Question

Assertion :The sugar phosphate backbone of two chains in DNA double helix show anti-parallel polarity. Reason: The phosphodiester bonds in one strand go from a 3 carbon of one nucleotide to a 5 carbon of adjacent nucleotide, whereas those in complementary strand go vice versa.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

The backbone of a DNA chain or strand is built up of alternate deoxyribose sugar and phosphoric acid groups. The phosphate group is connected to carbon 5 of the sugar residue of its own nucleotide and carbon 3 of the sugar residue of the next nucleotide by (3 → 5) phosphodiester bonds. The two DNA chains are antiparallel, that is, they run parallel but in opposite directions.

In one chain the direction is 5 → 3, while in the opposite one, it is 3 → 5.

So, the correct answer is 'Both Assertion and Reason are correct and Reason is the correct explanation for Assertion'.