Enzymes

• what are enzymes?


  biological catalyst made of globular protiens
• the active site is specific and unique in shape due to specific folding and bonding in the tertiary structure of the protein and they have a complementary in shape
• enzymes catalyse intracellular and extracellular reactions
• optimum conditions for an enzyme reaction are when there is maximum rate of reaction with minimum energy input from the environment (lowest activation energy)
• enzyme activity can be affected by temperature, pH, substrate concentration and inhibitors
• all reactions require a certain amount of energy before they occur, this is known as the activation energy
• when enzymes attach to the substrate they can lower the activation energy
• lock and key model

  This model suggest that the enzyme is like a lock and that the substrate is like a key and the enzyme has a specific tertiary structure resulting in a complementary enzyme/substrate complex

  
• induced fit = enzyme active site is induced

  when the enzyme-substrate complex occurs it puts strain on the bonds and therefore lowers the activation energy
• induced fit model

  
• factors affecting enzymes

  • temperature
  • pH
  • enzyme concentration
  • substrate concentration
• what happens if the temperature is too high?


  the enzymes denature and the active sites changes and enzyme complexes can not form

  • causes tertiary structure to alter causing a change in shape of active site
• what happens if the pH is too high or low?


  this can interfere with the charges in the amino acids in the active sites

  • causes hydrogen and ionic bonds to break
  • alter tertiary structure and changes the shape of the active site and enzymes denature
• what effect does enzyme and substrate concentration have?

  • with lower substrate concentration fewer collisions between the enzyme and substrate
  • increasing the substrate concentration will increase the rate of reaction because all the active sites are being used
• competitive inhibitors

  • same shape as the substrate and complementary in shape to active site therefore bind to the active site
  • this prevents the substrate from binding
  • most are reversible
• Non competitive

  • binds to the allosteric site which cause the active site to change
  • substrate can bind until inhibitors leave the allosteric site
• End product Inhibition

  • the product of some reaction are reversible inhibitors for the enzymes involved in controlling the reaction
  • enables the reaction to be controlled
  • prevents resources from being wasted
• coenzymes and cofactors

  • non protein molecules that bind to the active site to make it complementary to the substrate
• Prosthetic groups are a type of cofactor that are permanently attached to the enzyme by covalent or non covalent bonds
• precursor activation

  • enzymes often occur in an inactive form and require activation by a co factor
  • this prevents enzymes from causing damage within cells and ensure they are only used when they are needed