BOTANY Higher Secondary Second Year - Textbooks Online

Mechanism of enzyme action
In a biochemical reaction, there is an energy barrier between the
reactants and the products. Only those molecules which possess a certain
amount of excess energy above the average energy of normal molecules
are able to react to form products. This excess energy which a normal
molecule must aquire in order to react is known as energy of activation
(Ea). This energy of activation determines the rate of reaction. Higher the
value of Ea, lower is the rate of reaction and greater stability. At higher
ProductsPotential energy
Reactants
Energy of
activation
without
enzyme
Energy of activation
with enzyme
Products
Reaction co-ordinates
Fig. 5.4 Mechanism of enzyme action
temperature, the rate
of chemical reaction
becomes faster, because
increased temperature brings
about increased number of
activated molecules. But in
the case of enzyme catalyzed
reaction, the rate of reaction
is optimum at normal body
temperature. Because all the
molecules either energy-rich
or energy-poor combine with
the active site of the enzyme
to form enzyme substrate complex. The latter breaks into enzyme and
product. Thus, the enzyme acts by lowering the energy of activation of
the reactions i.e. reducing the energy barrier and increases the rate of
reaction.
Self evalution
I . Choose and write the correct options.
1. The term enzyme was coined by
a. Kuhne b. Fischer
c. Buchner d. Koshland
2. The lock and key theory of enzyme action was proposed by
a. Kuhne b. Fischer
c. Buchner d. Koshland
3. An example for transferase is
a. transaminase b. pyruvic carboxylase
c. histidine decarboxylase d. G-3-P dehydrogenase
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