5. Enzymes

• Enzymes

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

  • Proteins
  • Biological catalysts (biological because they are made in living cells, catalysts because they speed up the rate of chemical reactions without being changed)
  • 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
• Digestive enzymes

  • Without them, it would take around 2 - 3 weeks to digest one meal; with enzymes, it takes around 4 hours
• How enzymes work

  • Enzymes are specific to one particular substrate (molecule/s that get broken down or joined together in the reaction) as the enzyme is a complementary shape to the substrate
  • The product is made from the substrate(s) and is released
• Enzyme substrate specificity

  
• lock and key method

  
• Investigating the Effect of Temperature on Amylase

  1. Heat starch solution to set temperature

  2. Add iodine to wells of spotting tile

  3. Add amylase to starch solution and mix

  4. Every minute, add droplets of solution to new well of iodine

  5. Continue until iodine stops turning blue-black

  6. Record time taken for reaction to complete

  7. Repeat experiment at different temperatures
• The quicker the reaction is completed


  The faster the enzyme is working
• Investigating the Effect of pH on Amylase


  1. Place single drops of iodine solution in rows on tile

  2. Label test tube with pH to be tested

  3. Use syringe to place 2cm3 amylase in test tube

  4. Add 1cm3 buffer solution to test tube

  5. Add 2cm3 starch solution to amylase and buffer, start stopwatch

  6. Every 10 seconds, place drop of mixture on iodine

  7. Repeat until iodine remains orange-brown

  8. Repeat experiment 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
• rate of temp on enzyme activity

  
• effect of pH on enzyme activity

  
• Enzyme specificity


  Enzymes are specific to one particular substrate(s) as the active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate
• Enzymes

  • They are proteins with a specific 3-D shape
• Lock and key hypothesis

  The shape of the enzyme's active site is complementary to the shape of the substrate
• Enzyme-substrate complex formation

  1. Enzyme and substrate randomly collide

  2. Substrate fits into the enzyme's active site

  3. Reaction occurs
• Enzyme action

  1. Enzyme-substrate complex forms

  2. Products are released from the active site

  3. Enzyme is unchanged and will catalyse further reactions
• Enzymes and substrates randomly move about in solution
• how enzymes work

  
• Enzymes

  Proteins with a specific shape held in place by bonds
• Enzymes

  • The specific shape around the active site area ensures the substrate will fit into the active site and enable the reaction to proceed
• Optimum temperature


  The temperature at which enzymes work fastest - in the human body this is 37⁰C
• Denaturation


  Heating to high temperatures breaks the bonds that hold the enzyme together, causing it to lose its shape
• Denaturation is irreversible - once enzymes are denatured they cannot regain their proper shape and activity will stop
• Increasing temperature from 0⁰C to the optimum

  Increases the activity of enzymes as the more energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction
• Low temperatures do not denature enzymes, they just make them work more slowly
• temperature effect

  
• temprature effect

  
• Optimum pH


  The pH at which an enzyme works best
• Optimum pH for enzymes

  • pH 7
  • pH 2 (for enzymes produced in acidic conditions like the stomach)
  • pH 8 or 9 (for enzymes produced in alkaline conditions like the duodenum)
• If the pH is too high or too low


  The bonds that hold the amino acid chain together to make up the protein can be destroyed
• Bonds that hold the amino acid chain together being destroyed

  Changes the shape of the active site
• Active site shape changing

  Substrate can no longer fit into it, reducing the rate of activity
• Moving too far away from the optimum pH


  Causes the enzyme to denature and activity will stop
• pH effect

  
• temperature effect