Fermentation

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dan167
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Fermentation

Post by dan167 » Mon Aug 14, 2006 2:05 am

Hey im currently doing As biology and have some questions about fermentation.

if the equation for fermentation using a yeast catalyst is:

C6H12O6 ----------> 2C2H5OH + 2CO2 + 2ATP

How come none of the oxygen was used by the yeast?

Also how does the yeast increase the rate of reaction? Do they lower the energy requirement for glycolysis? or do they play a role with the NADH ect.

Thankyou

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mith
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Post by mith » Mon Aug 14, 2006 5:51 am

Umm, 1st law of thermodynamics....did you expect to see lesser oxygen atoms?
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dan167
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Post by dan167 » Mon Aug 14, 2006 12:08 pm

No :oops: im just confused...I basically want to know what yeast does to the reaction and how it survives.

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MrMistery
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Post by MrMistery » Mon Aug 14, 2006 6:30 pm

Yeast undergoes glycolysis just like every other organism on the planet. As you might now, glycolysis produces 2 molecules of ATP, 2 molecules of pyruvate and 2 molecules of NADH. Ok, if oxygen is present, then cellular respiration can go on with the Krebs cycle and oxidative phosphorilation. But the problem is when there is no oxygen present in the medium. the yeast can survive with only 2 molecules of ATP/glucose. But in order for glucose to keep running, there must be free NAD+ atoms to keep accepting electrons in phase 6 of glycolysis. This means that the NADH atoms somehow need to be recycled. The cell does this by the process of fermentation. How? Well, firstly the molecules of pyruvate glycolysis produces are turned into CH3-CH=O(acetaldehyde) and CO2. Then the acetaldehyde molecules accept electrons from NADH and turn to ethanol. This process keeps glycolysis running by producing more NAD+ molecules, but unlike oxidative phosphorilation, produces no ATP during this recycling.
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