Enzymes

• Enzymes


  Proteins that are biological catalysts (speed up chemical reactions)

  
• Enzymes


  • They are necessary to all living organisms as they maintain reaction speeds of all metabolic reactions (all the reactions that keep an organism alive) at a rate that can sustain life
  • They are specific in their action
  • Each enzyme has an area called active site
  • The substrate fits into the active site of the enzyme like the key fitting into a lock

  
• Catalysts


  Chemicals that speed up the rate of a chemical reaction without being changed or used up in the reaction
• Biological


  Made in living cells
• Lock and key hypothesis

  The substrate fits into the active site of the enzyme like the key fitting into a lock

  
• Enzyme action


  1. Substrate moves into enzyme's active site to form enzyme-substrate complex

  2. After reaction, products leave enzyme's active site as they no longer fit it and it is free to take up another substrate
• As temperature increases


  The rate of reaction increases up to a maximum (optimum temperature)
• After optimum temperature


  The enzymes change shape of the active site (denaturing) and the rate of reaction decreases
• As pH increases


  The rate of reaction increases up to a maximum (optimum pH)
• After optimum pH


  The enzyme changes shape and the active site stops being able to bind to the substrate (denaturing)

  
• Optimum pH


  Most enzymes 7, some lower (2) or higher (8-9)
• If pH is too high or too low, the bonds that hold the amino acid chain together to make up the protein can be destroyed, changing the shape of the active site</b>
• Practical: Investigate how enzyme activity can be affected by changes in temperature

  1. Set up water baths at various temperatures

  2. Add starch solution to 5 test tubes

  3. Add amylase solution to 5 test tubes

  4. Place one starch and one amylase test tube into each water bath for 5 minutes

  5. Add amylase to starch, start timer

  6. Every minute remove a sample and add to iodine on spotting tile

  7. Repeat for each temperature

  8. Record results

  9. Draw graph to show time taken for starch to be digested at different temperatures

  
• • At optimum temperature, amylase will break down starch very quickly
  • At low temperatures, amylase will break starch down slowly due to reduced kinetic energy
  • At high temperatures, amylase will break starch down slowly or not at all due to denaturation of the enzyme's active site

  
• Controlled variables: pH, same volume and concentration of starch, same volume and concentration of amylase

  
• Practical: Effect of pH


  1. Place drops of iodine solution in rows on tile

  2. Label test tube with pH to be tested

  3. Add amylase, buffer solution, and starch solution to test tube, start stopwatch

  4. Every 10 seconds, place a drop of mixture on iodine

  5. Repeat at different pH values

  
• The less time the iodine solution takes to remain orange-brown, the quicker all the starch has been digested and so the better the enzyme works at that pH