Simulation · Biology · Class 11

What does an enzyme change?

From the lesson How enzymes speed up reactions in Biomolecules. Change the values and watch what happens.

The idea behind it

NCERT §9.8.2, §9.8.3

The chemical an enzyme converts is its substrate (S), and the result is the product (P): S → P.
The substrate must diffuse to the active site and bind there, so the formation of an enzyme-substrate complex (ES) is obligatory. It lasts only a short time.
While bound, the substrate takes on a new, unstable transition state structure. Once the bonds are broken or made, the product is released from the active site.
On a graph of potential energy against the progress of the reaction, the substrate must climb to the higher energy of the transition state before falling to the product. If P lies lower than S the reaction is exothermic and needs no heating.
Whether the reaction releases energy or needs it, the energy gap between S and the transition state is the activation energy. Enzymes lower this barrier, which makes the change from S to P easier.
The overall scheme is E + S ⇌ ES → EP → E + P, where EP is the enzyme-product complex. Formation of ES is essential for catalysis.
The catalytic cycle: the substrate binds to the active site; binding makes the enzyme change shape and fit more tightly around it (induced fit); the active site breaks the substrate's bonds and an enzyme-product complex forms; the enzyme releases the products and is free to bind another substrate molecule.

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