Enzymes

enzyme - a globular protein that acts as a biological catalyst, by lowering the activation energy to speed up the rate of a reaction

• enzymes have a specific tertiary structure, so the active site will have a unique structure
  • thus, enzymes are specific and onlty catalyse one reaction, with the complementary structured substrate
• the active site is where the substrate binds and the reaction takes place
  • r-groups will bind the to substrate to form an ESC (enzyme-substrate complex)

• enzymes speed up the rate of reaction by lowering the activation energy
  • this is the energy required to start a reaction
• this allows for reactions that wouldn't normally occur to take place

Lock and Key:

• this argues that the enzmye and substrate are 100% complementary to each other
• however, it does not explain;
  • how the AE is lowered
  • inhibitors

Induced Fit:

• the active site is not 100% complementary and the enzyme has to change shape
• bonds form between the substrate and the r-group
  • strain is put on the substrate and the bond is broken

• an increase in temperature will
  • give the molescules more kinetic energy
  • creates more successful collisions
  • more ESCs are formed
• an increase that is too high will
  • cause vibrations that breaks the hydrogen and ionic bonds
  • this changes the shape of the active site and the enzyme denatures

• H+ ions are attracted to the negative r-groups
  • this reduces the ability for the substrate to bind to the active site
• the tertiary shape will change as the bonds break and the substrate is no longer complementary

• an inscrease will
  • cause a greater chance in the substrate and the active site meeting
  • thus, more successful collisions will occur
  • there must, however, be an excess of substrate for this to happen

• an increase will
  • increase the chance of the active site and the substrate meeting, so more successful collisions can happen
• eventually, it is the enzyme concentration that will become the limiting factor

• a competitive inhibitor has a similar shape to the substarte and is thus complementary to the active site
• it enters the active site, preventing the substrate from binding to ut
  • the collisions are less successful
  • less ESCs are formed
• this is reversible and the inhibitor can be knocked out with an excess of substrate
  • therefore, the end maximum is not effected, but the rate of reaction is slowed down

• non-competitive inhibitors bind to the allosteric site of the enzyme
  • this causes a change in the tertiary structure
  • the active site thus becomes distorted
  • the substrate no longer fits and the enzyme is denatured
• this is irriversible
  • the maximum is greatly reduced