A Level Biology Revision "The Induced Fit Model of Enzyme Action"

Enzymes and Active Sites00:00:06

Enzymes are globular proteins with a specific 3D active site where substrate molecules attach to form an enzyme-substrate complex. The active site's tertiary structure is specific to the substrate, explaining enzyme specificity. Temporary bonds formed between the substrate and active site amino acids lower the activation energy, increasing the reaction rate.

The Lock and Key Model00:00:58

Initially, scientists believed the active site's tertiary structure was fixed, meaning the substrate fit perfectly like a key in a lock. This model is known as the lock and key hypothesis.

The Induced Fit Model00:01:19

Later, it was discovered that the lock and key model was incorrect. The induced fit model states that the active site's tertiary structure changes as the substrate approaches. As the substrate forms bonds with amino acids, the enzyme adjusts, molding tightly around the substrate to ensure a perfect fit and catalyze the reaction.

Explaining Enzyme Specificity with Induced Fit00:01:57

Molecules that are not substrates cannot form the correct bonds with the active site's amino acids. Consequently, the enzyme's tertiary structure doesn't change, and the active site doesn't adjust, which explains why enzymes are specific to their substrates. Experiments have confirmed that the induced fit model is correct.