Anaerobic Respiration

Anaerobic respiration

Anaerobic respiration first studied by Kostychev (1902), Anaerobic respiration is an enzyme-controlled, partial break down of organic compounds (food) without using oxygen and releasing only a fraction of the energy. It is also called intra-molecular respiration (Pfluger, 1875). Anaerobic respiration occurs in the roots of some water-logged plants, certain parasitic worms (Ascaris and Taenia), animal muscle and some microorganisms (bacteria, moulds). In microorganisms anaerobic respiration is often called fermentation.

Higher organism like plants can not perform anaerobic respiration for long. It is toxic because accumulation of end products, insufficient amount of available energy and causes stoppage of many active process.

Process of anaerobic respiration : In this process pyruvate which is formed by glycolysis is metabolised into ethyl alcohol or lactic acid and CO₂ in the absence of oxygen. Glycolysis is occurs in cytoplasm so the site of anaerobic respiration is cytoplasm.

C₆H₁₂O₆ $\to$ 2C₂H₅OH + 2CO₂ + 52 Kcal/218.4 kJ

(1) Formation of ethyl alcohol : When oxygen is not available, yeast and some other microbes convert pyruvic acid into ethyl alcohol.

(2) Production of lactic acid : In this process hydrogen atoms removed from the glucose molecule during glycolysis are added to pyruvic acid molecule and thus lactic acid is formed.

Lactic acid is produced in the muscle cells of human beings and other animals.

Pasteur effect : The process may be defined as “the inhibition of sugar breakdown due to the presence of oxygen under aerobic condition” and the reaction is called Pasteur reaction. Dixon (1937) stated that the Pasteur effect is the action of oxygen is checking the high rate of loss of carbohydrate and in suppressing or diminishing the accumulation of products of fermentation.”

Fermentation : Fermentation is a kind of anaerobic respiration carried out by microorganisms fungi and bacteria. In microorganism the term anaerobic respiration is replaced by fermentation (Cruickshank, 1897) which is known after the name of its major product, e.g., alcohol fermentation, lactic acid fermentation.

(1) Butyric acid fermentation : It occurs in bacteria Clostridium butyricum.

\mathop {{C_6}{H_{12}}{O_6}}\limits_{{\text{(hexose)}}}#xA0\to \mathop {{C_4}{H_8}{O_2}}\limits_{{\text{(butyric}}\,{\text{acid)}}}#xA0+ 2{H_2} + 2C{O_2}

 \mathop {2{C_3}{H_6}{O_3}}\limits_{{\text{(lactic}}\,{\text{acid)}}}#xA0\to \mathop {{C_4}{H_8}{O_2}}\limits_{{\text{(butyric}}\,{\text{acid)}}}#xA0+ 2{H_2} + 2C{O_2}

(2) Lactic acid fermentation : It occurs in lactic acid bacteria and muscles.

\mathop {{C_{12}}{H_{22}}{O_{11}}}\limits_{{\text{(lactose)}}}#xA0+ {H_2}O \to \mathop {{C_6}{H_{12}}{O_6}}\limits_{{\text{(glucose)}}}#xA0+ \mathop {{C_6}{H_{12}}{O_6}}\limits_{{\text{(galactose)}}}

\mathop {\mathop {{C_6}{H_{12}}{O_6}}\limits_{(hexose)}#xA0\to \mathop {2{C_3}{H_6}{O_3}}\limits_{(lactic\,acid)} }\limits_{}

(3) Acetic acid fermentation : It occurs in acetic acid bacteria.

\mathop {{C_2}{H_5}OH}\limits_{({\text{ethyl}}\,{\text{alcohol}})}#xA0+ {O_2} \to \mathop {C{H_3}COOH}\limits_{({\text{acetic}}\,{\text{acid}})}#xA0+ {H_2}O + {\text{energy}}.