TRANSFORMING PRINCIPLE
Read the following passage carefully and answer the given questions.
When Streptococcus pneumoniae bacteria are grown on a culture plate, some produce smooth shiny colonies while others produce rough colonies. This is because the S strain bacteria have a mucous coat, while R strain does not. Mice infected with the S strain die from pneumonia infection but mice infected with the R strain do not develop pneumonia. Griffith concluded that the R strain bacteria had somehow been transformed by the heat-killed S strain bacteria. Some ‘transforming principle’, transferred from the heat-killed S strain, had enabled the R strain to synthesise a smooth polysaccharide coat and become virulent. This must be due to the transfer of the genetic material. However, the biochemical nature of genetic material was not defined from his experiments.
DNA work as genetic material in all organisms because:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → DNA being more stable for storage of genetic information
A genetic material must be stable, so that it can store information without damage. RNA has a 2′-OH group on every nucleotide. This group is reactive, so RNA breaks down easily. DNA is chemically less reactive and structurally more stable, and thymine in place of uracil adds to its stability. So DNA is preferred for storing genetic information.
(1) DNA can be easily transformed — Incorrect. Transformation is the taking up of DNA by bacteria. It is not the reason why DNA is the genetic material, and a genetic material must not change easily.
(2) DNA being more stable for storage of genetic information — Correct. Stability is the reason DNA is the preferred genetic material.
(3) DNA mutates and evolve faster than RNA — Incorrect. The feature is reversed for the two. RNA is unstable and mutates faster, so RNA viruses evolve faster.
(4) DNA is made of ribonucleotides — Incorrect. DNA is made of deoxyribonucleotides. Ribonucleotides make RNA.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Properties of Genetic Material (DNA Versus RNA) – “… 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. 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 synthesising 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.”