Which statement about enzymes is correct?
- A. They are consumed in the reactions they catalyse
- B. They remain chemically unchanged at the end of the reaction
- C. They can catalyse reactions that would otherwise be thermodynamically impossible
- D. They work equally well at every pH
Explanation
An enzyme releases the product and returns to its original state, ready to bind the next substrate molecule, which is why a small amount catalyses the conversion of a great deal of substrate. Enzymes only speed up reactions that were already energetically favourable; they cannot drive an unfavourable one. Each has a narrow pH optimum outside which activity falls off.
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