How do enzymes catalyze a chemical reaction in the living system? Explain drug target interaction taking the example of enzyme as target.
1st part: catalytic action of enzymes-
• Enzymes are said to be biochemical catalysts, chemically which are just proteins.
• They only catalyze (enhances rate or betterment of a biochemical reaction) the biochemical reactions in the living systems without changing chemically.
• They are highly specific( binds to a certain substrate only); this specificity comes from possession of an active site.
• The shape of the active sites of any enzyme is cavity like in structure, which is built in such a way that only a specific substrate can fit there. (resembles the system of key-lock fitting).
• In their catalytic activity, the enzymes perform 2 major functions:
(i)
o At first, the enzyme would orient itself to hold a specific substrate for a chemical reaction.
o The active site of enzymes holds that substrate molecule in such a suitable position, that the reagent( chemical substance with which the substrate reacts) can attack the substrate effectively
o Substrate binds to the active site of the enzyme through a variety of interactions like-
Ionic bonding, hydrogen bonding, van der Waals interaction or even through dipole-dipole interaction results in formation of enzyme-substrate complex, which later leads to the desirable product molecule(produced by substrate-reagent interaction).
(ii)
o The second function of the enzymes will be providing functional groups(reagents) that will attack the substrate and the chemical reaction will be carried out in the living body.
o Eg- 
o
Urea, the substrate water, the reagent,
Urease is the enzyme which catalyses the reaction and results in formation of the product i.e. ammonia.
2nd part:
Drug –target interaction (enzyme being the target)-
• Enzyme s are a major target for inhibitors like drugs.
• Drugs inhibit the natural activities of enzymes.
• They can block the active site of enzymes which leads to prevention in binding of the substrate to that binding site, thus drugs inhibit the catalytic activity of the enzyme, that is why they are called the enzyme inhibitors.
• There are 2 such ways by which drug-enzyme interaction occurs:
•
The competitive and non-competitive inhibitions.
o When drugs are competing with natural substrate (by mimicking their chemical structures) for attachment to the active site of enzymes, such drugs are called competitive inhibitors.
In another way, there are some other drugs too that do not directly bind to the active sites of the enzymes. Instead, they bind to a different site than the active site, which is called allosteric site.
This bondage changes the shape of the active site resulting the substrate not able to identify it, therefore no enzyme-substrate interaction occurs.
• Generally, if the bond which is formed between enzyme and the inhibitor is strongly covalent in nature that cannot be dissociated easily and enzyme gets blocked permanently.
• Then the body have to degrade enzyme-inhibitor complex & synthesize new enzyme.