Question

What is the nature of the 2 strands of a DNA duplex?

• A. Identical & Complimentary
• B. Antiparallel & complimentary
• C. Dissimilar & non complimentary
• D. Antiparallel & non complimentary

Answer 1

The correct option is B Antiparallel & complimentary

DNA is a macromolecule of high molecular weight made up of repeating units called nucleotides. Each nucleotide is made up of

1) a 5 carbon sugar

2) a phosphate group

3) a nitrogenous base.

DNA molecule is a helix with bases stacked perpendicularly to the main axis of the molecule. The two strands of a DNA, double helix are called complimentary due to specific base pairing, i.e, each chain has a sequence of nucleotides attached together by phosphodiester bonds joining the adjacent deoxyribose molecules. The base pairing,is specific as adenine is always paired with thymine and guanine with cytosine and vice-versa, i.e, one purine with another pyrimidine and one pyrimidine with another purine. This property of complimentarity makes DNA unique to store and transmit genetic information. The sugar-phosphate backbones of two complimentary strands are antiparallel as they have opposite chemical polarity. Therefore, one strand of the double helix has 5'-3' polarity while the other has 3'-5' polarity.