Pharma gyan Pandit

 Fermentation

 Not all organisms are able to use oxygen in metabolism.  Even organisms such as ourselves that are highly evolved still have some means to extract energy, even if oxygen is in short supply.  These processes which derive energy in the absence of oxygen are known as fermentation.  We will look at two major pathways for fermentation

           

   a.  Alcohol fermentation in microorganisms-->  produces ethanol

   b.  Lactic acid fermentation in muscle -->  produces lactate

 Fermentation is essentially a modification of glycolysis that enables the reduced NADH to be reoxidized to NAD⁺, so it can be used again.  Figure 9.17a summarizes the process of alcohol fermentation. 

Glucose is broken down in glycolysis producing pyruvate and a net yield of 2 ATP.  In two additional steps, pyruvate is converted to acetaldehyde and then to ethanol while the NADH formed during glycolysis is reoxidized to regenerate more NAD⁺, so fermentation can continue. 

  glucose ---->  2 pyruvate ----> 2 acetaldehyde + 2CO₂ --> 2 ethanol

Fermentation is essential for the brewing industry in the production of beer, wine, and other alcoholic beverages.  Yeast, which are simple eukaryotic cells can carry out the fermentation of sugars such as glucose to yield alcohol.  Other microbes such as some bacteria are also able to carry out fermentation.

We are also able to regenerate more NAD⁺ from NADH in the absence of oxygen during oxygen deprivation of muscle cells.  This process is called lactic acid fermentation and is shown in Fig. 9.17b.  In this pathways the products of glycolysis (2 pyruvate) are reduced to give 2 lactate with regeneration of NAD+ from NADH.

            glucose --> 2 pyruvate --> 2 lactate

 During the early stages of strenuous exercise when sugar breakdown to produce ATP is occuring at a faster rate than oxygen can arrive in the blood, much of the pyruvate is converted to lactate in muscle.