H1 Biology and H2 Biology

Describe the Mode of Action of Enzymes

Notes from the video ‘H2 Biology Tuition: Mode of Action of Enzymes’:


In this Biology tutorial, we would learn about the mode of action of enzymes.

Enzymes have a specific active site which is complementary in conformation and charge to the substrate. Effective collisions between enzyme and substrate form a temporary enzyme-substrate complex.


Enzyme-substrate complexes

Enzyme-substrate complexes are held together by weak interactions such as hydrogen bonds, ionic bonds, and hydrophobic interactions.
Based on the lock-and-key hypothesis, enzyme is the lock and substrate is the key.
Based on the induced fit hypothesis, the substrate induces a change in shape in the enzyme’s active site such that the active site is a more precise fit for the substrate for effective catalysis.


Enzymes lower the activation energy barrier by:
A. Aligning substrates next to each other in the active site to increase the chances of the reaction occurring.
B. Causing strains on the bonds in the substrate to be broken as they bind to the active site.
C. Orientating the substrates such that their bonds are exposed to chemical attack
D. Providing a favorable microenvironment
E. Participating directly in catalysis with R groups of amino acid residues in acid-­‐base catalysis.
This increases the proportion of substrate molecules with energy greater than the activation energy which allows the reaction to proceed faster than an uncatalysed reaction.


The products of the reaction no longer fit the active site and are released; the enzyme remains unchanged and can be used again.

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