Molecular biology is a science dealing with molecular basis of genetic or biological specificity. It is biochemistry of genes & specific products & enzymes. The three essential branches of sciences together form molecular biology, are genetics, biochemistry & cell biology.
The double helical structure of DNA proposed by D. Watson & F.H.C.Crick in 1953 led the foundation stone for molecular biology. Even the discoveries like role of DNA in protein synthesis, genetic code & nature of gene regulation, are the pillars of molecular biology.
Except for the viruses, cells are the structural & functional units of all living organisms. Cells contain chromosomes & chromosomes store all the genetic information of the organism in the form of sequence of the nucleotide bases present in DNA. The double stranded complementary structure of DNA allows accurate production of daughter copies of genes, which may be transmitted to progeny.
Molecular biology has application in Recombinant DNA technology, which involves isolation, recombination of DNA fragments to manipulate desired genetic material.
Isolation of DNA can be done with number of methods. One popular way is of eletrophoresis, it picks up desired DNA & discard the undesired part. To cut the specific genes of interest from the rest of DNA, molecular scissors called restriction endonucleases are used. They recognize specific nucleotide sequence in DNA, often 4or 6 base pairs long, & cut both strands of DNA within the recognition site. They are site specific.
In the next step, these DNA fragments are incorporated into the agent called cloning vehicle like bacteriophages & plasmids. DNA ligase is nick sealing enzyme which joins DNA fragment with bacterial DNA to form recombinant DNA molecule. Once foreign gene has spliced in to a cloning vehicle, both vehicle & foreign gene are introduced into a cell that is normally a host for the vehicle. The host of choice in most experiments has been the bacterium Escherichia coli, but other organisms or even cultured cells can be used as hosts.
Normally, the strain of E.coli lacking the restriction system is prepared by incubating exponentially growing cells with Calcium carbonate at low temperature, then DNA is added & mild heat shock result in uptake of DNA.
In final step, the host cell is allowed to multiply, forming a clone having millions of identical cells. By this a piece of genetic information can be transferred into a cell where it would never occur naturally.
Applications of molecular biology
1. production of insulin, humulin by E. coli.
2. production of a large amount of vaccines & antibodies in pure state to act against viral diseases.
3. production of special chemicals like amino acids, vitamins, enzymes which are necessary for normal biological functions.
4. production of class of regulatory proteins of the immune system called interferons which is essential in combating diseases.
5. production of monosex fertility pills to act on pituitary hormones called inhibin.
6. using monoclonal antibodies, scientists are trying to develop specific types of reagents to combat diseases.
7. in discovering more sensitive & quicker methods for detecting & treating hepatitis B,venereal diseases, viral infections, cancer, AIDS etc. u
- The author is pursuing her B.Pharm (TY) at D.Y.Patil College of Pharmacy, Pimpri, Pune