Effect of temperature on enzyme action

• what is the energy of movement?

  kinetic energy
• what happens to the number of collisions between molecules or ions in solution if temperature increases?

  Increases due to increase in kinetic energy (more collisions) so the molecules move around more, bumping/colliding more
• why is the reaction rate faster at a higher temperature?

  • higher rate of collisions between molecules/ions and beaker
  • more particles have more kinetic energy, are automatically exceeding activation energy
• describe what happens to the tertiary structure of an enzyme if you increase the temperature?

  • tertiary structure is stabilised by many weak bonds (hydrogen bonds and ionic bonds) and if enough of these bonds are broken the tertiary structure 'unravels'.
  • active site shape is lost and the enzyme is denatured - this does not change the primary structure as peptide bonds are not broken
  • covalent bonds aren't broken either
• what is the definition of denaturation?

  an irreversible change in tertiary structure of a protein molecule, leading to the loss of the function of most proteins/enzymes
• how does a large increase in temperature lead to the permanent loss of function of an enzyme?

  • at higher temperatures, the molecules in weaker hydrogen bonds holding and stabilising the tertiary structure vibrate as their kinetic energy increases
  • hydrogen bonds are broken and tertiary structure is no longer stabilised
  • active site is no longer complementary (enzyme is denatured) - substrate can't bind to active site so no enzyme-substrate complexes form
  • activation energy is not lowered and reaction can't occur
• why is denaturing permanent, even if the temperature decreases?

  • broken hydrogen bonds can't reform in same place, and some new bonds would form elsewhere - new covalent bonds may form between newly positioned R-groups that reinforce the 'wrong' not-complementary shape
• what is the optimum temperature of most enzymes?

  40-50 degrees Celsius - work well at 37 but work better slightly higher as there is an increase in temperature when fighting bacteria as they are more susceptible to temp (function in immune system)
• why is the normal body temperature in mammals slightly below optimum temperature of most enzymes?

  this gives a 'safety zone' to prevent enzymes being denatured in the event of an increase in body temperature (e.g. exercise)
• what type of enzymes work well at high temperatures?

  • enzymes from bacteria living near a hydrothermal vent
  • Taq polymerase used in polymerase chain reaction
• what type of enzymes work well at low temperatures?

  • enzymes from red algae that grows on ice - more flexible active site so less stable than enzymes that work at higher temperature
• which type of bond will stabilise the structure of heat resistant enzymes?

  Disulphide bonds as they are strong, stable covalent bonds that are not easily broken by high temps
• what does an increase in kinetic energy do to the activation energy?

  • molecules collide with more force as they are moving at greater speed - so more molecules possess the activation energy
• how does a temperature graph show how temperature affects the rate of reaction?

  • initial incline shows increase in rate of reaction due to an increase in temperature up to around 43 degrees (optimum temperature)
  • this top point on the graph is the Vmax
  • then the line declines showing a decrease in rate of reaction as the temperature decreases as the temperature increases above the optimum temperature - weaker stabilising bonds in enzymes have broken which held tertiary structure in place
• what is the Vmax?

  the maximum rate of reaction
• what is the Q10 (temperature coefficient)?

  a measure of how much the rate of reaction increases with a 10 degree rise in temperature, for most enzymes this is 2 (i.e. the rate doubles for every 10 degree rise in temperature)

  • a value of 1 or more means that the rate is increasing
  • a value of less than 1 means that the rate is decreasing
• how do you calculate the Q10?

  rate at the high temp / rate at low temp (10 degree difference)
• describe the trend of Q10 in a graph?

  Q10 increases to optimum rate (30-40 degrees), but then begins to decrease due to denaturing of enzymes meaning less enzymes available (less active sites) to catalyse a reaction, slowing it down
• why is there a change in Vmax depending on the temperature?

  • at colder temperatures, less kinetic energy is available so molecules vibrate less, meaning a lower Vmax
  • at hotter temperatures, more kinetic energy is available so molecules vibrate more, meaning a higher Vmax