DNA structure, function, and variations

DNA as a double helix polymer

DNA is a double helix polymer made of two intertwined polynucleotide chains that carry genetic instructions for living organisms and many viruses. Each chain is built from repeating nucleotides, and each nucleotide contains a deoxyribose sugar, a phosphate group, and one of four nitrogen-containing bases: adenine (A), thymine (T), cytosine (C), or guanine (G). The sugar and phosphate form an alternating backbone via phosphodiester linkages, while the bases project inward and pair across the helix using hydrogen bonds according to Watson–Crick rules (A with T, and C with G). Because the strands are complementary, both strands store the same information, and separating them enables replication. The two DNA strands run in opposite directions (antiparallel), with each strand having distinct 5′ and 3′ ends that confer directionality. The double helix is primarily stabilized by hydrogen bonding between paired bases and by base-stacking interactions between neighboring aromatic bases. DNA’s structure also includes major and minor grooves, which provide accessible binding sites for proteins that recognize specific DNA sequences. In cells, DNA is further organized into chromosomes (in eukaryotes) or circular chromosomes (in prokaryotes), and it can be compacted by proteins such as histones, while processes like transcription and replication depend on the double helix being locally unwound and separated.

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Nucleotides: bases, deoxyribose, phosphate

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