The correct answer is (3) Nucleotides.
DNA’s double-helix structure forms from two antiparallel strands of a linear polymer, where each strand consists of repeating nucleotide subunits linked by phosphodiester bonds.

Option Analysis

Nucleic acids: These are the broader class of macromolecules (DNA or RNA) built from nucleotide polymers, not the subunits themselves. Incorrect, as nucleic acids represent the complete polymer.

Amino acids: These are protein building blocks, forming peptide chains unrelated to DNA’s sugar-phosphate backbone and bases. Incorrect for DNA structure.​

Nucleotides: Correct. Each nucleotide has a deoxyribose sugar, phosphate group, and nitrogenous base (A, T, C, G), stacking to form the helix via base pairing.

Carbohydrates: These provide energy or structure (e.g., cellulose), not genetic polymers like DNA. Incorrect.​

The double helix structure of DNA is a linear polymer comprised of subunits called nucleotides, forming the blueprint of life as discovered by Watson and Crick in 1953. This twisted ladder shape relies on nucleotide monomers for stability and replication.

Nucleotide Composition

Nucleotides consist of a deoxyribose sugar, phosphate, and one of four bases: adenine (A), thymine (T), cytosine (C), or guanine (G). These link via 5′-3′ phosphodiester bonds, creating antiparallel strands held by hydrogen bonds (A-T, C-G). In B-DNA, ~10.5 base pairs turn per helix with major/minor grooves for protein binding.

Why Not Other Options?

Nucleic acids are the full polymer, amino acids build proteins, and carbohydrates store energy—none form DNA’s backbone. Nucleotides uniquely enable base pairing and semiconservative replication.

Ideal for NEET, GATE Life Sciences, or botany exams, this concept tests molecular biology basics.​