Enzyme-controlled Reactions (WJEC GCSE Biology)

Revision Note

Cara Head

Author

Cara Head

Last updated

Enzyme Specificity

  • Enzymes control chemical reactions, meaning that they convert substrate molecules into products
  • The conversion of a substrate into a product occurs when the substrate attaches to a region of the enzyme known as the active site
  • Enzymes are specific to one particular substrate; this is because the shape of the active site is complementary to the substrate

Enzyme specificity diagram

enzyme-substrate-specificity-igcse-and-gcse-biology-revision-notes

Enzymes are specific to one particular substrate as the active site is complementary in shape to the substrate

The 'lock and key' model

  • This model of enzyme action states that the substrate fits into the active site of an enzyme very precisely, like a key going into a lock

Lock and key model diagram

 lock and key model of enzyme actionThe active site and the substrate are complementary to each other, meaning that the substrate fits into the active site like a key into a lock

Molecular collisions

  • During an enzyme-catalysed reaction the following sequence of events occurs:
    • Enzymes and substrates randomly move about in solution
    • Enzymes collide with their complementary substrate molecules and the reaction occurs
    • The product forms and is then released from the active site
    • The enzyme is unchanged and will go on to catalyse further reactions
  • Enzyme activity will increase or decrease depending on the number of molecular collisions
    • When more collisions occur between enzyme and substrate molecules the rate of reaction will increase and more product will be produced
    • Fewer enzyme and substrate collisions will slow the rate of reaction and result in less product

Examiner Tip

You should NEVER say that enzymes and substrates have a matching structure, or that their structures are the same. Enzymes and substrates have a complementary structure to each other, meaning that they fit together like pieces of a jigsaw puzzle. 

Enzyme-substrate Complexes

Higher Tier Only

  • When an enzyme and complementary substrate collide the substrate binds to the active site of the enzyme; this forms an enzyme-substrate complex
  • The enzyme-substrate complex is a temporary structure; after the enzyme catalyses the reaction then the products are released and the active site is free to form another enzyme-substrate complex

Enzyme-substrate complex diagram

formation-of-an-enzyme-substrate-complex

A substrate binds to the active site of an enzyme, forming an enzyme-substrate complex

You've read 0 of your 10 free revision notes

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

Did this page help you?

Cara Head

Author: Cara Head

Expertise: Biology

Cara graduated from the University of Exeter in 2005 with a degree in Biological Sciences. She has fifteen years of experience teaching the Sciences at KS3 to KS5, and Psychology at A-Level. Cara has taught in a range of secondary schools across the South West of England before joining the team at SME. Cara is passionate about Biology and creating resources that bring the subject alive and deepen students' understanding