AQA A Level Biology复习笔记1.4.13 Models & Functions of Enzyme Action

Students should be able to: Appreciate the Models & Functions of Enzyme Action


Models of enzyme action

  • Scientists often use models to explain their observations from experiments
  • As technology and research advances within a field new models can be developed and old ones disproven
  • The lock and key model covered at GCSE was originally thought to be an accurate model of enzyme action
    • It suggested that the rigid shape of the active site of the enzyme was a precise fit for the specific shape of the substrate


  • New techniques have allowed scientists to discover that proteins are not rigid structures
    • Experiments showed that multiple regions of an enzyme molecule moved in response to the environment
    • Many of these movements were minimal but some of them were more significant
    • The larger movements occurred when the substrate bound to the enzyme


  • These findings led to the now widely accepted induced fit model
    • Prior to binding, the substrate and active site and not completely complementary in shape
    • When the substrate binds the active site alters shape and moulds around the substrate


  • There is evidence to support the induced fit model:
    • X-ray diffraction techniques allow for 3D pictures of molecules to be formed
    • This technique was used to produce pictures of the enzyme hexokinase before and after it bound to its substrate glucose
    • The images confirmed that the active site of the enzyme changed shape after the substrate bound



The lock-and-key hypothesis




The induced-fit hypothesis