H1 Biology and H2 Biology

What are the effects of pH on the rate of enzyme-catalysed reactions?

Notes from the video ‘H2 Biology Tuition | H1 Biology Tuition | Effect of pH on Rate of Enzyme-Catalysed Reaction’:


In this Biology tutorial, we would learn about the effects of pH on the rate of enzyme-catalysed enzymes.


Each enzyme has an optimum pH.
At this pH, the intramolecular bonds and ionic bonds which maintain the shape and charge of the secondary and tertiary structures of the enzyme are intact and the active site is most ideal for substrate binding. This results in the highest rate of formation of enzyme-substrate complex formed and the maximum rate of reaction.


Any deviation from the optimum pH results in excess H+ or OH ions which affects the ionization of charged R-groups of charged amino acids. Excess H+ results in the COO groups gaining a hydrogen to become COOH while the excess OH minus results in NH3+ becoming NH2. This affects the structural residues and the catalytic residues and contact residues in the enzyme.

Structural Residues of Enzymes

When R groups of structural residues are altered, the ionic bonds and hydrogen bonds that stabilize the specific 3D conformation of the active site are disrupted, resulting in denaturation of the enzyme and the loss of specific shape of the active site.


Catalytic Residues and Contact Residues

The interaction between the substrate and the enzyme active site is also affected. The specific charges of the R groups of catalytic residues and contact residues in the enzyme active site may also be changed due to the excess H+ or OH- ions  . This results in the loss of catalytic activity and the disruption of the ionic and hydrogen bonds between the active site of enzyme and substrate respectively.


The enzyme’s active site is no longer complementary in shape and charge to the substrate and rate of formation enzyme-substrate complexes is reduced. This leads to a lower rate of reaction.

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