Question

Explain the mechanism of anaerobic respiration.

Answer 1

Hint: It is a multistep process that occurs in the absence of oxygen and involves several enzymes for the production of energy. Less amount of energy is produced by this process due to the partial oxidation of the sugar molecule.

Complete answer:Anaerobic respiration is the process of energy production in the absence of oxygen. This process commonly occurs in the cytoplasm of the cell. It is found in some bacteria and fungi. Two ATP molecules are produced.
It involves three steps- glycolysis, decarboxylation, and reduction. which has been explained as follows.
Glycolysis or EMP pathway is a ten-step enzyme-catalyzed partial oxidation of glucose that results in the formation of two molecules of pyruvate $(C{H}_{3}COCOOH)$, $$2NAD{H}_2$$ and 2 ATP molecules.
$C_6{H}_{1}2O_6+2ADP+2P_{(i)}\to 2C{H}_3-CO-CO{O}^{-}+2ATP+2NAD{H}_2$
Decarboxylation leads to the removal of carbon dioxide from the pyruvate to form acetaldehyde$$(C{H}_{3}CHO)$$. This reaction takes place in the presence of pyruvate decarboxylase and TPP.
$$2C{H}_{3}COCOOH\to 2C{H}_{3}CHO+2C{O}_2$$
Reduction occurs by two different mechanisms which depend upon the type of organism involved.
Alcohol fermentation- Dehydrogenase enzyme catalyzes the reduction of acetaldehyde to ethanol.
$$2C{H}_{3}CHO+2NAD{H}_2\to 2C_2{H}_{5}OH$$
Lactic acid fermentation- In some bacteria, the decarboxylation step does not take place and pyruvate undergoes reduction to form lactic acid.
$2C{H}_{3}COCOOH+2NAD{H}_2\to 2C{H}_{3}CH(OH)COOH+2NA{D}^{+}$

Note: The mechanism of anaerobic respiration is similar to that of aerobic respiration up to glycolysis. Glycolysis breaks down glucose to form pyruvate. Pyruvate is anaerobically broken down into various products depending upon the organism or tissue. The two most common products are ethanol and lactic acid.