What does enzymes work in one direction or the other but not both mean?

The phrase "enzymes work in one direction or the other but not both" means that enzymes catalyze specific reactions in a particular direction, either facilitating the conversion of substrates into products or the reverse, but not simultaneously. This directional specificity is due to the enzyme's active site, which is designed to bind only certain substrates and promote a specific reaction pathway. As a result, an enzyme can either help build molecules (anabolic reaction) or break them down (catabolic reaction) but not do both at the same time. This characteristic ensures metabolic efficiency and regulation within biological systems.