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
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
The 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.
