AP Syllabus focus:
‘Enzymes are protein catalysts that lower activation energy, increasing the rate of biological reactions in cells.’
Enzymes make cellular chemistry fast enough to sustain life. They do this by catalysing reactions: accelerating reaction rates under mild cellular conditions while remaining unchanged, enabling metabolism to proceed efficiently and selectively.
What enzymes are
An enzyme is a biological catalyst. Most enzymes are globular proteins whose three-dimensional shapes create chemical environments that promote specific reactions.
Enzyme: A protein catalyst that increases the rate of a chemical reaction by lowering activation energy, without being consumed by the reaction.
Practice Questions
FAQ
No. Some need cofactors (e.g., metal ions) or coenzymes (organic molecules) to complete catalysis, while others are fully functional as protein alone.
Amino-acid substitutions can subtly alter folding or local chemistry, reducing transition-state stabilisation or reactant positioning, which raises effective activation energy and slows the reaction.
Specificity refers to the reaction chemistry promoted. The same catalytic features that lower activation energy for the forward reaction also lower it for the reverse under appropriate concentrations.
Yes. Some RNA molecules act as catalysts (ribozymes), using folded structures to stabilise transition states, though many cellular catalysts are proteins.
They track reaction rate by monitoring product formation or substrate disappearance over time (often via colour change, fluorescence, or absorbance), then compare rates with and without enzyme present.
