1.8 - Factors Affecting Enzyme Action

• how temperature affects enzyme activity

  as temperature starts increasing molecules' kinetic energy increases so they move faster so more successful collisions between enzyme and substrate so more ESC form so faster rate of reaction

  as temperature keeps rising hydrogen and other bonds in the enzyme break so active site changes shape slightly substrate fits less well and enzyme activity slows down

  as temperature keeps rising the enzyme is so disrupted that it stops working and is denatured
• denaturation

  a permanent change to the active site causing enzyme to stop working
• optimum temperature for enzymes in the human body

  40°C
• why is there a gap between our human body temperature and the optimum temperature for enzymes in the body

  more energy would be needed to maintain a higher body temperature

  other proteins may denatured at higher temperatures

  at higher temperatures any rise in temperature would denature enzymes
• how pH affects enzyme activity

  a change in pH alters charges on amino acids that make the active site so substrate won't fit as well so enzyme activity decreases

  a significant change IN pH can break ionic and hydrogen bonds that hold the tertiary structure of the enzyme so active site changes shape so enzyme is denatured
• what determines the arrangement of the active site

  hydrogen and ionic bonds between -NH2 and -COOH groups of the polypeptide
• optimum pH for most human enzymes

  pH 7
• how enzyme concentration affects enzyme activity

  as long as there's an excess of substrate, increasing enzyme concentration increases rate of reaction proportionally because the excess substrate will be acted on by the enzyme
• lower enzyme concentration

  not enough enzymes to allow all substrates to find an active site at the same time so rate of reaction is half the maximum possible for the number of substrates available
• intermediate enzyme concentration

  all substrates an occupy an active site at the same time so rate of reaction doubles as all active sites are filled
• high enzyme concentration

  there are already enough active sites for all substrates so adding more enzymes won't increases the rate of reaction
• how substrate concentration affects enzyme activity

  the higher the substrate concentration the faster the rate of reaction due to more collisions between enzyme and substrate

  this is only up to a certain point: after all active sites are full more substrates won't make a difference

  substrate concentration lowers over time so rate of reaction will decrease so initial rate of reaction is the highest
• low substrate concentration

  not enough substrates to fill all active sites so enzymes have a limited number of substrates to collide with so active sites aren't working at full capacity so rate of reaction is half the maximum possible for the number of enzymes available
• intermediate substrate concentration

  all active sites are filled so rate of reaction is at a maximum - saturation point
• high substrate concentration

  no increase in rate of reaction as all active sites are already filled so substrate is in excess