biology chapter 4

• enzymes are globular proteins that catalyse reactions in living organisms, they have an active site
• how activation energy is lowered:

  • if two substrate molecules need to be joined the enzyme holds them together so they can bond more easily
  • if the ezyme is catalysing a breakdown, fitting into the active site puts a strain on the bonds of the substrate so they can be broken more easily
• induced fit model:

  • active site is not complementary
  • active site is flexible, changes shape so substrate can bind to it
  • E-S complex forms
• lock and key model:

  • active site is complementary
  • active site is a fixed shape
  • active site doesn't wrap around substrate
• factors affecting enzyme activity - temperature:

  • higher temperature = faster rate of reaction
  • more kinetic energy for molecules so they move faster
  • more frequent successful collisions between active site and substrate

  
• enzymes become inactive at low temperatures, and denatured at high temperatures
• factors affecting enzyme activity - pH:

  • affects ionic and hydrogen bonds
  • protons interact with polar and charged amino acids
  • higher pH = increase in enzyme activity, until it reaches the optimum pH

  
• factors affecting enzyme activity - substrate/enzyme concentration:

  • higher substrate concentration increases rate
  • higher enzyme concentration increases rate
• factors affecting enzyme activity - enzyme concentration:

  • higher enzyme concentration increases rate as there are more active sites available
  • rate stops increasing when there is not enough substrate to occupy all the active sites

  
• factors affecting enzyme activity - substrate concentration:

  • higher substrate concentration increases rate
  • the rate stops increasing when all the active sites are occupied

  
• competitive inhibition:

  • Ic have a similar structure to S (substrate)
  • Ic competes with S for the same active site
  • higher substrate concentration means that S can out-compete Ic and restore Vmax

  
• non-competitive inhibition:

  • In binds to allostenic site
  • changes to 3D structure of active site, the active site is no longer complementary to S
  • higher substrate concentration cannot restore Vmax

  
• equation for Q10:

  A) higher

  B) lower

  
• cofactor: a non-protein component that helps some enzymes carry out their function.
• a coenzyme is an organic cofactor
• coenzymes (organic cofactors):

  • participate in the reaction and are changed by it
  • they often act as carriers moving chemical groups between enzymes
  • they are continually recycled during the process
  • vitamins are coenzymes
• prosthetic groups:

  • a cofactor that is tightly bound to an enzyme
  • they are a permanent part of the enzyme's active site
• competitive inhibitors:

  • similar shape to substrate
  • they bind to the active site but no reaction takes place, instead the active site is blocked
• non-competitive inhibitors:

  • the bind to a different site to the active site, called the allosteric site
  • causes the active site to change shape so that substrate molecules can no longer fit and bind to it
• V-max: the enzyme's active sites are saturated, so the rate of reaction will not increase further
• reversible inhibition:

  • forms weaker hydrogen bonds or weak ionic bonds
  • the inhibitor can be removed
• non-reversible inhibition:

  • forms strong covalent bonds
  • the inhibitor cannot be removed easily