Enzymes – Biological Catalysts

Definition of Catalysts & Enzymes

• Catalyst: substance that speeds up a reaction but is unchanged afterward.
• Enzymes = biological catalysts produced by cells (intracellular or secreted).
• Example reaction: $2H<em>2O</em>2 \rightarrow 2H<em>2O + O</em>2$ (catalysed by catalase, foaming from released $O_2$).

Structure of Enzymes

• All enzymes are proteins: long amino-acid chains folded into a precise 3-D shape.
• Common examples: catalase, amylase, pepsin, trypsin, pectinase, lactase, proteases.

Enzyme Action

• Active site: region where reaction occurs.
• Substrate: molecule that binds to active site.
• Product: molecule(s) released after reaction.
• Enzyme is unchanged and reusable after product release.

Specificity (Lock-and-Key)

• Active-site shape complements only one substrate (or substrate type).
• Precise fit → enzyme specificity.

Factors Affecting Activity

Temperature

• Low $T$: slow rate (low kinetic energy).
• Rate rises with $T$ until optimum (≈ $40^{\circ}\text{C}$).
• Above optimum: enzyme denatures → active site shape lost → rapid rate decline.

pH

• Each enzyme has an optimum pH; outside this range it denatures.
• Examples: pepsin optimum ≈ acidic; amylase optimum ≈ neutral.

Applications / Examples

• Detergent proteases: hydrolyse coloured protein stains → cleaner clothes at lower $T$.
• Pectinase: degrades apple cell-wall pectins → higher juice yield.
• Lactase: splits lactose → glucose + galactose, allowing lactose-free milk.
• Seed germination: amylase converts starch → maltose for embryo nutrition.

Key Terms

• enzyme, catalyst, catalyse
• substrate, active site, product
• temperature, optimum, denature
• pH, catalase, amylase, pectinase, trypsin, pepsin, lactase, protease