• tertiary globular proteins
  • protein chain folded back on itself into spherical or globular shape
  • own sequence of amino acids
  • held in tertiary form by hydrogen bonds, disulphide bridges and ionic bonds
  • complex 3D shape
  • large molecule but only active site is functional

How they work

  • biological catalysts that speed up metabolic reactions
  • large molecules broken down into smaller molecules
  • smaller molecules built up into larger, more complex molecules
  • react with a substrate

Enzyme + substrate ----> enzymes-substrate complex ----> enzyme + product


  • specific - each enzyme will catalase only one particular reaction, e.g. sucrase acts on sucrose
  • very efficient and have high turnover number - can convert many molecules of substrate per unit time, e.g. catalase which breaks down the waste product hydrogen peroxide in the body has a turnover of several million
  • chemical reactions need energy to start them (activation energy). Needed to break existing chemical bonds inside molecules. Enzymes lower activation energy of a reaction reducing the input energy needed and allowing reactions to occur at lower temperatures


  • made inside living cells but may act inside (intracellular) or outside (extracellular) a cell
  • environmental conditions, e.g. temperature and pH change 3D structure of enzyme molecules. Bonds are broken and the configuration of the active site is altered


  • increase in temp increase kinetic energy so they move around…


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