To understand how enzymes can be specific, we should consider enzyme structure and the Lock and Key Model of enzyme function. Recall that a protein is composed of one or several long chains of amino acids attached together, and that each amino acid chain folds into a specific 3-dimensional shape based on the amino acid sequence and how the individual amino acids in the chain interact with each other and with the surrounding solution. Enzymes are folded up in such a way so that they have an indentation, or a pocket on their surface. This pocket is called the active site . So the lactose molecule fits perfectly into the active site of the lactase enzyme, meaning that the lactase enzyme can only catalyze the breakdown of lactose.
Enzymes carry out hundreds of chemical reactions that are essential for our survival.
They carry out the reactions necessary for our digestion of foods, for the build-up and break down of DNA and RNA, as well as many other vital processes. Lactose intolerance can be overcome by swallowing tablets containing lactase enzymes before eating dairy products.