Enzymes

• Enzymes

  Biological catalysts
• Enzymes

  • They are large biological molecules found in living organisms
  • They can speed up chemical reactions without themselves being chemically changed at the end of the reaction
• Catalyst

  A substance that can speed up a chemical reaction, without itself being chemically changed at the end of the reaction
• Enzymes in living things are biological catalysts which speed up chemical reactions without themselves being changed at the end of the reaction
• Enzymes

  • They are proteins in nature that are folded into specific three-dimensional shapes to allow them to interact with specific molecules, known as substrates, in a precise way
  • Enzyme names end with the -ase suffix after the adoption of the -ase naming system
• Enzyme-catalysed reactions

  • They catalyse many of the chemical reactions that occur in living organisms
  • They are produced only when they are needed
• Enzyme-catalysed reactions

  1. Break down complex substances into simpler ones

  2. Build up complex substances from simpler ones
• Enzyme-catalysed reactions that break down complex substances

  • Catalase breaks down hydrogen peroxide into water and oxygen
  • Enzymes in cellular respiration break down glucose to release energy
  • Digestive enzymes break down large food molecules into small, soluble substances
• Enzyme-catalysed reactions that build up complex substances

  • Enzymes in cytoplasm link amino acids to form polypeptides/proteins
  • Enzymes in plants synthesise glucose from carbon dioxide and water during photosynthesis
• Digestive enzymes

  Enzymes involved in digestion
• Digestive enzymes

  • Amylase (digests starch to maltose)
  • Maltase (digests maltose to glucose)
  • Protease (digests proteins to polypeptides, then to amino acids)
  • Lipase (digests fats to fatty acids and glycerol)
• Enzyme specificity

  • A chemical reaction inside a cell is catalysed by a unique enzyme
  • Enzyme specificity is determined by the folding of a protein into a unique three-dimensional (3-D) structure that contains a specific region called the active site
  • Only substrates with a complementary shape can bind to the active site and undergo a chemical reaction (lock-and-key hypothesis)
• Enzyme-catalysed reaction

  E + S ⇌ ES ⇌ E + P
• Characteristics of enzymes

  • Sensitivity to temperature
  • Sensitivity to pH
  • Remain unchanged at the end of reaction and required in minute amounts
  • Speed up chemical reactions
  • Specific in action
• Effect of temperature on enzyme activity

  1. At low temperature, the enzyme is less active

  2. As the temperature increases, the rate of enzyme reaction increases

  3. The enzyme is most active at the optimum temperature

  4. As the temperature increases beyond the optimal temperature, the enzyme activity reduces quickly

  5. All the enzyme molecules have been denatured
• Denaturation

  The change in the three dimensional structure of an enzyme or any other soluble protein, caused by heat or chemicals such acids or alkalis
• Sensitivity to pH

  • Enzymes work optimally at specific pH values, which vary between different types of enzymes
  • Changes in pH can alter the shape of the active site of the enzyme, affecting its ability to bind with the substrate and perform its function
  • Extreme pH changes may denature enzymes, as they are protein in nature