enzymes

• all enzymes are proteins
• most enzymes are very large molecules but only a small part of them, the ACTIVE SITE, is involved in catalysis
• the active site is stereospecific
• this means it binds/reacts with only 1 particular stereoisomer
• the remainder of the amino acids maintain the precise shape of the enzyme and the active site
• A&B are a pair of enantiomers -> non-superimposable mirror images
• despite having the same shape, B doesn't fit in the stereospecific active site of the enzyme, therefore, B is not stereospecific to the active site
• A fits in the stereospecific active site of the enzyme as A is stereospecific to the enzyme
• the active site of an enzyme binds the substrate molecules of a biochemical reaction, and is critical to its specificity and catalytic activity
• physical, e.g. temperature, or chemical, e.g. pH, factors can break the secondary and tertiary structure
• if the secondary or tertiary structure of the enzyme are affected, the active site will be changed and this will affect the catalytic activity of the enzyme
• enzyme inhibition

  • molecules that have a similar shape to the active site can compete with the reactant molecule to bond to the active site - called enzyme inhibitors
  • when this happens, the active site is blocked by the enzyme inhibitor and the reactant molecule cannot bond - catalysis will NOT happen at this blocked active site
  • the amount of inhibition depends upon the relative concentration of reactant and inhibitor
  • the greater the amount of inhibitor, the more active sites will be blocked
  • the amount of inhibitions depends on how strongly the inhibitor bonds to the active site
• why use enzyme inhibition?

  some antibiotics block the active site of an enzyme in bacteria which causes the cell wall to weaken and her time, the bacteria bursts
• how do we develop enzyme inhibitors?

  • takes a lot of effort to develop a drug that fits into a stereospecific active site, often by trial and error
  • computers are used to model the shape of the enzyme active site and predict how well potential drugs will bind with the active site