2.1.4

• enzymes

  A biological catalyst that increases the rate of reaction by lowering the reactions activation energy
• intracellular enzymes


  enzymes that work inside a cell
• example of an intracellular enzyme

  catalase

  H2O2 -> H2O + O2
• H2O2 in cells

  comes from metabolic reactions

  Is an oxidising agent that slowly damages cells
• extracellular enzyme


  An enzyme that works outside of cells
• examples of extracellular enzymes

  amylose

  starch -> maltose

  Trypsin

  proteins -> amino acids
• Amylase is produced in

  salivary glands and the pancreas
• amylase is released into

  The mouth and small intestines
• substrate

  the molecule an enzyme attaches to
• product


  the molecule produced from an enzyme reaction
• structure of an enzyme

  globular protein

  Made of hydrophilic and hydrophobic amino acids

  Active site
• Active site

  Where the substrate binds to an enzyme

  Its tertiary structure is complimentary making enzymes specific to molecules
• how are enzymes water soluble?

  Covered in hydrophilic amino acids
• enzyme substrate complex


  A temporary molecule formed when an enzyme and substrate bind
• How to an enzyme and substrate bind

  The amino acids of the enzyme form temporary bonds with the substrate molecule
• enzyme product complex

  A temporary molecule formed after the enzyme reaction but before the product is released
• Lock and key model

  Only 1 specific substrate can fit into a complimentary enzymes active site. the shape of the substrate and active site and the angle that the substrate collides with the active site must be perfect as the active site cannot change shape
• Problems with lock and key model

  Very difficult for a perfect substrate enzyme collision

  Does not explain how some enzymes are more efficient than others
• induced fit model

  When an enzyme approaches its specific substrate the active site changes shape slightly the better fit the substrate and pull it in.
• How does temperature affect enzyme activity?

  Gives molecules more kinetic energy leading to faster movement and more collisions between enzymes and substrate increasing the chance of a successful collision and the overall rate of reaction
• Temperature effect on enzyme rate

  A) inactive

  B) optimum

  C) denatured

  D) vmax

  
• when an enzyme is too cold it

  becomes inactive as there is little kinetic energy so fewer collisions reducing the rate of reaction meaning not all substrate will react
• when an enzyme is too hot it

  dentures as the active site looses its tertiary structure so is unable to react decreasing the rate of reaction so less product is formed
• enzyme temperature rate of reaction is measured using

  Q10 equation
• Q10 equation


  rate of reaction at x + 10 temperature / rate of reaction at x temperature
• what is pH

  the concentration of H+ in a solution
• what bonds to H+ affect?

  ionic

  hydrogen
• Affect of pH on enzyme rate graph

  A) denature

  B) optimum

  C) denature

  
• when enzymes get too cold they do not

  denature
• when enzymes are at a too low ( acidic ) pH what occurs

  there are no H+ for the tertiary structure of the enzyme to interact with so its looses its shape and active site making it unable to react decreasing the rate of reaction
• when enzymes are at an optimum pH what occurs?

  The enzymes tertiary structure interacts with H+ holding its structure
• when enzymes are at a too high pH ( alkali ) what occurs?

  The H+ interact with the polar and charged amino acids and the tertiary bonds destroying the tertiary structure and active site of the enzyme making it no longer able to react decreasing the rate of reaction
• how does enzyme / substrate concentration affect enzymes rate of reaction?

  the rate will increase as there is either more availability for substrates to be broken down or more substrate to be broken down ( if there is no limiting reactant )
• Affect of concentration on enzyme rate

  A) vmax

  
• if there is a limiting concentration of substrate / enzyme what happens to the enzyme rate of reaction?


  If all active sites are occupied or all substrate is already in an enzyme - substrate complex the rate will begin to level out
• inhibitor

  a chemical that binds to an enzyme to reduce its rate of reaction
• allosteric site

  a binding site on an enzyme for chemicals that are not substrate
• competitive inhibitors

  bind to the active site which means substrate is unable to bind and react
• non competitive inhibitors

  bind to the allosteric site changing the shape of the active site meaning it is no longer complimentary to its specific substrate
• reversible inhibitors

  form weak bonds with the enzyme but its effects can be removed by adding more substrate ( if the enzyme is also competitive )