Question
Biology Question on the molecular basis of inheritance
Which one of the following pairs of nitrogenous bases of nucleic acids, is wrongly matched with the category mentioned against it?
A
guanine, adenine - purines
B
adenine, thymine - purines
C
thymine, uracil - pyrimdines
D
uracil, cytosine - pyrimidines.
Answer
adenine, thymine - purines
Explanation
Solution
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'.