Which of the following is/are the conditions that a molecule must fulfil to act as genetic material? 1. Replication 2. It should be stable chemically and structurally. 3. Scope for Mutation
A molecule that can act as a genetic material must fulfil the following criteria: It should be able to generate its replica ( Replication ). Hence statement 1 is correct. It should be stable chemically and structurally. Hence statement 2 is correct. It should provide the scope for slow changes ( mutation ) that are required for evolution. Hence statement 3 is correct. It should be able to express itself in the form of 'Mendelian Characters’. If one examines each requirement one by one , because of the rule of base pairing and complementarity, both the nucleic acids ( DNA and RNA ) have the ability to direct their duplications. The other molecules in the living system , such as proteins fail to fulfill the first criteria. Thegenetic material should be stable enough not to change with different stages of the life cycle, age, or with a change in the physiology of the organism. Stability as one of the properties of genetic material was very evident in Griffith’s ‘transforming principle ’ itself that heat, which killed the bacteria, at least did not destroy some of the properties of genetic material. This now can easily be explained in light of the DNA that the two strands being complementary if separated by heating come together, when appropriate conditions are provided. Further, the 2'-OH group present at every nucleotide in RNA is reactive and makes RNA labile and easily degradable. RNA is also now known to be catalytic, hence reactive. Therefore, DNA chemically is less reactive and structurally more stable when compared to RNA. Therefore, among the two nucleic acids, the DNA is a better genetic material.