<P> The term amphibolic is used to describe a biochemical pathway that involves both catabolism and anabolism . </P> <P> This term was proposed by B. Davis in 1961 to emphasise the dual metabolic role of such pathway . The citric acid cycle (The Krebs Cycle) is a good example of amphibolic pathway . The first reaction of the cycle, in which oxaloacetate (a four carbon compound) condenses with acetate (a two carbon compound) to form citrate (a six carbon compound) is typically anabolic . The next few reactions, which are intramolecular rearrangements, produce isocitrate . The following two reactions are typically catabolic . COO is lost in each step and succinate (a four carbon compound) is produced . </P> <P> There is an interesting and critical difference in the coenzymes used in catabolic and anabolic pathways; in catabolism NAD+ serves as an oxidizing agent when it is reduced to NADH . Whereas in anabolism the coenzyme NADPH serves as the reducing agent and is converted to its oxidized form NADP+ . </P>

Explain giving examples what is meant by the statement that the citric acid cycle is amphibolic