191.

Define enzymes. How do enzymes differ from ordinary chemical catalysts? Comment on the specificity of enzyme action. What is the most important reason for their specificity? Explain the mechanism of enzyme catalysis.

Enzymes are biocatalyst produced by the living cells which catalyse many biochemical reactions in animals and plant bodies. Enzymes are protein substances.

Enzymes differ from ordinary chemical catalysts in the following ways:
(i)    Enzyme catalyst the reaction by about million times faster than the normal chemical catalysts.
(ii)    Enzymes are very specific in their action. Each biochemical reaction requires a particular enzyme for it.
(iii)    Enzymes work under milk conditions of temperature and at specific pH.

Specificity of enzyme action : Enzymes are extremely specific; Each reaction is generally catalyzed by a particular enzyme. For example, hydrolysis of urea is catalysed by only urease and none of the several thousand other enzymes present in the cell catalyse this reaction.



The specificity of enzymes results from the fact that each enzyme has a specific active site one its surface. When the reactant molecules, called the substrates of the reaction bind at the active site, a chemical change is initiated. In most of the cases, substrates bind to the active site through inter-molecular forces like H-bonds, dipole forces and other weak attraction.

Mechanism of enzymatic reaction involves four stages:
(i) The formation of complex between enzyme and substrate.



(ii) The conversion of this complex to an enzyme-intermediate complex



(iii) Further conversion of El to a complex between enzyme and product (EP)



(iv) The dissociation of the enzyme-product, leaving the enzyme unchanged