Properties of Genetic Material (DNA versus RNA)
DNA acts as genetic material. However, it subsequently became clear that in some viruses, RNA is the genetic material (For example, Tobacco mosaic viruses, QB bacteriophage, etc.)
A molecule that can act as a genetic material must fulfil the following criteria :
(i) It should be able to generate its replica (Replicaton)
(ii) It should chemically and structurally be stable.
(iii) It should provide the scope for slow changes (mutation) that are required for evolution.
(iv) It should be able to express itself in the form of ‘Mendelian Characters’.
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 fulfil criteria itself.
The genetic material should be stable enough not to change with different stages of life cycle, age or with change in physiology of the organism. 2’-OH group present at every nucleotide in RNA is a reactive group and makes RNA labile an 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. In fact, the presence of Thymine at the place of Uracil also confers additional stability to DNA.
Both DNA and RNA are able to mutate. In fact, RNA being unstable , mutate at a faster rate. Consequently, viruses having RNA genome and having shorter life span mutate and evolve faster. RNA can directly code for the synthesis of proteins, hence can easily express the characters. DNA, however, is dependent on RNA for synthesis of proteins. The protein synthesizing machinery has evolved around RNA.
The above discussion indicate that both RNA and DNA can function as genetic material, but DNA being more stable is preferred for storage of genetic information. For the transmission of genetic information, RNA is better.