Metabolism encompasses all the chemical reactions occurring within an organism, playing a crucial role in maintaining life. These reactions are organized into metabolic pathways, which are sequences of chemical transformations that modify a substrate multiple times before yielding a final product. For instance, consider a metabolic pathway where substrate A is converted into product B by enzyme 1. However, product B is not the end result; it is further transformed into C by enzyme 2, then into D by enzyme 3, and finally into the ultimate product E by enzyme 4. In this context, E represents the final product of the pathway, while A, B, C, and D serve as intermediates or substrates for the enzymes involved.
Enzymes are essential in facilitating these reactions, working collaboratively in a series of steps to ensure the efficient conversion of substrates into products. This organized approach to chemical reactions is what defines a metabolic pathway. Understanding these pathways is fundamental to grasping how organisms process energy and materials, and it sets the stage for exploring the two primary types of metabolic pathways, which will be discussed further in subsequent lessons.