Enzymes

• Enzymes are proteins that catalyse chemical reactions in living things. 

  They often contain co-factors, which are usually small organic molecules or metal ions.
• Enzymes have a stereospecific nature, meaning they only react with specific substrates that are complementary to them.
• The enzyme active site is where the catalytic activity takes place. Enzymes have a definite shape, which contains a hollow, due to the tertiary structure. Only molecules that exactly fit this shape will fit into the hollow or active site.
• The 'lock and key' mechanism:

  • The substrate, like a key, must fit exactly in the lock, the active site.
  • Within this hollow there are amino acid residue R groups, these interact with the substrate holding it in place. The complementary substrate is broken down into its products.
  • The activation energy is lowered because the bonds in the substrate are weakened.
• Due to the stereospecific nature, enzymes only catalyse one enantiomer of optical isomers. This is one way chemists can synthesise just one of the enantiomers in chiral drug synthesis – avoiding undesirable side effects.
• Inhibitors:

  There are molecules with a similar shape to the substrate, they compete with the substrate for the enzyme active site. The inhibitors block the active site, preventing the substrate from binding, therefore no reaction follows.

  • High concentration of inhibitor to substrate = Fewer substrates gets to the active site and broken down into products.
  • Low concentration of inhibitor to substrate = More substrate gets to the active site and broken down.