3.6

• Digestion


  The breakdown of large insoluble molecules into soluble substances that can be absorbed into the blood across the wall of the small intestine
• Digestive enzymes


  • Produced by specialised cells in glands and in the lining of the digestive system
  • Work outside the cells
• Carbohydrases


  Enzymes that break down carbohydrates
• Amylase


  Enzyme that breaks down starch into sugars
• Digestion of starch


  1. Starts in the mouth with amylase from salivary glands

  2. Continues in the small intestine with amylase from the pancreas
• Proteases


  Enzymes that break down proteins into amino acids
• Digestion of proteins


  Occurs in the stomach and small intestine
• Lipases


  Enzymes that break down lipids (fats and oils) into fatty acids and glycerol
• Digestion of lipids


  Occurs in the small intestine
• Once food molecules are completely digested, they leave the small intestine and pass into the bloodstream to be carried around the body
• Alexis St Martin's gunshot wound in 1822 allowed Dr William Beaumont to study digestion in the stomach
• Investigation of the effect of pH on the rate of amylase-catalysed reaction

  1. Prepare starch solutions at different pH

  2. Add amylase

  3. Take samples over time and test with iodine

  4. Observe and record results
• Amylase, starch, and iodine


  Used in the investigation to observe the breakdown of starch
• Concentration and volume of starch solutions and enzyme must be known and the same
• Test solutions kept in a water bath below 37°C to control temperature
• Spotting tiles with iodine


  Used to test for presence of starch in samples
• Pipettes must be rinsed with clean water between samples
• If all starch is broken down before first sample or no starch is broken down after an hour, it would be hard to get useful results
• Three types of enzymes in the body

  • Amylase
  • Protease
  • Lipase
• Amylase


  Breaks down carbohydrates
• Protease


  Breaks down proteins
• Lipase


  Breaks down lipids
• Where each enzyme reaction occurs in the digestive system

  1. Amylase: mouth and small intestine

  2. Protease: stomach and small intestine

  3. Lipase: small intestine
• Pepsin


  Works best at low pH in the stomach
• Pancreatic amylase


  Works best at alkaline pH in the small intestine
• As pH increases


  Enzyme activity decreases
• Enzymes have optimal pH ranges where they work most efficiently
• Digestion of food is important to break down large insoluble molecules into smaller soluble molecules that can be absorbed and used by the body's cells