Answer:
each substrate has a unique 3-dimensional shape.
Step-by-step explanation:
Enzymes are large and complex globular proteins that have one or more polypeptide chains. The part of the enzyme responsible for its action is the active center (site). The shape of the active center is very precisely adjusted to the substrate, similar to the key to the lock.
Due to the presence of the active site, the enzymes show a specificity property, which means that each enzyme acts on only one compound or group of similar compounds.