Enzymes & digestion

• catalyst


  a substance which increases the speed of reaction without being changed or used up
• induced fit theory


  the active site changes slightly to fit the substrate
• lock & key theory


  every enzyme has an active site with a unique shape that fits onto the substrate involved in a reaction.
• enzymes need the right temperature and ph to work optimally
• enzymes usually work best at pH 7 but not all. enzymes such as pepsin in the stomach work best at pH 2
• rate of reaction =

  1000/time
• time =


  1000/rate of reaction
• digestive enzymes break down big molecules
• starch, fats and proteins are too big to pass through body so they are broken down into smaller molecules
• enzymes are known as biological catalysts
• starch


  amylase enzyme breaks down starch into maltose
• amylase is produced in

  • salivary glands
  • the pancreas
  • small intestine
• Proteins


  protease enzyme breaks down proteins into amino acids
• proteins are produced in

  • stomach
  • pancreas
  • small intestine
• Lipids


  lipase enzymes break dow lipids into glycerol and fatty acids
• lipids are produced in

  • pancrease
  • small intestine
• bile


  neutralises the stomach acid and emulsifies fats
• bile is produced in

  the liver
• bile is stored in

  the gall bladder before being released into the small intestine
• the hydrochloric acid in the stomach makes the pH acidic
• the hydrochloric acid in the stomach makes the pH too acidic for the enzymes in the small intestine to work properly. bile is alkaline - it neutralises the acids
• salivary glands


  produce enzymes in the saliva
• liver


  where bile is produced. bile neutralises stomach acid and emulsifiers fats
• stomach


  pummels food with its muscular walls

  produces protease, enzyme, pepsin

  produces hydrochloric acid to kill bacteria and give the right pH for protease enzyme to work
• gall bladder


  where bile is stored before it is released into small intestine
• pancreas


  produces protease, amylase and lipase enzymes. it releases these into the small intestine
• large intestine


  where excess water is absorbed from the food
• small intestine


  produces protease, amylase and lipase enzymes to complete digestion.