Enzymes (Cambridge International AS Biology)

Enzymes as Proteins

Spec point — 3.1.1 · state that enzymes are globular proteins that catalyse reactions inside cells (intracellular enzymes) or are secreted to catalyse reactions outside cells (extracellular enzymes)

• Enzymes are biological catalysts

  • ‘Biological’ because they function in living systems
  • ‘Catalysts’ because they speed up the rate of chemical reactions without being used up or changed

• Enzymes are also globular proteins

• Critical to the enzyme's function is the active site where the substrate binds

• Metabolic pathways are controlled by enzymes in a biochemical cascade of reactions

  • Virtually every metabolic reaction within living organisms is catalysed by an enzyme – enzymes are therefore essential for life to exist

• Enzymes can be intracellular or extracellular referring to whether they are active inside or outside the cell respectively

  • Intracellular enzymes are produced and function inside the cell
  • Extracellular enzymes are secreted by cells and catalyse reactions outside cells (e.g. digestive enzymes in the gut)

Exam Hint Don't forget that enzymes are proteins and so anything that could denature a protein, rendering it non-operational (extremes of heat, temperature, pH etc.) would also denature an enzyme.