Enzymes are biological catalysts that speed up chemical reactions in living systems without being used up. They make reactions fast enough for cells to grow, repair, move materials, and release energy. Most enzymes are proteins with a specific three-dimensional shape that helps them recognize the molecules they act on.
Understanding enzyme catalysis connects chemistry, biology, medicine, and biotechnology.
Key Facts
- Enzymes lower activation energy, so reactions occur faster at the same temperature.
- E + S ⇌ ES ⇌ E + P represents enzyme, substrate, enzyme-substrate complex, and product.
- Reaction rate usually increases with substrate concentration until the enzyme becomes saturated.
- Lock-and-key model: the substrate fits into a pre-shaped active site.
- Induced-fit model: the active site changes shape slightly when the substrate binds.
- Temperature, pH, substrate concentration, enzyme concentration, and inhibitors all affect enzyme activity.
Vocabulary
- Enzyme
- An enzyme is a biological catalyst that speeds up a chemical reaction without being permanently changed.
- Substrate
- A substrate is the reactant molecule that binds to an enzyme and is converted into product.
- Active site
- The active site is the specific pocket or groove on an enzyme where the substrate binds and the reaction occurs.
- Activation energy
- Activation energy is the minimum energy needed for reactant molecules to reach the transition state and react.
- Inhibitor
- An inhibitor is a molecule that decreases enzyme activity by blocking binding or changing the enzyme's shape.
Common Mistakes to Avoid
- Saying enzymes add energy to a reaction is wrong because enzymes lower the activation energy barrier rather than supplying the reaction energy.
- Assuming enzymes are consumed during reactions is wrong because enzymes are regenerated after product release and can catalyze many cycles.
- Thinking every substrate fits every enzyme is wrong because active site shape, charge, and chemical groups make enzyme binding highly specific.
- Ignoring pH and temperature is wrong because changes in these conditions can alter enzyme shape and reduce or destroy catalytic activity.
Practice Questions
- 1 An uncatalyzed reaction has an activation energy of 80 kJ/mol. With an enzyme, the activation energy is 35 kJ/mol. By how many kJ/mol did the enzyme lower the activation energy?
- 2 An enzyme converts 240 substrate molecules into product in 30 seconds. What is the average reaction rate in molecules per second?
- 3 A student says the lock-and-key model and induced-fit model mean the same thing. Explain the difference between the two models and why induced fit often gives a more realistic description of enzyme action.