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  1. Enzymes D. Crowley, 2007

  2. Enzymes • To know how enzymes work, and their importance

  3. Food Test • Can you remember the tests for food? • Fat test • Simple sugar test • Starch test • Protein test Rub food onto paper - if fat is present, it will leave a translucent stain Benedicts solution, in a water bath - orange precipitate will form if simple sugars are present Iodine will go from brown, to blue / black in presence of starch Biuret test - solution will go from pale blue to purple in presence of protein

  4. Enzymes • What are enzymes? Why are they so important? • During digestion our teeth break food down into small pieces. However, these chewed pieces of food are still too large to be absorbed by the body. • Food has to be broken down chemically into really small particles before it can be absorbed. Some foods can be absorbed (like simple sugar, vitamins, minerals and water) as they are small enough already. Foods such as starch, protein and fat are too big though, and rely on enzymes to break them down • Enzymes are needed so that this break-down happens quickly enough to be useful. • Digestive enzymes cannot break down fibre, which is why it cannot be absorbed by the body

  5. Enzymes • Enzymes are not living! They are special proteins which can break large molecules down. • There are specific enzymes, which break down specific nutrients: - • Amylase (carbohydrase) enzymes break down starch into simple sugars • Protease enzymes break down proteins into amino acids • Lipase enzymes break down fats into fatty acids and glycerol Anylase - starch to sugar Protease - protein to amino acids Lipase - fats to fatty acids & glycerol

  6. Carbohydrates (amylase enzyme) • Carbohydrates are digested in the mouth, stomach and small intestine. • Amylase is produced in the salivary glands, pancreas, and small intestine. • Chew a piece of bread for long enough, it will taste sweet (as the starch is broken down into simple sugars) amylase carbohydrates  simple sugars

  7. Proteins (protease enzyme) • Proteins are digested in the stomach and small intestine. • Protease is produced in the stomach (called pepsin), pancreas and small intestine. Stomach acid is strong hydrochloric acid, helping digestion and killing harmful micro-organisms that may be in the food. protease protein  amino acids

  8. Fats (lipase enzyme) • Fat is digested in the small intestine. Bile (made in the liver) helps break fat into small droplets that are easier for the lipase enzymes to work on • Lipase is produced in the pancreas and small intestine. lipase fat  fatty acids + glycerol

  9. Absorption • Digested food molecules are absorbed in the small intestine, passing through the wall of the small intestine into the bloodstream (where they are carried around the body to where they are needed). • Only small, soluble substances can pass across the wall of the small intestine. Large insoluble substances cannot pass through - this is why we need enzymes!

  10. Visking Tubing Experiment • It is difficult to do practical work with a real small intestine, however we can model it using visking tubing (a tube with tiny holes in it) • This experiment models the small intestine - only small molecules can pass through the visking tubing, into the boiling tube

  11. Visking Tubing Experiment Experiment: - Take some Visking tubing and tie a knot in one end. Using a syringe, carefully add 5cm3 of starch suspension to the tubing Holding the top of the tubing, wash the outside of it under a tap (to clean off any starch that may have been spilt). Now add 5cm3 of amylase solution Place the tubing inside a boiling tube of water and leave the boiling tube in a warm water bath for 20 minutes. Test the water outside the visking tubing - take one small sample for starch (add a few drops of iodine (blue / black positive result)); and one small sample for simple sugars (add a few drops of Benedicts (orange precipitate positive result))

  12. Visking Tubing Experiment • How could you test to see if the amylase enzyme has broken down the starch? • What should you find? • Remember, iodine can test for the presence of starch (goes blue / black), and Benedicts can test for simple sugars (orange precipitate forms) • Write your predication - this will be assessed, so make sure you include all the scientific details necessary “The water outside the visking tubing (model gut) will contain _________ and will not contain _________. This is because…”

  13. Visking Tubing Experiment • We should find that the boiling tube with warm water contains simple sugars (orange precipitate forms when Benedicts is added); and it does not turn the iodine blue / black • This is because the starch has been broken down into smaller molecules (simple sugars) • Only these molecules are small enough to pass through the visking tubing • Benedicts (simple sugar) should show a positive results - orange precipitate • Iodine (starch) will be negative - remain brown)

  14. Summary Enzymes