Molecular Basis of Inheritance Question 131
131. In the DNA molecule
[2008]
(a) the total amount of purine nucleotides and pyrimidine nucleotides is not always equal
(b) there are two strands which run parallel in the $5^{\prime} \to 3^{\prime}$ direction
(c) the proportion of Adenine in relation to thymine varies with the organism
(d) there are two strands which run anti parallel one in $5^{\prime} \to 3^{\prime}$ direction and other in $3^{\prime} \to 5^{\prime}$
Show Answer
Answer : d
Hints & Solution
(d) In the DNA molecule, there are two strands which run anti parallel, one is $5^{\prime}-3^{\prime}$ direction and other in 3’-5’ direction. The two strands are held together by hydrogen bonds between their bases. Adenine (A), a purine of one chain is exactly opposite to thymine (T), a pyrimidine of the other chain. Similarly, cytosine (C), a pyrimidine lies opposite to guanine (G), a purine. This allows a sort of lock $&$ key arrangment between large sized purine & small sized pyrimidine. It is strengthened by the appearance of hydrogen bonds between the two.
