With respect to structure of DNA, following four statements are made. Choose the two relevant statements.

(a) DNA is made of two long chains of nucleotides coiled in a helix around a central axis.

(b) DNA is made of two long chains of nucleoside coiled around a central axis.

(c) The two chains are complimentary to each other so that Adenine is always paired with Thymine and cytosine with Guanine.

(d) The two chains are not complimentary to each other where Adenine is paired with uracil and cytosine with Guanine.

The correct answer is Option 3.

Key Points

• (a) DNA is made of two long chains of nucleotides coiled in a helix around a central axis.
• (c) The two chains are complementary to each other so that Adenine is always paired with Thymine and Cytosine with Guanine.
• DNA consists of nucleotides, not nucleosides, making statement (b) irrelevant.
• Statement (d) is incorrect as it refers to pairing found in RNA (Adenine pairs with Uracil in RNA).
• Complementary base pairing is a defining feature of DNA structure, essential for replication and genetic coding.

Additional Information

• DNA (Deoxyribonucleic Acid) is a double-stranded molecule organized as a double helix.
• Each strand is made of a sugar-phosphate backbone and nitrogenous bases (Adenine, Thymine, Cytosine, Guanine).
• The strands are antiparallel, and the complementary base pairing is stabilized by hydrogen bonds.
• RNA (Ribonucleic Acid) differs from DNA as it is single-stranded and contains Uracil instead of Thymine.