The chemical or metabolic conversion refers to a reaction. The chemical which is converted into a product is called a .substrate. where as enzymes is proteins with three dimensional structures including an .active site., convert substrate (S) into a product (P) symbolically / written :
`S to P`
substracte rarr product
The substrate binds with the enzyme at its .active site.. The substrate has to diffuse towards the active site. Thus ES complex (Enzyme substrate complex) is formed.
This complex formation is a transient phenomenon. During the state where substrate is bound to the enzyme active site, a new structure is formed transition state structure.
After the bond breaking is completed the product is released from the active site.
The path way of this transformation go through the transition state structure. There could be many more altered structural states between the stable substrate and the product. All these intermediate structure states are unstable.
If this depict as pictorially through graph Y-axis represents the potential energy content, X-axis represents progression of .transition state..
There is difference between the energy level of substrate (S) and product. If .P. is at a lower level than .S., the reaction is an exothermic reaction. One need not supply energy (by heating) in order to form product.
However, whether it is an exothermic or spontaneous reaction or an endothermic or energy requiring reaction, the .S. has to go through a much higher energy state.
The difference in average energy content of .S. from that of this transition state is called .activation energy..
Enzymes eventually bring down this energy barrier making the transition of .S. to .P. more easy.
