What is a metabolic pathway?

Learning objectives

To illustrate a metabolic pathway as a sequence of biochemical reactions.
To explain how a genetic defect can cause the absence of a downstream enzyme / protein and the accumulation of upstream metabolites.

A metabolic pathway is a sequence of biochemical reactions in a specific order. Each reaction is catalyzed by a specific enzyme. The substrate of a reaction is transformed into a product. The latter becomes the substrate for the next biochemical reaction and so on. Glycolysis is an example of a metabolic pathway.