4. enzymes

• enzyme

  • enzymes are proteins that function as biological catalysts. they catalyse the rate of chemical reactions. they remain chemically unchanged at the end of the reaction.
• catalyst

  a substance that can speed up a chemical reaction without itself being chemically changed at the end of the reaction
• lock-and-key hypothesis

  • how an enzyme will only act on a specific substrate
• mode of action of an enzyme

  1. when a specific substrate binds to an enzyme's active site as the shapes are complementary, an enzyme-substrate complex is formed
  2. chemical reactions take place at the active site to convert the substrate molecules into product molecules
  3. the product molecules will separate from the enzyme.
  4. the enzyme remains chemically unchanged and the active site is available for other substrate molecules to bind to it
• characteristics of enzymes

  • speed up chemical reactions
  • specific in action
  • required in small amounts and remain chemically unchanged at the end of the reaction.
  • affected by temperature & pH
• enzymes are specific in action

  • only a substrate that has a complementary to the enzyme's active site will be able to bind with the enzyme and cause a chemical reaction
• enzymes are required in small amounts and remain chemically unchanged at the end of a reaction

  • once the products leave, the enzyme's active site is free to bind to another substrate molecule.
  • a small amount of enzyme can catalyse the reaction for a large amount of substrate
• enzymes are affected by temperature

  1. an enzyme is less active at low temperatures. the kinetic energy of molecules is low. chances of effective collision between enzyme and substrate molecules is very low.
  2. as the temperature increases, the rate of enzyme reaction increases.
  3. at optimum temperature, the enzyme activity is the fastest.
  4. as temperature increases above optimum temperature, the enzyme starts to denature. rate of reaction will decrease rapidly and the active site will begin to lose its original shape.