Enzymes

• What is metabolism?


  The sum of all the enzyme controlled chemical reactions taking place in a cell.
• What are the two main types of reactions that make up metabolism?


  Anabolic and catabolic reactions.
• What is anabolism?


  A set of metabolic pathways that synthesise complex molecules from smaller, simpler molecules.
• What is catabolism?


  A set of metabolic pathways that breakdown complex molecules into smaller, simpler molecules.
• What is an enzyme?


  A biological catalyst used to speed up the rate of intracellular and extracellular biochemical reactions without being used up or permanently altered.
• What is an intracellular enzyme?


  An enzyme that acts within cells e.g. catalase.
• What is an extracellular enzyme?


  An enzyme that is secreted by cells and functions outside of cells e.g. amylase.
• What is the active site of an enzyme?


  A region on an enzyme that is complementary to the shape of a specific substrate. The substrate binds and the reaction takes place.
• Why is an active site described as 'specific'?


  Only specific substrates complementary to the active site can bind
• What is activation energy?


  The minimum amount of energy required for a reaction to take place.
• What is catalysis?


  An increase in the rate of a chemical reaction using a catalyst (such as an enzyme)

  The catalyst lowers the activation energy of the reaction.
• Describe the 'lock and key' model


  Substrate and the active site of the enzyme come into contact

  Substrate binds and enzyme-substrate complex forms

  Reaction takes place and a product is formed in an enzyme-product complex

  Product is released from the active site, so it is now free to bind to another substrate
• What is the induced-fit hypothesis?


  A model of enzyme action which states that once a specific substrate binds to the active site, the enzyme undergoes subtle conformational changes. This puts a strain on the substrate, lowering the activation energy for the reaction.
• What factors affect the rate of an enzyme-controlled reaction?


  Temperature, pH, substrate concentration, enzyme concentration
• How does temperature affect the rate of enzyme-controlled reactions?


  As temperature increases molecules have more kinetic energy

  Molecules move faster and collide more frequently

  More enzyme-substrate complexes form

  Rate of reaction increases
• How does increasing temperature above the optimum affect the rate of an enzyme-controlled reaction?


  Increased vibrations break hydrogen and ionic bonds in tertiary structure

  Active site changes shape, enzyme is denatured

  No more enzyme-substrate complexes can form

  Rate of reaction decreases
• How does pH affect the rate of enzyme-controlled reactions?


  Hydrogen and ionic bonds in the tertiary structure are altered

  Interaction of polar and charged R groups changes

  Active site changes shape, enzyme is denatured

  Rate of reaction decreases
• What is a buffer?


  A molecule that maintains a constant pH in a solution when small volumes of acid or base are added.
• How does substrate concentration affect the rate of an enzyme-controlled reaction?


  If enzyme concentration is fixed, the rate of reaction increases proportionally to the substrate concentration

  Once all active sites become full, the rate of reaction remains constant (graph plateaus)
• How does enzyme concentration affect enzyme activity?


  If substrate concentration is fixed, the rate of reaction increases proportionally to the enzyme concentration

  When all of the substrates occupy active sites, the rate of reaction plateaus
• What is a competitive inhibitor?


  A molecule which competed for the active site of an enzyme, blocking it and preventing the substrate from binding.
• Is competitive inhibition temporary or permanent?


  It is generally temporary, but in some cases (e.g. aspirin) it may be permanent.
• How does increasing substrate concentration affect competitive inhibition?


  Increase in substrate concentration

  More substrate than inhibitor

  Rate of reaction increases
• What is a non-competitive inhibitor?


  An inhibitor which binds to a different part of an enzyme, the allosteric site

  The tertiary structure of the enzyme (including the active site) changes shape

  The active site is no longer complementary to the substrate

  The substrate cannot bind and the enzyme is inhibited
• Is non-competitive inhibition temporary or permanent?


  Permanent
• How does increasing substrate concentration affect non-competitive inhibition?


  There is no effect.
• What are immobilised enzymes?


  Enzymes which are attached to an inert, insoluble material over which the substrate passes and the reaction takes place.
• What is an example of an application of immobilised enzymes?


  Biosensors
• Why are immobilised enzymes important in industrial processes?


  Enables enzymes to be reused

  Improves enzyme stability in variable/extreme temperatures and pH

  Increases the efficiency of reactions