alcoholic fermentation vs. lactic acid fermentation

[kb09026]

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Why do some organisms undergo alcoholic fermentation while others undergo lactic acid fermentation? I understand the difference between the two (at least when it comes to products) and that yeast generally goes alcoholic while certain bacteria and animals undergo lactic acid fermentation, but why does it happen this way?

 

[eDITN]

Biochemically, there is no difference between the rationale behind these two reactions. In both cases, the goal is to regenerate NAD+ in order to drive glycolysis (and produce ATP) in the absence of oxygen.

Yeast (and some bacteria) simply have the enzymes necessary to ferment via the alcohol mechanism whereas most organisms undergo fermentation by producing lactic acid.

 

[Hexon]

does this mean fish get drunk on the alcohol?😛

 

[gmcguitar4]

Yeast produce ethanol because it is toxic to other competitor bacteria and relatively harmless to themselves. Multicellular organisms have no need for this.

Interesting fact: Cancer cells use anaerobic metabolism for energy and actually despise oxygen. But they do this at a rate about 8 times higher than normal cells. Google the Lindau Lecture of 1966.

 

[Morsetlis]

Why do some organisms undergo alcoholic fermentation while others undergo lactic acid fermentation? I understand the difference between the two (at least when it comes to products) and that yeast generally goes alcoholic while certain bacteria and animals undergo lactic acid fermentation, but why does it happen this way?

I know nothing about yeasts and I don't want to know anything about yeasts until next year. On the other hand...

Alcohol fermentation produces alcohol from sugars, or specifically, oxidizes ethanol from pyruvate. Lactic acid fermentation (in animals) produces lactic acid from the reduction of pyruvate which is the product of glycolysis. Lactic acid fermentation regenerates NAD+.

If the animal were to produce alcohol instead, they'd turn around and oxidize the alcohol to generate more NADH, increasing the NADH/NAD+ ratio and make the alcohol fermentation moot (the whole point was to regenerate NAD+). If the animal had lactic acid, that could get converted back into pyruvate in the liver for gluconeogenesis (which incidentally completes the Cori cycle that uses up ATP from fatty acid beta oxidation for NAD+ regeneration and gluconeogenesis).

On the other hand, in animals, alcohol just get oxidized to acetaldehyde, then acetic acid, and then CO2 and water. This process generates NADH (reducing equivalent, which will convert into energy in the mitochondria / electron transport chain).

 

[tamakisuououran]

Yeast produce ethanol because it is toxic to other competitor bacteria and relatively harmless to themselves. Multicellular organisms have no need for this.

Interesting fact: Cancer cells use anaerobic metabolism for energy and actually despise oxygen. But they do this at a rate about 8 times higher than normal cells. Google the Lindau Lecture of 1966.

Hey you say the byproducts of alcohol fermentation are harmeless to yeast. I was wondering if thats true (and im not saying it is or its not) then why woudl the yeast die after going through the process. I remember reading somewhere that they die after the lactic acid fermentation?
Am I mistaken over here?
thanks