Question

Assertion (A): The sugar-phosphate backbone of two chains in DNA double helix show anti-parallel polarity.

Reason (R): The phosphor-diester 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.

Options

• Both (A) and (R) are true and (R) is the correct explanation of (A).

• Both (A) and (R) are true, but (R) is not the correct explanation of (A).

• (A) is true, but (R) is false.

• (A) is false, but (R) is true.

Answer 1

Both (A) and (R) are true and (R) is the correct explanation of (A).

Explanation:

The DNA double helix has an antiparallel configuration, with the sugar-phosphate backbones of the two strands orientated in opposing orientations. This indicates that one strand extends from 5' to 3', while the complementary strand extends from 3' to 5'. The phosphodiester linkages in each strand link the sugar of one nucleotide to the phosphate of the subsequent nucleotide, creating a continuous backbone.