reactions) with those in another chapter (cellular respiration).

    Yeast can survive under aerobic conditions as well as anaerobic. Have you covered both aerobic and anaerobic respiration already?
     
  6. Feb 14, 2005 #5
    ok i am still confused about #1

    Well for enzymes and substrate, if the enzymes are held constant and substrate are increased, then it will increase the rate of reaction until the enzymes get saturated with substrate, where only increasing the amt of enzymes will increase the rate of reation

    But if the substrate is held at a constant lvl, then wouldnt the enzymatic rate of reaction be the exact same, since if u increase the # of enzymes, it wont make a difference, since there is only a constant supply of substrate, and none is being added to the closed system?

    and for #2, i reread the question and it says in fermentation, which is anaerobic
     
  7. Feb 14, 2005 #6

    Moonbear

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    Okay, going back through the thread, I've confused myself (and probably you too) by misreading.

    I think for the first part, you need to assume the cells don't have any constraints on enzyme availability. I think you need a two-part answer here. Think about substrate availability. As you increase the number of yeast cells, initially the rate will change (you tell me what direction), but when you add a lot more cells, what happens to the sugar available, and what does that do to the rate of reaction?

    Okay, now compare the net ATP production for the reactions starting with glucose vs galactose. That's all it's asking you to do.

    I think we misled you suggesting you look at enzyme-substrate reactions to answer the question...however, there is a problem here with your understanding of those, so maybe it was fortuitous so you can make sure you've got that right too. What is the role of an enzyme in a reaction? If you have no enzyme, does the reaction occur spontaneously? When you add enzyme, assuming you have no limit to your substrate, what happens? If you add more enzyme, again, with no limit to the amount of substrate, what happens? Now, turn the question around. If you have only a limited amount of substrate, and add just a little enzyme to it, do you have a changing rate of reaction, or is it constant? What about when you run out of substrate? Now, if you add back substrate, but keep the same amount of enzyme as you had before, is the reaction rate different from the first time you added substrate?

    Remember, rate of reaction is not synonymous with amount of product. It refers to how quickly you get that product.
     
  8. Feb 15, 2005 #7
    If you increase the number of yeast cells, then the rate of atp production will increase

    If you add a lot more yeast cells, then the sugars will all be used up (saturated) faster and eventually the rate of atp production will level out

    Is my thinking correct?

    If you add enzyme, the rate of reaction will increase
    If you add more enzyme, the rate of reaction will increase faster and eventually level out as all the products get saturated and level out.

    If you have limited amount of substrate, and add a little enzyme to it, the rate of reaction will increase, but when u run out of substrate, then wouldnt there be no rate of reaction, since all the substrate is used up?

    If you add back substrate, but keep the amt of enzyme you had before, then the rate of reaction will again increase until its all used up...

    man this part of bio is really confusing me....

    anyways, were my conceptual thinking right or am i missing some key point or overlooking something?

    thanks

    and for question #2

    For glucose, when it undergoes glycolysis in fermantation, 2 ATP is produced.

    But for galactose, i have no idea what the ATP output is, I cant seem to find it anywhere in my book

    Thanks
     
    Last edited: Feb 15, 2005
  9. Feb 15, 2005 #8

    Moonbear

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    Yep, you got it.


    Correct. Now I think you've got it.

    I had to go look this up myself (it's been a while since I've had to think about yeast respiration, so I was hoping iansmith might return before then; he's the microbiologist here). I think it may be a trick question :rolleyes:
    According to this site http://www.accessexcellence.org/AE/AEC/AEF/1995/goodman_respiration.html your average grocery store variety of yeast doesn't use galactose, so I'm guessing that's what you're supposed to assume here.

    Under aerobic conditions, some yeast can use galactose as a substrate, but that's probably not the answer your teacher expects you to know.
     
  10. Feb 15, 2005 #9

    iansmith

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    That correct and that was the tricky part of the question, because most people would assume that yeast would utilize galactose in the same manner as glucose. Galactose is not a fermentable sugar but it can be used, in some case, for aerobic resperiration.
     
  11. Feb 15, 2005 #10

    DocToxyn

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    What about maltose? I read in a baking book from which I am building a sourdough starter that wild yeast strains, such as those found on organic rye flour do not use maltose. However, commercial strains of yeast, such as those found in little packets in the store will use maltose as well as other sugars. The whole point is to leave enough maltose for lactobacilli to "team up" with the wild yeast in the culture so one can develop a sour-tasting bread.
     
  12. Feb 15, 2005 #11

    iansmith

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    Wild yeast and commercial yeast are often different species. Also, commercial yeast have been selected for their ability to ferment maltose to alcohol.

    When brewing beer, wild yeast contamination often results in undersireable products because it will fermented sugars that are not fermented by the brewer yeast.

    Also sugar utilization between species of yeast varies greatly from one to another.
     
  13. Feb 15, 2005 #12
    why is that in respiration but not fermentation galactose can be used as a sugar for a source for ATP?

    Well im assuming it has something to do with glucose undergoing glycolysis...

    Does galactose undergo glycolysis?

    or are there other factors contributing to the fact that galactose cant be fermantized
     
    Last edited: Feb 15, 2005
  14. Feb 15, 2005 #13

    iansmith

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