1.4

• Metabolism


  A series of enzyme-controlled reactions in the body
• Main types of metabolism reactions


  • Building up reactions (anabolic reactions or anabolism)
  • Breaking down reactions (catabolic reactions or catabolism)
• Anabolic reaction


  Protein synthesis where amino acids are built up into more complex polypeptides
• Catabolic reaction


  Digestion of proteins, where complex polypeptides are broken down into simple amino acids
• Enzymes


  • They are proteins that speed up chemical reactions
  • They lower the activation energy needed for the reaction to take place
  • They don't actually take part in the reaction
  • They are only needed in small quantities
  • They can be used over and over again
  • They convert substrates into products
• Enzymes


  Biological catalysts
• Primary structure


  Formed from the order of amino acids
• Condensation


  Reaction occurs joining two molecules together into a larger one with the elimination of water
• Secondary structure


  Formed from the folding of the primary structure into two main forms: the alpha helix or beta pleated sheet
• Tertiary structure


  Formed from the folding of the secondary structure into a 3D shape
• Hydrolysis


  The breaking down of large molecules into smaller ones by the addition of a molecule of water
• Enzyme catalysis in catabolic reactions


  1. Substrate binding

  2. Reaction proceeds

  3. Products released

  4. Active site free to catalyse another reaction
• Enzyme catalysis in anabolic reactions


  1. Several substrates bind

  2. One or more products released
• Activation energy


  Energy needed to start a reaction
• Enzymes


  Lower the activation energy needed to start a reaction
• Enzymes may act intracellularly (within a cell) or extracellularly (outside a cell)
• Lock and key model


  Substrate has a complementary shape to the enzyme's active site
• Induced fit model


  Active site is able to change slightly to accommodate the substrate
• Induced fit model explains why several molecules with similar shapes can bind to the active site
• Factors affecting the rate of enzyme action


  • Substrate concentration
  • Temperature
  • pH
  • Enzyme concentration
  • Presence of inhibitors
• Increasing substrate concentration


  Increases chance of successful collision between enzyme and substrate, increasing rate of reaction
• Increasing temperature


  Increases rate of reaction up to an optimum, then decreases due to denaturing
• Increasing/decreasing pH from optimum

  Decreases rate of reaction
• Increasing enzyme concentration


  Increases chance of successful collision between enzyme and substrate, increasing rate of reaction
• Competitive inhibition


  Inhibitor has similar shape to substrate and binds to active site
• Non-competitive inhibition


  Inhibitor binds to another site on enzyme, changing shape of active site
• Immobilised enzymes


  • Enzymes fixed to an inert matrix by entrapment or micro-encapsulation
  • Advantages: enzyme can be easily recovered and reused, product not contaminated, more stable at higher temperature, can catalyse reactions in a wider range of pH
• Biosensors


  Contain immobilised enzymes to detect small concentrations of specific molecules in a mixture