enzymes

• Enzymes increase the rate of reaction by lowering the activation energy of the reaction they catalyse
• Active site is the area of the enzyme where the reaction with the substrate takes place
• Enzymes are specific to substrates they bind to, meaning that only one type of substrate fits into the active site of the enzyme
• When the enzyme and substrate form a complex, the structure of the enzyme is altered so that the active site of the enzyme fits around the substrate. This is called the induced fit model
• • Temperature: rate of reaction increases up to the optimum temperature, then decreases above the optimum temperature
• Factors affecting the rate of enzyme-controlled reactions:

  • Enzyme concentration: rate of reaction increases as enzyme concentration increases, more active sites for substrates to bind to. Beyond a certain point, no effect on the rate of reaction as substrate concentration becomes the limiting factor
  • Substrate concentration: rate of reaction increases as substrate concentration increases, more enzyme-substrate complexes formed. Beyond a certain point, rate of reaction no longer increases as enzyme concentration becomes the limiting factor
• Inhibitors:

  • Inhibitor is a substance that slows down or stops a reaction by affecting the binding of substrate to the enzymes
  • Inhibitors can be reversible or irreversible
  • Irreversible inhibitors include heavy metal ions like mercury and silver, and cyanide
  • Reversible inhibitors bind to the active site through hydrogen bonds and weak ionic interactions, can be competitive or non-competitive
  • Competitive inhibitors bind to the active site of the enzyme, decreasing its activity as they compete with substrate
• • Non-competitive inhibitors bind at another site on the enzyme known as the allosteric site, changing the shape of the active site
  • Many drugs are inhibitors, examples include penicillin and Ritonavir
• Coenzymes:

  • Cofactor is a non-protein compound required for the enzyme’s activity to occur
  • Coenzymes are organic cofactors which do not bind permanently, facilitate the binding of substrate to enzyme
  • Examples of coenzymes include NAD derived from niacin
  • Activators are inorganic metal ions that temporarily bind to the enzyme and alter its active site
  • Prosthetic groups are permanently attached to the enzyme, for instance, haemoglobin contains a prosthetic haem group