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A-Level Biology OCR A

Ph Change H Optimum Bonds R Groups Active Site

Front Explain why a pH change away from optimum decreases the rate of reaction.
Back pH change from optimum:
  • Hydrogen bonds and ionic bonds between amino R-groups hold protein in its precise 3D shape
  • Change in pH changes H+ concetration (more H+ - acidic - low pH) (less H+ - alkaline - high pH)
  • Active site is only in right shape at optimum pH so when it changes, structure and therefore active site is altered
  • This reduces the rate
  • If change is not too significant, enzyme can renature if pH is back to optimum
  • If change is too significant the enzyme is irreversibly altered, active site no longer complementary - denatured
  • Happens because H+ intreact with polar and charged R-groups if more H+ less R-groups can interact with each other leading to ionic and hydrogen bonds breaking

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