Anaerobic Respiration : Fermentation

The respiration which takes place in absence of oxygen is called anaerobic respiration. There are two views about the origin of fermentation:

(a)    It is an evolutionary bypass. Some organisms use to keep glycolysis functioning under anaerobic conditions.

(b)    It is a biochemical remnant. It has evolved very early in the history

of life. At that time the earth’s atmosphere contained no oxygen.       •
Strong evidences are present. These evidence shows that the common descent of organisms from primitive cells. In these cells glycolysis and fermentation first appeared. It still persists.

  • The glycolysis generates the hydrogen atoms. ‘Nese atoms are donated to organic molecules in fermentation. Following reactions occur:
  1. Lactic acid fermentation

The NADH reduces the Pyruvate to form lactic acid. This reaction occurs in the mammalian muscles and certain fungi. The animal used NADH, to reduce the pyruvate. This reaction is controlled by an enzyme lactate dehydrogenase.

  1. Alcoholic fermentation

The NADH, reduces the pyruvate into alcohol. It takes place in some fungi (yeast) and bacteria. The glucose is not completely degraded during fermentation. Therefore, a large amount of unusable energy still remains in the products. Only two molecules of ATP are formed during glycolysis and no more ATp is produced. Fermentation is used only to regenerate NM). It produces ethanol as by product. This reaction is .controlled by enzyme pyruvate decarboxylase and alcohol dehydrogenase.

Two types of organisms can carry out fermentation:


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  • Obligative anaerobic: Obligative anaerobic organisms include certain types of bacteria. These organisms survive only in the complete absence of molecular oxygen. Its example is clostridium sp.
  • Facultative anaerobic: Facultative anaerobic organisms and tissues include certain bacteria, yeasts, and cells. These organisms can ferment nutrients in absence of oxygen. It also generates sonic ATP. It also provides NAD for glycolysis. Facultative anaerobic organisms and tissues carry our more efficient energy harvesting in the presence of oxygen.

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