Nucleotides form chains
DNA chains consist of nucleotides containing deoxyribose, phosphate and a base. The common bases are abbreviated A, T, C and G. Information depends on their order rather than simply their quantities. Similar chemical building blocks can therefore form sequences with different biological functions along a sugar–phosphate backbone.
Complementarity and strand orientation
In the familiar double helix, A pairs with T and C with G, and the strands run in opposite chemical directions. One sequence constrains its complement, linking structure with copying. The ladder-like drawing is a model: DNA can also bend, coil and associate with proteins.
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Copying requires molecular machinery
Complementarity supplies a copying principle, but synthesis requires enzymes and other cellular components. Replication and repair promote faithful transmission without making mistakes impossible. Genetic material must be duplicated and distributed during division. Experimental work was needed to establish copying mechanisms rather than deducing every detail from a structural model.
Location and function in genomes
Most human DNA is in nuclear chromosomes, with a smaller amount in mitochondria. Genes can specify proteins or functional RNAs, while other regions have regulatory or different roles. Cells sharing DNA can behave differently because regulation and environment affect which information is used; sequence alone does not dictate every outcome.