Final answer:
An enzyme is like a lock and key because its active site has a specific shape that only fits certain substrates, allowing for specific chemical reactions to occur. It's referred to as the lock-and-key model. However, the induced fit model further refines this concept by showing that enzymes can slightly adjust their shape to better accommodate the substrate.
Step-by-step explanation:
The analogy of an enzyme being like a lock and key in a chemical reaction comes from the lock-and-key model which suggests that the active site of an enzyme has a specific shape into which only a complementary substrate (or substrates) can fit. Like a key fits into a lock, the substrate enters the enzyme's active site and forms an enzyme-substrate complex that facilitates the chemical reaction without undergoing any permanent change itself. This is because the active site and the substrate have complementary structures and bonding groups, as depicted in the lock-and-key model.
While this model has been a fundamental concept in biochemistry, scientists have developed a more refined understanding known as the induced fit model. This model suggests that while the enzyme's active site may have an initial shape that is complementary to the substrate, it can undergo a slight conformational change to securely bind the substrate, much like a glove that molds to the shape of a hand. This ensures the substrate is correctly positioned to facilitate the chemical transformation into the product(s) of the reaction.