DNA as the Genetic Material

Everyone received a surprise in the scientific research community after getting the idea that discovery of genetic material(dna) was done while conducting clinical research on the Streptococcus pneumoniae Bacterium. No one ever imagined that the experiments conducted on a bacterium could lead to such a huge discovery of the lifetime. The bacterial isolate and samples of the serum from the studies of the research provided the reagents which were clinical for the ultimate experiment which proved DNA as the hereditary material

BACTERIAL RESEARCH : CRITICAL INFORMATION ON DNA?

Many scientists were engaged with several experiments on bacteria during the twentieth century.  Two of those scientists played a major role in the discovery of DNA as the ultimate genetic material. Oswald Avery was one of them. He joined the Rockfeller institute of medical research.which is famous for treatment of lobar pneumonia. He believed that knowledge over the bacterium could prove helpful in curing a lot of diseases in the upcoming future. He always focused on the chemical composition because it was important for treating the disease. He concentrated on the chemical composition of the capsule that was surrounding the virulent S strains of the bacteria. He discovered that polysaccharides were the major component in those capsules and those capsules had very different polysaccharide compositions. 

At a certain time in England,a scientist named Frederick Griffith was investigating different serotypes of the streptococcus bacterium which appeared in patients. He discovered two different forms of bacteria one was R(rough) and other was S (smooth) which were basically divided in terms of observing their surface. He conducted an experiment on mice. He observed that mice unexpectedly died when he injected them with type1 R and heat killed type 2 S pneumoniae cocci. He then again observed mice injected with heat killed type 1 S and living type 2 R, DIED. He concluded from the above experiments that a substance capable of withstanding a heat treatment could have been transferred from a non living S cells to living R cells converting them into virulent. By which R cells transformed into S cells of donor serotype.

Hershey and Chase experiment: the unequivocal proof of DNA as a genetic material:

Two scientists ALfred Hershey and Martha Chase performed a series of experiments at Carnegie Institute in washington. He came to the conclusion that genes were composed of DNA(deoxyribonucleic acid). These experiments were later named the Hershey and Chase experiment. These experiments were performed on Bacteriophages(viruses that infect bacteria). Scientists were all kept in scepticism for a long time that whether genetic material was truly protein or DNA?. Waring blender experiments, which was one of the most popular experiments among the hershey chase experiments,provided arguably one of the most concrete pieces of evidence about DNA as genetic material. These led to an idea that genes were made up of DNA. These discoveries allowed many research workers to investigate the molecular mechanism of organisms which involves a gene function.

In 1935, three scientists named Oswald Avery, Colin Macleod, and Maclyn McCarty, performed an experiment that proved that DNA facilitated Bacterial Transformation. Bacterial Transformation is the process by which a bacterium can get a new genetic material from the surrounding. A non disease bacterium can be transformed into disease bacterium. The scientists found that the inherited factor due to which bacterial transformation occurs contained DNA.

Conclusion

In the twentieth century, many research scientists argued whether the gene was protein or DNA. how an organism grows, colour, morphology everything is controlled by genes. Every chemical composition of DNA was identified by 1900. They concluded that every cell contains DNA, although DNA’s function was unidentified. Some scientists at that time believed that protein consisted of much more building blocks so genes must have been composed of protein and not DNA. Hershey and Chase were keen to determine if the replicating piece of the bacteriophages were solely DNA.