DNA STRUCTURE
Read the following passage carefully and answer the given questions.
DNA is a long polymer of deoxyribonucleotides. A nucleotide has three components – a nitrogenous base, a pentose sugar, and a phosphate group. There are two types of nitrogenous bases – Purines and Pyrimidines. DNA is made of two polynucleotide chains, where the backbone is constituted by sugar-phosphate, and the bases project inside. The bases in two strands are paired through hydrogen bond forming base pairs. As a result, always a purine comes opposite to a pyrimidine. This generates approximately uniform distance between the two strands of the helix. The plane of one base pair stacks over the other in double helix. This, in addition to H-bonds, confers stability of the helical structure. The two polynucleotide chains are coiled in a right-handed fashion. In eukaryotes, the DNA organisation is much more complex. There is a set of positively charged, basic proteins called histones. A protein acquires charge depending upon the abundance of amino acids residues with charged side chains.
Histones are rich in:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Lysine and arginine
Histones are positively charged, basic proteins. A protein gets its charge from the amino acids in it. The side chains of lysine and arginine carry positive charges. This lets histones bind the negatively charged DNA. Eight histone molecules form a histone octamer, and DNA is wrapped round it.
(1) Glycine and aspartic acid — Incorrect. Aspartic acid is acidic, with a negative charge. Glycine is a neutral amino acid.
(2) Lysine and arginine — Correct. Both are basic and positively charged.
(3) Isoleucine and asparagine — Incorrect. Neither carries a charge on its side chain.
(4) Methionine and alanine — Incorrect. Neither carries a charge on its side chain.
Note 1: 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.
Note 2: A similar question was also asked in CUET (UG) 2026 on 25-05-2026 (Slot 1), and in CUET (UG) 2025 on 22-05-2025 (Slot 2).
NCERT Extract:
Packaging of DNA Helix – “… In eukaryotes, this organisation is much more complex. There is a set of positively charged, basic proteins called histones. A protein acquires charge depending upon the abundance of amino acids residues with charged side chains. Histones are rich in the basic amino acid residues lysine and arginine.”