Respiratory pathway is believed to be a catabolic pathway. However, nature of TCA cycle is amphibolic. Explain.
Living cells obtain energy through respiration, It is the process of generating energy in the form of ATP molecule by breaking down food molecules like glucose, fats, etc.
The process starts with glycolysis which occurs in cytoplasm producing pyruvic acid. It is then converted to acetyl Co-A, which enters mitochondria! matrix. This initiates the tricarboxylic acid cycle.
This cycle is said to be arnphibolic because many intermediate compounds formed in this cycle act as precursors for biosynthesis of many important biological molecules, i.e., co-enzymes, vitamins, hormones. Besides this, many molecules, i.e., fatty acids, aminoacids, co-enzymes etc, can enter this cyclo directly.
Acetyl Co-A is related to the synthesis and breakdown of fatty acids, steroids, carotenoids terpenes and aromatic compounds. α- ketoglutarate and oxaloacetate are raw materials for the synthesis of amino acids like glutamate and aspartate and also pyrimidines and alkaloids. Succinyl forms pyrrole compounds like cytochrome and chlorophyll.
So, it is the cycle Mere both breakdown and synthesis reactions keep on going simultaneously. the following figure shows interrelationship among metabolic pathway showing respiration mediated break down of the different organic molecule.