Mechanism of enzyme action
The cellular environment normally does not favour a chemical reaction as the biological molecules are quite stable in aqueous environment in the cell at fixed temp and pH. The activation of substrate is prerequisite to overcome the transition state and to proceed the reaction in desire direction.the activation of the substrate is done by the enzyme. How the enzyme decreases the activation energy ,It will be discussed below.
Active sites
The enzymes have a ability to bring the substrate closer and in suitable orientation so as to favour the formation of ES ( enzyme substrate complex ) , the substrate binds to the enzyme at specific place or site called active sites.it is so designed that it will occupy by only the selected molecules, these sites have specific amino acid residues which establish covalent links with the substrate, this links provides the formation of transition state and hence lower the activation energy.each enzyme have different shapes of active sites which depends on the number and type of amino acid involved in binding with substrate and nature of the cofactors. Active site is a 3 D cleft and is a small part of the enzyme.
Binding of enzyme and substrate by multiple interactions
The amino acids of the enzyme binds to the substrate by a number of noncovalent interactions such as vanderwal force , hydrogen bonds, and hydrophobic interactions . since the hydrogen bonds are formed in the definite direction ( possible when the substrate have bind forming part in the appropriate position and direction) ,it also a factor of specificity of the enzyme.
Specificity of the enzyme
The bonding of a enzyme and the substrate is very specific , the active site have unique geometry and is complementary to the geometry of the substrate molecule, some enzymes have absolute specificity for only one enzyme while others react with more than one substrates with the same functional groups. The enzyme catalysed a chemical reaction at a particular chemical bond regardless of others structural features.two theories are available to explain this specificity.
i. Lock and key theory
ii. Induced fit theory.
How enzyme lower the activation energy
We know that the enzyme enhance the rate of reaction by lowering the activation energy.dor this purpose some amount of energy must be needed ,where dose the energy come from ?
The amino acids residues of enzyme at active sites interact with the substrate molecules by some weak and strong interactions , weak interactions initiate the bonding between the substrate and the active site .in the process the substrate reaches a transition state ., which is the highest energy state . the formation of each such weak interactions releses some free energy which enhances the total energy of the enzyme- substrate complex and stabilised it . the free energy release is called binding energy which helps the enzyme- substrate complex to overcome the barrier and to proceed the reaction in foreward direction. Thus the binding energy is the source of energy used by enzyme to lower the activation energy.
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