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MCAT BioChem Question — Enzyme Catalyst

  • by Allison Chae
  • Dec 03, 2014
  • MCAT Biology, MCAT Blog, MCAT Chemistry, MCAT Question of the Day
  • Reviewed By: Liz Flagge

An enzyme catalyst is kept in a solution buffered to the pH that maximizes activity for those enzymes found in the blood. The enzyme catalyzes a reaction that produces an acid whose pKa is 4.5. In this buffer solution, the acid product will be:


A) Primarily deprotonated

B) Primarily protonated

C) Protonated and deprotonated in roughly equal amounts

D) Not formed




The blood has a pH around 7.4, making it somewhat basic. If this enzyme is in a solution buffered to a point to maximize enzymes found in the blood, then the buffer solution will have a pH of 7.35 to 7.45.


When an acid is in a solution whose pH is higher than its pKa, the acid is deprotonated, making choice (A) the correct answer.


B: The acid would be protonated if the buffer solution had a pH that was below 4.5

C: The acid would have equal concentrations of the acid and conjugate base form if the buffer had a pH of around 4.5

D: There’s no reason for us to assume the product wouldn’t form.


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