Abstract
Systems biology, metabolomics, metabolic engineering, and other recent developments in biochemistry suggest that future biochemists will require a detailed familiarity with the compounds and pathways of intermediary metabolism and their biochemical control. The challenge to the biochemistry instructor is the presentation of metabolic pathways in a manner that allows student creativity in learning the pathways and their components. One approach that does permit the use of problem solving for the study of metabolic pathways involves following the fate of ^13^C, ^14^C, or ^15^N labels, presented originally in the structure of an important metabolic starting compound, through relevant metabolic pathways. This method allows the presentation and study of problems in which such an isotopic label can be traced through two or more metabolic pathways, thus illustrating how these pathways are interconnected. The understanding that all the pathways of intermediary metabolism are interconnected provides opportunities to discuss their metabolic control by such mechanisms as signaling, feedback inhibition, location in organelles, coenzyme levels, and coenzyme recycling rates. The method is illustrated by following the fate of ^14^C labels through anaerobic glycolysis, gluconeogenesis, and fatty acid transport, Ξ²βoxidation, and ketone body formation. Cholesterol biosynthesis and heme formation are used to show that presentations of long and complex pathways can demonstrate important biochemical concepts by following the fate of an isotopic label using only the most important intermediates. Problems based on tracing radioactive labels through one or more metabolic pathways allow the use of cooperative learning techniques.