biology chapter 4

Cards (22)

  • 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