Cofactors, coenzymes and prosthetic groups

• what is a cofactor?

  a non-protein component necessary for the effective functioning of an enzyme
• what is a coenzyme?

  • substances that must be present to ensure enzyme-controlled reactions take place at an appropriate rate
  • some cofactors are part of enzyme, whilst others affect the enzyme on a temporary basis
  • bind to active site either just before or at the same time the substrate binds
  • are often changed in the reaction, but will be recycled again in subsequent reactions
  • example - Vitamin B3 (nicotinamide)
• what are the roles that the coenzymes NAD and NADP play in metabolism?

  • NAD - used in respiration
  • NADP - used in photosynthesis
  • hydrogen carriers- an organic macromolecule that transports atoms of H from one molecule to another for use in various metabolic processes
  • they are involved in oxidation and reduction reactions
• what are prosthetic groups?

  • organic non-protein groups that are a permanent part of the enzyme molecule
  • contribute to the overall tertiary structure of the protein and its other properties, such as charges
  • without these the overall 3-D shape would change meaning enzyme-substrate complexes can’t form
• what are inorganic ion cofactors?

  • some enzymes require ions that helps stabilise the enzyme-substrate complex
  • the presence (or lack) of these ions will affect charge distribution and possibly tertiary structure
  • the binding of the ion will cause the enzyme-substrate complex to form more easily - therefore increasing reaction rate
• why are some enzymes produced in an inactive form?

  prevents causing damage within the cells producing them or to the tissues where they are released
• how do precursor enzymes be activated by cofactors?

  • before addition of cofactor, precursor protein is called an apoenzyme
  • cofactor is added and the enzyme is activated, it is now called a holoenzyme
  • part of the precursor molecule inhibits its action as an enzyme - once this part is removed the enzyme becomes active
• what is an apoenzyme?

  a precursor protein before the addition of cofactor (before activatio)
• what is a holoenzyme?

  an enzyme after addition of a cofactor (after activation)