Why is DNA Considerd a better hereditary material than RNA?
class 12th CBSE Biology sample paper
Answers
A molecule that can act as a genetic/hereditary material must fulfill the following criteria:
(i) It should be able to generate its replica (Replication).
(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’.
.
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.
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, 2'-OH group present at every nucleotide in RNA is a reactive group 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.
.
In fact, the presence of thymine at the place of uracil also confers additional stability to DNA. (Detailed discussion about this requires understanding of the process of repair in DNA, and you will study these processes in higher classes.) 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.
1. The 2-OH group present at every nucleotide in RNA is reactive and makes RNA labile and degradable. But, DNA is less reactive and structurally more stable.
2. The presence of Thymine in place of Uracil in DNA confers it additional stability. One major problem with using uracil as a base is that cytosine undergoes deamination and gets converted into uracil. This is not a rare reaction; it happens around 100 times per cell, per day. This is no major problem when using thymine (as in the case of DNA), as the cell can easily recognize that the uracil doesn't belong there and can repair it by substituting it by a cytosine again.