Enzymes are proteins that act as biological catalysts - this means they speed up reactions without being used up.
An enzymeProteins that act as biological catalysts, meaning they speed up reactions without being used up themselves. works on the substrateA substance on which enzymes act., forming products.
An enzyme’s active siteRegion of an enzyme where the substrate attaches. and its substrate are complementaryShapes that fit together like jigsaw pieces. in shape.
An enzyme will only work on one substrate - it is substrate specific.
Enzymes and substrates collide to form enzyme-substrate complexes.
The substrates are broken down (or in some cases built up).
The products are released.
The enzyme is free to act again.
This theory is known as the ‘lock and key model’.
It explains why each enzyme will only work on one substrate.
For example, the active site of amylaseAn enzyme that can break down starch into simple sugars. is only complementary to starch and will therefore only break down starch, not protein or fat.
Enzyme
Substrate
Product
Carbohydrase
Carbohydrate
Simple sugar, glucose
Amylase
Starch
Simple sugar, glucose
Protease
Protein
Amino acid
Lipase
Fat (lipid)
Glycerol and fatty acids
Enzyme
Carbohydrase
Substrate
Carbohydrate
Product
Simple sugar, glucose
Enzyme
Amylase
Substrate
Starch
Product
Simple sugar, glucose
Enzyme
Protease
Substrate
Protein
Product
Amino acid
Enzyme
Lipase
Substrate
Fat (lipid)
Product
Glycerol and fatty acids
Inhibitors
Inhibitors are molecules that partially fit into an enzyme’s active site but are not broken down.
They inhibit the reaction.
As long as they are in the active site the substrate cannot enter to be broken down, thus reducing the rate of reaction.
