Illustrate lock and key hypothesis of enzyme action



Mechanism of Enzyme Action:
(1) The working of enzymes is a complex one.
(2) All enzymes first of all combine with the respective substrates before yielding the products of the reactions they catalyze.
(3) In other words, enzymes with substrates form an intermediate complex before decomposition of the substrate can occur.
(4) This two way reaction can be represented as follows:

1st step : Enzyme + Substrate = Enzyme Substrate Complex.
2nd step: Enzyme Substrate Complex = Enzyme +
Product ยง
(5) The enzymes must combine first with substrate molecule in order to act.
(6) In order to explain the mode of action of enzyme, Fischer proposed a Lock and Key theory. According to him, if the right key fits in the right lock, the lock can be opened, otherwise not.

(7) It is believed that molecules have specific geometric shapes. Proteins are able to act as enzyme primarily because their shape provides surface configurations into which other molecules can fit.
(8) The molecules which are acted upon by the enzymes are called substrates of the enzymes

(9) Under the above assumption only those substrate molecule with the proper geometric shape can fit into the active site of the enzymes.
(10) However under special circumstances some other molecules which are similar to the substrate can also combine with the active site of an enzyme.
(11) If this happens, the above molecules may complete
with the substrate and the reaction may either slow down or stop.
(12) Such susbtances are called as the competitive
inhibitors as they act to prevent the production of a substance