The substrate is like a key. Yes, for a given enzyme the substrate fits into the active site of an enzyme. But if you want this analogy to better describe the physical changes to the substrate, you have to visualize the key being cut in half by the lock. This is the affect that hydrolitic enzymes have on their specific substrate.
METAMIA is a free database of analogy and metaphor. Anyone can contribute or search. The subject matter can be anything. Science is popular, but poetry is encouraged. The goal is to integrate our fluid muses with the stark literalism of a relational database. Metamia is like a girdle for your muses, a cognitive girdle.