enzymes

• Enzymes


  Large proteins that catalyse (speed up) reactions
• Enzymes are not changed in the reactions they catalyse
• Lock and key theory

  1. The enzyme's active site (where the reaction occurs) is a specific shape

  2. The enzyme (the lock) will only catalyse a specific reaction because the substrate (the key) fits into its active site

  3. At the active site, enzymes can break molecules down into smaller ones or bind small molecules together to form larger ones

  4. When the products have been released, the enzyme's active site can accept another substrate molecule
• Digestive enzymes


  Convert food into small, soluble molecules that can then be absorbed into the bloodstream
• Digestive enzymes


  • amylase
  • proteases
  • lipases
• As the temperature increases

  The rate of reaction increases
• Optimum temperature


  • This is when the reaction works as fast as possible
• Denaturation


  The shape of the enzyme's active site is changed by heat or extreme pH, so the substrate no longer fits into the active site and the enzyme cannot catalyse the reaction
• At extremes of pH or at very high temperatures


  The shape of an enzyme's active site can change
• Different enzymes have different optimum pH values, which allows them to be adapted to work well in a range of environments with different pH values
• When the active site breaks down, an enzyme becomes denatured - it is incorrect to say the enzyme has died or been killed
• Enzymes


  Protein molecules that catalyse specific reactions in organisms
• Enzymes


  • Each enzyme only catalyses a specific reaction, because the active site only fits together with certain substrates (like a lock and key)
• Amylase


  Breaks down starch into glucose
• Where amylase is produced


  Salivary glands, pancreas, and small intestine
• Proteases


  Break down proteins into amino acids
• Where proteases are produced

  Stomach, pancreas, and small intestine
• Lipases


  Break down lipids into fatty acids and glycerol
• Where lipases are produced

  Pancreas and small intestine
• Factors that affect the rate of enzyme activity

  • Temperature
  • pH
• Denatured


  The shape of an enzyme's active site is changed by high temperatures or an extreme pH, so it can no longer bind with the substrate
• As temperature increases

  Rate of reaction increases until it reaches the optimum for enzyme activity - above this temperature enzyme activity decreases and eventually stops
• pH


  Different enzymes have a different optimum pH at which their activity is greatest - a pH much lower or higher than this enzyme activity decreases and stops
• Different parts of the digestive system have very different pHs - the stomach is strongly acidic, and the pH in the small intestine is close to neutral