Limiting Factors Affecting Enzymes: pH Flashcards
All enzymes have an optimum pH or a pH at which they operate best
Enzymes are denatured at extremes of pH as
Hydrogen and ionic bonds hold the tertiary structure of the protein (ie. the enzyme) together
Below and above the optimum pH of an enzyme, solutions with an excess of H+ ions (acidic solutions) and OH- ions (alkaline solutions) can cause these bonds to break
This alters the shape of the active site, which means enzyme-substrate complexes form less easily
Eventually, enzyme-substrate complexes can no longer form at all
At this point, complete denaturation of the enzyme has occurred
Where an enzyme functions can be an indicator of its optimal environment example in the stomach
Eg. pepsin is found in the stomach, an acidic environment at pH 2 (due to the presence of hydrochloric acid in the stomach’s gastric juice)
Pepsin’s optimum pH, not surprisingly, is pH 2
When investigating the effect of pH on the rate of an enzyme-catalysed reaction, you can use …………. solutions to measure the rate of reaction at different pH values:
buffer
Buffer solutions each have a specific pH
Buffer solutions maintain this specific pH, even if the reaction taking place would otherwise cause the pH of the reaction mixture to change
What should you control when testing pH
A measured volume of the buffer solution is added to the reaction mixture
This same volume (of each buffer solution being used) should be added for each pH value that is being investigated
Exam Tip
Temperature can both affect the speed at which molecules are moving (and therefore the number of collisions between enzyme and substrate in a given time) and can denature enzymes (at high temperatures). pH, however, does not affect collision rate but only disrupts the ability of the substrate to bind with the enzyme, reducing the number of successful collisions until eventually, the active site changes shape so much that no more successful collisions can occur.
