Amphibolic pathway can be described as a kind of biochemical pathway which involves both Anabolism and catabolism pathways.
The term amphibolic pathway is coined by B. Davis in the year 1961.
Catabolism : A biochemical pathway where large molecules are broken down into smaller molecules. It can be by means of Hydrolysis and Oxidation.
Hydrolysis : Bigger molecules into smaller molecules to release energy. eg: Breaking down a protein into amino acids, or a triglyceride into fatty acids, or a disaccharide into monosaccharides.
Oxidation: It involves removal of hydrogens and electrons (redox reactions) from an organic molecule and use the free energy released to synthesize ATP. eg : Cellular respiration.
Anabolism: A biochemical pathway which involves merging of smaller simple precursors into large and complex molecules. eg: Photosynthesis
Respiration as an example of amphibolic pathway:
In cellular respiration all the complex compounds like glucose, protein and fat break down into simpler forms and produce ATP.
Glucose enters respiration by Glycolysis, Krebs cycle and oxidative phosphorylation to produce ATP.
The proteins will be first degraded by proteases into amino acids and depending on the structure of amino acids, they will enter cellular respiration either as pyruvic acid or acetyl co A.
Fats will be first broken into glycerol and fatty acids. Later fatty acids find their way into cellular respiration by getting converted into acetyl Co A, whereas glycerol needs to to PGAL to enter respiration.
This part of the respiration is termed as catabolism, as large molecules are broken down into smaller molecules.
When organisms needs to synthesize fatty acids , acetyl Co A will be withdrawn from respiratory process and used for producing fatty acids.
Similarly, for synthesis of anabolic precursors for amino-acid synthesis- intermediates of Krebs cycle such as α-ketogluturate and oxaloacetate are used for biosynthesis of amino acids.
The above reactions are best examples of respiration working as an anabolic process.
As the respiratory pathway is involved in bot catabolism and anabolism process, it is better to consider respiratory pathway as amphibolic pathway rather than only catabolic process.
