Q.Explain the lock-and-key model and the induced-fit model of enzyme action, and state one respect in which the induced-fit model better explains observed enzyme behaviour.

[!TLDR]

Lock-and-key: rigid active site exactly matches substrate (Fischer, 1894). Induced-fit: flexible active site reshapes around substrate (Koshland, 1958) -- better explains the small conformational changes actually observed on binding. …

The lock-and-key model, proposed by Emil Fischer in 1894, treats the enzyme's active site as a rigid structure whose shape is already precisely complementary to its substrate, in the way that only one key fits a given lock -- this explains why enzymes are so specific for their substrates. The induced-fit model, proposed by Daniel Koshland in 1958, instead treats the active site as flexible, changing shape slightly as the substrate binds and moulding around it for a closer fit, much as a glove adjusts as a hand is inserted. The induced-fit model is generally considered the more accurate of the two, because it better accounts for the small but real conformational changes that are actuall …

Contrast the two models on the single axis of active-site flexibility (rigid vs reshaping), then state the specific observation (co …

Presenting the two models as though only one can ever be correct for any enzyme, rather than as historically successive refinements add …