Enzymes

• Enzymes


  Proteins which act as Biological Catalysts
• Enzymes


  • They speed up chemical reactions which go on inside living things
  • Without them the chemical reactions vital to life could not take place quickly enough
• Catabolic enzymes


  Break down large molecules into smaller ones, e.g. in digestion
• Anabolic enzymes


  Build up large molecules from smaller ones, e.g. in photosynthesis
• Enzymes, like other proteins, are made inside cells
• Types of enzymes


  • Extracellular enzymes (exert action outside of the cell, e.g. digestive enzymes)
  • Intracellular enzymes (exert action within the cell, e.g. for growth and repair)
• Enzymes can control where and when chemical reactions take place
• Enzyme name


  Usually comes from the name of the substance on which it acts with the ending changed to -ase
• Substrate


  The substance which the enzyme acts upon
• Product


  The new substance(s) formed after the enzyme acts on the substrate
• Enzymes are not used up in the reaction and can be reused
• Product


  New substance(s) formed in a reaction
• Enzymes


  Not used up in the reaction and can be reused
• Substrates and enzymes


  • Substrate
  • Enzyme
  • Protein
  • Protease
  • Lipid
  • Lipase
  • Carbohydrate
  • Product
  • Amino acids
  • Carbohydrase/amylase
  • Fatty acids/Glycerol
  • Glucose
• The Effect of Amylase on Starch-CATABOLIC REACTION


  1. Introduction

  2. Starch is a large insoluble molecule which needs to be digested before absorption can take place

  3. Amylase is an enzyme found in saliva which digests starch

  4. Apparatus

  5. Spotting plate, 200ml syringe, starch solution, amylase, stop clock, iodine

  6. Results

  7. Before you start

  8. Method

  9. Place a few drops of iodine in each dimple of a spotting plate

  10. Take up 10 ml of starch solution into the syringe

  11. Rinse the outside of the syringe with water

  12. Put one drop of starch solution from the syringe into the first dimple of iodine in the spotting plate

  13. Note the colour as a record of time 0 seconds

  14. Take up some of the amylase solution into the same syringe and start the clock

  15. Gently invert the syringe to mix the contents

  16. At 30 seconds on the clock, add another drop from the syringe of the now starch-amylase mixture to the next drop of iodine in the spotting plate

  17. Note the colour change at 30 seconds

  18. 10. Repeat adding drops from the syringe at 30 second intervals until all the drops of iodine are used or until no colour change is observed
• Once the practical is completed, make a conclusion about the effect that amylase has on starch
• Catabolic reaction


  Reaction that breaks down larger molecules into smaller ones
• Amylase


  A carbohydrase enzyme that digests starch
• Starch is an insoluble molecule that needs to be digested before absorption can take place
• Amylase is an enzyme found in saliva that digests starch
• The amylase effects the digestion of the insoluble starch, changing it into more soluble sugar over time
• Enzyme


  Has a 3-D structure with an active site that a specific substrate fits into, like a key in a lock
• An enzyme which digests carbohydrate will not be able to digest protein and vice versa
• Experiment to demonstrate the specificity of enzymes

  • Starch and Amylase
  • Starch and Lipase
  • Starch and Protease
• The colour with iodine changes over 10 minutes for the different enzyme-substrate combinations, demonstrating enzyme specificity
• Color change in iodine

  Indicates the presence or absence of starch, allowing observation of the effect of amylase on starch
• Spotting plate, 200ml syringe, starch solution, amylase, stop clock, iodine


  Apparatus needed to observe the effect of amylase on starch
• Amylase


  Enzyme found in saliva that catalyzes the breakdown of starch
• Starch


  Large, insoluble molecule that must be broken down before it can be absorbed by the body
• Molecules


  • Have kinetic energy and are constantly moving about and bumping into each other
• Enzyme catalysis


  1. Substrate molecule bumps into a molecule of the right enzyme

  2. Substrate fits precisely with the active site

  3. Reaction takes place

  4. Products leave the active site

  5. Enzyme is unchanged and can be used for another substrate molecule
• Factors affecting enzyme activity

  • Temperature
  • pH
  • Concentration of enzyme
  • Enzyme inhibitors
• Effect of temperature on enzyme activity

  1. As temperature increases, molecules gain more kinetic energy and can move about faster

  2. Increasing the frequency of collisions between enzyme and substrate

  3. Rate of reaction increases until an optimum temperature is reached

  4. Rate of reaction is at its highest at the optimum temperature
• The shape of the graph showing the effect of temperature on enzyme activity is not symmetrical
• Denaturation


  The high temperature affects the shape of the enzyme and it is said to be denatured
• When an enzyme is denatured (destroyed) by heat

  The shape of the active site is altered so that the substrate no longer fits
• Denaturation is irreversible and enzyme action stops
• Low temperatures cause a reduced rate of collisions but the enzyme is not denatured
• Optimum pH


  Enzymes will work best at an optimum pH
• Making an enzyme too acidic or too alkaline can also change the shape of the molecule resulting in the enzyme active site being denatured