Question

Which of these statements about eukaryotic DNA is incorrect?
I. It contains the complementary base pair A-U.
II. The two strands are antiparallel with 10 base pairs in each turn of the helix .
III. Number of purines is more than the number of pyrimidines.

• A. I and III
• B. II and III
• C. I and III
• D. I, II and III

Answer 1

The correct option is C I and III

The DNA has complementary base pairing where adenine forms double bonds with thymine and guanine forms triple bonds with cytosine. Adenine forming double bonds with uracil is seen in case of RNA.
According to Chargaff’s rule, the number of purines (A and G) is equal to the number of pyrimidines (C and T).
In DNA, two stands are antiparallel and each turn measuring 3.4 nm in length has approximately 10 base pairs present. The distance between two consecutive base pairs is about 0.34 nm.
Hence, I and III are incorrect statements while II is correct.