Read the passage given below and answer the following question.
Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the two types of nucleic acids found in living systems. DNA acts as the genetic material in most of the organisms. RNA though it also acts as a genetic material in some viruses, mostly functions as a messenger. RNA has additional roles as well. It functions as adapter, structural, and in some cases as a catalytic molecule. The chemical structure of a polynucleotide chain (DNA or RNA). A nucleotide has three components – a nitrogenous base, a pentose sugar (ribose in case of RNA, and deoxyribose for DNA), and a phosphate group. There are two types of nitrogenous bases – Purines and Pyrimidines.
Which of the following makes RNA labile and easily degradable compared to DNA?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Presence of a 2′-OH group in every nucleotide
DNA and RNA differ in their sugar. RNA has ribose, which carries an OH group at the 2′ carbon. DNA has deoxyribose, which lacks this OH. The 2′-OH is a reactive group, so it makes RNA labile (easily changed) and easily degradable. This is one reason why DNA, not RNA, is the main genetic material.
Option (1) Presence of thymine — Incorrect. Thymine is found in DNA, in place of uracil. The book says thymine gives DNA extra stability. RNA does not have thymine, so thymine cannot make RNA less stable.
Option (2) Presence of a 2′-OH group in every nucleotide — Correct. The 2′-OH group present at every nucleotide of RNA is reactive. It makes RNA labile and easily broken down.
Option (3) Presence of deoxyribose sugar — Incorrect. Deoxyribose is the sugar of DNA. Because it lacks the 2′-OH group, it makes DNA more stable, not RNA less stable.
Option (4) Presence of cytosine — Incorrect. Cytosine is present in both DNA and RNA. A base common to both cannot explain why RNA is less stable than DNA.
NCERT Extract:
Properties of Genetic Material (DNA versus RNA) – “… 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.”