Metabolic pathways are controlled by the presence or absence of particular enzymes in the metabolic pathway, as well as through the regulation of rate of reaction of key enzymes within the pathway
Genes for some enzymes are continually expressed and therefore these enzymes are always present in the cell. They are controlled by the regulation of their rate of reaction
The active site of an enzyme changes shape to better fit the substrate after the substrate binds
The substrate molecules have a high affinity for the active site, but the subsequent products have a low affinity, allowing them to leave the active site
The final product in the metabolic pathway reaches a critical concentration and inhibits an earlier enzyme, blocking the pathway and preventing further synthesis of the end-product