AQA A Level Biology

Revision Notes

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

_Lock and key hypothesis, downloadable AS & A Level Biology revision notes

The lock-and-key hypothesis

Induced fit hypothesis, downloadable AS & A Level Biology revision notes

The induced-fit hypothesis

Exam Tip

Enzymes have a wide variety of functions within organisms. They catalyse both intracellular and extracellular reactions which determine the structures and functions of not only cells but the whole organism!

Author: Amelia

While studying Biochemistry at Oxford University, Amelia started her own tutoring service, helping to connect Science tutors with students in her local area. Amelia has experience teaching the sciences and Maths at all levels to UK and international students and, as well as being our Biology Lead, designs revision resources for Chemistry.

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