In 1961, B. Davis was credited with coining the word amphibolic pathway. Any biochemical pathway which involves both metabolic processes i.e. catabolism and anabolism are known as an amphibolic pathway. The amphibolic pathway can be best explained by Krebs’ cycle.
Generally, cellular respiration is the biochemical process of breaking down of glucose to release energy. Among the carbohydrates, glucose is the common substrate for energy production. Other compounds used for energy production include fats and proteins. But energy cannot be produced directly from these substrates hence they are formerly converted into simpler forms. For example, fats on lysis give glycerol and fatty acids. Fatty acids are converted to acetyl CoA whereas glycerol is transformed into 3-phosphoglyceraldehyde (PGAL) which then enter the respiratory pathway. While proteins break down into amino acids by the enzyme called proteases. Based on the type of amino acid they will either form pyruvate or acetyl-CoA or follow the Krebs’ cycle and complete the process of respiration.
Respiration is the breakdown of the complex compounds into simple ones to produce energy molecule, ATP. Hence the process is called catabolic process and the pathway is termed as a catabolic pathway. Actually, respiration is the result of both making and breaking. When energy is required, proteins or fatty acids are broken down to form acetyl-CoA and further processes of respiration occur. This is catabolism. When the body requires fatty acids or proteins, respiratory pathway stops and the same acetyl-CoA is utilized and fatty acids are manufactured via respiration. This process of synthesis is termed as anabolism. Thus we can say respiration is the sum process of catabolism and anabolism. Hence, the respiratory pathway is known as an amphibolic pathway.
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