Introduction to Metabolism

Metabolism consists of all the biochemical reactions in an organism and is divided into the catabolic and anabolic pathways.

Catabolic pathways break down complex molecules like carbohydrates, lipids, and proteins into smaller units. These pathways are typically exergonic, that is, they release energy.

Anabolic pathways use this energy to combine simpler substances to form complex macromolecules such as proteins, nucleic acids, and polysaccharides.

Amphibolic pathways, such as the reactions of the Krebs cycle, participate in both catabolism and anabolism, breaking down molecules for energy while also supplying intermediates for biosynthesis.

This coupling of catabolic and anabolic reactions improves energy efficiency, allowing a balanced flow of energy for cellular activities.

Metabolic pathways are highly regulated to maintain homeostasis.

Feedback inhibition primarily regulates enzyme activity in metabolic pathways. The final product of a pathway inhibits an enzyme early in the same pathway.

For example, in isoleucine synthesis, high levels of isoleucine block the enzyme threonine deaminase, preventing the overaccumulation of the product.