Mechanisms of enzyme action

• what is the role of enzymes in metabolism?

  to control and regulate the chemical reaction
• what is lipase produced by?

  • liver
  • bacteria
  • pancreas
• why are enzymes necessary, using maltose as an example?

  • by hydrolysing the covalent (glycosidic) bond between 2 glucose molecules
  • this wont happen naturally as covalent bonds are stable and strong
• what is activation energy?

  the minimum amount of energy that must be applied for a reaction to proceed
• what are the steps of the lock-and-key model?

  • active site is complementary in shape of the substrate, the substrate fits into the active site
  • the substrate is held in place, forming an enzyme-substrate complex so reaction can take place (R-groups interact and strain is put on bonds within substrate)
  • product is released and enzyme is unchanged and is ready to accept another substrate molecule
• what is the induced fit model?

  more recently, evidence from research into enzyme action suggests the active site of the enzyme actually changes shape slightly as the substrate enters - to be perfectly complementary
• what are the steps of the induced fit model?

  • substrate collides with enzyme, enzyme slightly alters shape
  • the strain on the substrate bonds causes the reaction to occur more easily, once the reaction occurs an enzyme-product complex is formed
  • products have different shape to the active site so they no longer fit and move away
• what does adding enzymes to a reaction mean you don’t have to do?

  increase temperature
• what does more strain on substrate bonds cause?

  lowered activation energy
• what is the now accepted enzyme model?

  Induced fit model
• what is a substrate?

  a substance that binds to the active site, used up in an enzyme-controlled reaction
• what is an enzyme-substrate complex?

  intermediate structure formed when a substrate molecule binds to an enzyme molecule
• what are the similarities of the lock-and-key model and the induced fit model?

  • both put strain on the bonds within the substrate to lower the activation energy
  • enzyme-substrate complex is formed
  • enzyme remains unchanged
  • enzymes have an active site
• what are the differences between the lock-and-key model and the induced fit model?

  • LAK has an active site which is exactly complementary in shape
  • LAK doesn’t explain why the activation energy is lowered - Induced fit has an active site which is almost complementary in shape, it changes to fit, explains why the activation energy is lowered and puts strain on the substrate
• describe the digestion of starch

  • amylase breaks down starch polymers into maltose
  • amylase in produced in the salivary glands and the pancreas
  • maltase breaks maltose down into glucose
  • maltase produced into the small intestine
  • glucose is small enough to be absorbed by the cells lining the digestive system and subsequently into bloodstream
• describe the digestion of protein

  • trypsin breaks down proteins into smaller peptides
  • trypsin is produced in the pancreas
  • other proteases breaks down smaller peptides into amino acids
  • amino acids are absorbed by the cells lining the digestive system and then absorbed into the bloodstream