Class 12 NEET Biology Molecular Basis of Inheritance Questions Part 1

The two DNA chains are held together by hydrogen bonds between their nitrogenous bases. Adenine (A), a purine of one chain lies exactly opposite thymine (T), a pyrimidine of the other chain. Similarly, cytosine (C), a pyrimidine lies opposite guanine (G), a purine.
Three hydrogen bonds occur between cytosine and guanine (C - G) at positions 1′ 2′ and 6′ and two hydrogen bonds between adenine and thymine A−T at positions 1′ and 6′