Enzymes (T2aY9)

• the active site is the part of an enzyme where substrate molecules bind to form an enzyme-substrate complex
• enzymes are biological catalysts that speed up chemical reactions
• an enzyme-substrate complex is formed when the substrate molecule fits into the active site of the enzyme, forming temporary bonds between them.
• an enzyme has a specific shape which allows it to fit together with its substrates, forming an enzyme-substrate complex
• Enzymes


  Biological catalysts
• Enzymes


  • Their role in cells is to speed up reactions inside cells
  • They are made by cells and speed up reactions, but are not used up
• Enzyme


  Protein molecule, made of long chains of amino acids
• Enzyme


  • They have a 'dent' (cleft) called the active site
  • A substrate to be broken down fits into this
  • This is where the reaction takes place and the product is made
  • Only 1 substrate will fit into the active site (like one key fits into a lock) so enzymes are specific in what they break down
• Types of enzyme-catalysed reactions

  • Break down reactions (e.g. digestion of starch or respiration)
  • Build up reactions (e.g. photosynthesis)
• If the active site changes shape


  The substrate cannot fit into it, so the enzyme can no longer function
• Denatured enzyme


  When the active site of the enzyme changes shape, so the substrate doesn't fit in properly
• Factors that denature enzymes

  • High temperatures
  • Extremes of pH (acids and alkali)
• Factors that affect the rate of an enzyme-catalysed reaction

  • Temperature (increases up to about 40 C, then decreases as the enzyme denatures)
  • Enzyme Concentration (the rate increases as enzyme conc. increases, up to a maximum rate)
  • Substrate Concentration (similarly affects the rate)
• At lower temperatures


  Enzymes and substrates have less kinetic energy, so there are fewer collisions between them, so the rate of reaction is low
• If an enzyme gets too hot

  It denatures, meaning the active site's shape changes, so the substrate can no longer bond, so the rate of reaction is low
• Enzymes


  • Amylase (breaks down starch into sugars)
  • Lipase (breaks down lipids (fats) into fatty acids and glycerol)
  • Protease (breaks down proteins into amino acids)
• The enzyme amylase works best at pH 7 (as this the pH of the mouth)
• Investigating an enzyme reaction

  • We must change only ONE of the factors that can affect enzyme action (temperature, pH, enzyme concentration and substrate concentration) – so we are doing a valid experiment (it is a fair test)
• Independent variable


  The variable we deliberately change
• Control variables


  The other factors (variables) which can affect the rate of enzyme action that we keep the same
• Dependent variable


  What we measure
• Measuring the rate of amylase action

  1. Using a petri dish which contains agar jelly mixed with starch solution

  2. Iodine is also added to the agar, which means the agar goes blue / black

  3. Small wells are made in the agar and the enzyme amylase is added

  4. As the amylase in each well digests the starch, we see clear zones around each well

  5. The wider the diameter of the clear zones, the faster the rate of amylase action
• Catalysts


  Chemicals that speed up reactions
• Biological catalysts


  Enzymes that speed up biological reactions, such as digestion
• Enzyme catalysed reaction

  1. substrate

  2. products

  3. protein

  4. amino acids
• Extracellular enzymes


  Enzymes that digest food in the gut cavity, outside of cells
• Intracellular enzymes


  Enzymes that work inside cells, e.g. controlling respiration
• Enzymes

  Protein molecules (chains of amino acids)
• Active site


  The dent in an enzyme where the molecule it will break down fits into
• Lock and key model


  Model of enzyme action where the substrate fits into the active site
• Denatured


  When an enzyme changes shape and stops working, usually due to heat
• As temperature increases

  Particles gain kinetic energy, so move faster and collide more
• Optimum temperature


  The temperature at which the reaction is fastest
• As temperature increases further

  The enzyme denatures, the active site changes shape, so the substrate won't fit
• Other factors that can cause enzyme denaturation

  • Extremes of pH (strong acid and alkali)
• Factors that affect enzyme activity

  • Temperature
  • pH
  • Enzyme concentration
  • Substrate concentration
• Dependent variable


  The variable that is measured in an experiment
• Independent variable


  The variable that is deliberately changed in an experiment
• Control variables


  Variables that are kept the same in an experiment
• To find how pH affects the rate of amylase activity, we can measure how quickly the starch is used up