enzymes

• ENZYMES:

  • globular proteins
  • biological catalysts
  • catalyse metabolic reaction
  • can affect structures (collagen) in organisms, and function (respiration)
  • enzyme action can be extracellular or intracellular
  • have active site: specific shape where substrate molecule bind to
  • highly specific due to tertiary structure
• enzymes function:

  • lower activation energy of reaction
  • speed up reaction
  • when substrate fit into enzyme active site forms enzyme-substrate complex, which lowers activation energy by:
  • 2 substrate molecule joined enzyme hold close together, reduce repulsion between molecules and bond more easily
  • enzyme catalyse breakdown reaction, fit into active site, put strain on bond on substrate, substrate molecule easily breaks up more easily
• INDUCED-FIT MODEL:

  • substrate may not fit fully onto enzyme active site
  • so upon joining active site changes shape of active site slightly to fit the shape of substrate more closer so reaction can occur
  • once catalysed products leave active site and enzyme changes back into original shape
• Factors affecting enzyme action:

  • Temperature: rate of enzyme activity increases as temperature increases, more kinetic energy, molecules move faster, higher frequency of successful collisions. If temperature is above the optimum, the tertiary structure is altered, so the active site is altered, and the reaction stops as the substrate is no longer complementary.
  • pH: enzymes have an optimum pH at which they work best; alteration means denaturation of the enzyme and substrate, making the active site no longer complementary.
  • Concentration of enzyme: more enzyme molecules increase the likelihood of substrate collisions and the formation of enzyme-substrate complexes. If the substrate is limited, there is no more reaction since the enzyme no longer has substrate available.
  • Concentration of substrate: more substrate leads to more successful collisions, up to the saturation point where all active sites are taken up
• Enzyme activity can be inhibited:

  • Competitive inhibition: molecules with a similar shape to the substrate compete to bind to the active site, blocking it and preventing the substrate from binding and reacting.
  • Non-competitive inhibition: molecules bind to the enzyme but not at the active site, causing changes in shape so the substrate molecule can't bind. This inhibition is non-competitive because the inhibitor has a different shape to the active site and binds to a different part of the enzyme
• measuring enzyme-catalysed reaction:

  • formation of products of reaction, e.g. vol of oxygen produced when enzyme catalyse acts on hydrogen peroxide (time vs vol produced)
  • disappearance of substrate, e.g. reduction in conc of starch when acted by amylase (time vs mass)
  • measure rate of change at point: gradient of tangent at a point