Enzymes catalyze the many reactions in a cell. there are hundreds of different enzymes in a cell-each with a unique three-dimensional shape. why do cells have so many different enzymes?

To ensure that they can only catalyse specific reactions. The unique 3D shape of each enzyme means that only a specific substrate that is complementary (fits into the active site of the enzyme) will bind to the enzyme to be hydrolysed. In this way, the metabolic reactions of the body can be controlled.