5.2 In search of the genetic material · Part 2

RNase (an enzyme which destroys RNA) and proteases (an enzyme which destroys protein) did not affect the transformation. Digestion with DNase inhibited transformation suggesting that the DNA caused the transformation. These experiments suggested that DNA and not proteins is the genetic material. The phenomenon, by which DNA isolated from one type of cell (S – strain), when introduced into another type (R-strain), is able to retain some of the properties of the S - strain is referred to as transformation . Fig. . Transformation experiment of Avery et. al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td Biology-Zoology Chapter- XII Std Biology-Zoology Chapter- Molecular Genetics phages (virus) are added to bacteria, they adsorb to the outer surface, some material enters the bacterium, and then later each bacterium lyses to release a large number of progeny phage. Hershey and Chase wanted to observe whether it was DNA or protein that entered the bacteria. All nucleic acids contain phosphorus, and proteins contain sulphur (in the amino acid cysteine and methionine). Hershey and Chase designed an experiment using radioactive isotopes of Sulphur ( S) and phosphorus ( P) to keep separate track of the viral protein and nucleic acids during the infection process. The phages were allowed to infect bacteria in culture medium which containing the radioactive isotopes S or P. The bacteriophage that grew in the presence of S had labelled proteins and bacteriophages grown in the presence of P had labelled DNA.