Can you please explain the lock and key model of enzyme action to me?

Okay, so let's get back to basics. What is an enzyme? An enzyme is a biological catalyst that speeds up chemical reactions. How does it do this? All enzymes have active sites, which is where certain molecules bind. These have a specific shape that are only complementary to specific molecules, called enzyme substrates. This means that only the substrates that can fit into the enzyme's active site are going to bind to it. Once they bind, they form enzyme-substrate complexes, and the enzymes can then take them through a different reaction pathway that requires less energy for the reaction to take place, and so the activation energy, which is the energy required to initiate a reaction, becomes lower. So overall, the reaction happens faster. Once the reaction is complete, the enzyme lets go and releases the substrate, meaning the enzyme's active site is now free once again, and another substrate can come along and the reaction can take place again.