Final answer:
The lock-and-key hypothesis was outdated by the induced fit model, which more accurately represents the dynamic nature of enzyme-substrate interactions.
Step-by-step explanation:
The lock-and-key hypothesis suggested an enzyme's active site was a fixed structure that only allowed a matching substrate to bind, much like a lock would only accept a specific key. However, this model did not adequately capture the dynamic nature of enzyme-substrate interactions. The more refined induced fit model describes how enzymes can undergo a conformational change to accommodate the binding of a substrate, adjusting their shape for an optimal fit, akin to a handshake or a hug. This latter model is supported by evidence that, for instance, hexokinase changes conformation upon binding with glucose, rather than binding without change or requiring an effector molecule at an allosteric site.