Rate Concentration Graph for Enzyme Catalysed Reaction

Let's take a look at the rate concentration graph of a reaction catalysed by enzymes.

enzyme catalysed reaction rate conc graph

Notice the rate increases initially then becomes constant as reactant concentration increases.

We can treat this as a combination of 2 separate graphs.

enzyme catalysed reaction combi of 2 graphs

The point of intersection of these 2 graphs will coincide at the concentration of enzyme.

1. Reactant concentration less than enzyme concentration

enzyme catalysed reaction rxt less than enzyme graph

When reactant concentration increases, there are enough enzymes to catalyse the additional reactants.

This leads to a proportionate increase in the rate of reaction.

enzyme catalysed reaction rxt less diagram

The reaction is first order with respect to reactant and rate equation is as follows:

rate = k [reactant]

2. Reactant concentration more than enzyme concentration

enzyme catalysed reaction rxt more than enzyme graph

At this stage saturation is reached and all the enzymes are fully utilised.

When reactant concentration increases, there is no additional enzymes to handle the catalysis.

Hence rate reaches a maximum and does not increase any further.

enzyme catalysed reaction rxt more diagram

The reaction is zero order with respect to reactant and rate equation is:

rate = k

Therefore the rate concentration graph of an enzyme catalysed reaction is summarised here:

enzyme catalysed reaction summary

[reactant] less than [enzyme], first order wrt reactant, rate = k[reactant]
[reactant] more than [enzyme], zero order wrt reactant, rate = k

Topic: Kinetics, Physical Chemistry, A Level Chemistry, Singapore

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