CHAP 4

• Biological catalysts


  Large biological molecules called enzymes
• Enzyme


  A substance that can speed up a chemical reaction without being chemically changed itself
• Enzymes are proteins that function as biological catalysts
• Enzymes catalyse the rate of chemical reactions but remain chemically unchanged
• Enzymes


  • They catalyse the rate of chemical reactions
  • They remain chemically unchanged
• Substrate


  Large/insoluble food molecules that cannot diffuse through the cell membrane
• Role of enzymes


  1. Break down large molecules into simpler substances

  2. Allow soluble/diffusible substances to pass through cell membrane
• Enzymes


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


  Each chemical reaction is catalysed by a unique enzyme
• Lock and key hypothesis


  The 3D shape of an enzyme affects the way it functions
• Active site


  Grooves on the surface of an enzyme molecule where substrates can fit
• Enzyme catalysis


  1. Substrate binds to active site

  2. Enzyme-substrate complex forms

  3. Reactions at active site convert substrate to product

  4. Enzyme is released unchanged
• Enzymes


  • They speed up chemical reactions by lowering activation energy
  • They have specific action
  • They bind to substrates with complementary shape
  • They remain unchanged and can be reused
• Temperature increases


  Rate of enzyme reaction increases
• Temperature increases further


  Rate of enzyme reaction decreases due to denaturation
• Denaturation


  Change in 3D structure of enzyme caused by heat, chemicals or pH
• Denatured enzymes no longer act as catalysts
• Optimum pH


  pH at which enzymes work best
• Enzymes


  • Protease in stomach works best at pH 4
  • Protease in small intestine works best at pH 7