Forming an Enzyme-Substrate Complex
- Enzymes are globular proteins required in metabolic pathways
- Virtually every metabolic reaction within living organisms is catalyzed by an enzyme – enzymes are therefore essential for life
- Enzymes have an active site where specific substrates bind forming an enzyme/substrate complex
- The active site of an enzyme has a specific shape to fit a specific substrate
- Extremes of heat or pH can change the shape of the active site, preventing the substrate binding – this is called denaturation
- Substrates collide with the enzyme's active site and this must happen at the correct orientation and speed in order for a successful reaction to occur
- An enzyme-substrate complex forms when an enzyme and its substrate join together
- The enzyme-substrate complex is only formed temporarily (a few nanoseconds) before the enzyme catalyzes the reaction and the product(s) are released
Formation of an Enzyme / Substrate Complex Diagram
The active site of an enzyme has a specific shape to fit a specific substrate (when the substrate binds an enzyme-substrate complex is formed)
- The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate(s)
- The lock and key hypothesis likens this relationship to the fitting of a key into a specific lock
- The shape of the active site is determined by the complex tertiary structure of the protein that makes up the enzyme:
- Proteins are formed from chains of amino acids held together by peptide bonds
- The order of amino acids determines the shape of an enzyme molecule
- If the order is altered, the resulting 3D shape changes
Enzyme Specificity Diagram
An example of enzyme specificity – the enzyme catalase can bind to its substrate hydrogen peroxide as they are complementary in shape, whereas DNA polymerase is not
Exam Tip
Don't forget that both enzymes and their substrates are highly specific to each other – this is known as enzyme / substrate specificity.