properties of genetic material

Building block of genome : 

Considering the above properties of genetic material, two macromolecules, DNA and protein were strong contenders for qualifying as genetic material, and long debate existed in the first half of twentieth century supporting each of these two polymeric molecules. Both were long molecules, composed of multiple of

monomeric units, abundant in cell fulfilling the primary criteria of genetic material. The fact that genetic information contained in the genome is coded in a long polynucleotide chain known as deoxyribonucleic acid or DNA was elucidated by a number of observations. In 1928, F. Griffith discovered that a transforming

principle present in dead IJipiococcus pneu maniac ceLls can convert nonvirulent strains into virulent ones and live virulent strains with altered genotype can be recovered from infected mouse. Following the lead Avery, MacLeod and McCarty established in 1944 that the transforming principle that converts nonvirulent strains to virulent types is DNA. In a series of experiments they showed that if the mixture of heat killed cells of virulent strain and live nonvirulent strain are treated with enzyme that degrade DNA, transformation

is not observed. However, when treated with protein degrading enzymes, transformation was not hampered suggesting DNA, not protein is the genetic material. Finally in 1952 Alfred Harshey and Martha chase labeled proteins with radioactive S and DNA with P in bacteriophage T2, infected E. coil with the labeled phages and observed that when DNA was labeled, radioactivity was observed inside the host cell while proteins were labeled,radioactivity was found outside host. The fact that proteins contain sulfur but no phosphorus, and DNA contains phosphorus but no sulfur along with the observations proved beyond doubt that the viral genome that infects E. coil consists of DNA.