Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Among the two nucleic acids, DNA is preferred for the storage of genetic information.
Reason (R): RNA can directly code for the synthesis of proteins, whereas DNA is dependent on RNA for the synthesis of proteins.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both (A) and (R) are true but (R) is not the correct explanation of (A).
Both DNA and RNA can act as genetic material, but they suit different jobs. A molecule that stores genetic information must stay unchanged for a long time, so stability matters most. A molecule that expresses the information must be able to make proteins quickly.
Assertion (A): Among the two nucleic acids, DNA is preferred for the storage of genetic information. — True. DNA is chemically less reactive and structurally more stable than RNA. RNA has a reactive 2′-OH group on every nucleotide, which makes it labile and easily degraded.
Reason (R): RNA can directly code for the synthesis of proteins, whereas DNA is dependent on RNA for the synthesis of proteins. — True. The protein-making machinery has evolved around RNA, so RNA can easily express characters, while DNA has to work through RNA.
Why R does not explain A? A is about storage, and DNA wins there because of its stability. R is about expression, and it shows an advantage of RNA, not of DNA. A point in favour of RNA cannot be the reason why DNA is preferred. So both statements are correct, but R is not the explanation of A.
NCERT Extract:
Properties of Genetic Material (DNA versus RNA) – “… 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.”
Properties of Genetic Material (DNA versus RNA) – “… 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. For the transmission of genetic information, RNA is better.”