What is DNA?

DNA, or deoxyribonucleic acid, is the principal hereditary information molecule in cellular life. Information resides in nucleotide sequences and influences processes such as RNA and protein production. An organism’s characteristics cannot all be reduced to one sequence: gene activity and environmental interactions also matter.

DNA structure and organization

1. Double helix DNA usually consists of two complementary strands. Each nucleotide contains a sugar, phosphate and base. Adenine pairs with thymine and guanine with cytosine. Complementarity supports copying information, although DNA’s three-dimensional structure is more complex than a rigid ladder. 2. Genes, chromosomes and genomes Genes are DNA regions associated with producing functional RNA or proteins. Chromosomes comprise long DNA molecules and associated proteins. A genome is an organism’s complete genetic material. Not all DNA encodes proteins: regulatory regions and sequences with other functions also exist. 3. Cellular location In eukaryotes such as humans, most DNA is in the nucleus, with additional DNA in mitochondria. Bacteria lack a membrane-enclosed nucleus. DNA is therefore not located in the same cellular compartment in every organism.

Copying, expression and variation

4. Replication DNA is copied before cell division. Enzymes use existing strands as templates, producing double helices with one old and one new strand. Proofreading and repair reduce many errors without guaranteeing perfection. 5. Using the information Transcription produces RNA from DNA. For protein-coding genes, messenger RNA guides amino-acid assembly at ribosomes. Gene activity varies with cell type and conditions, allowing cells with the same DNA to perform different tasks. 6. Variation and research Sequence changes can have neutral, consequential or context-dependent effects. Many traits involve multiple genes interacting with the environment. Sequencing supports studies of biological relationships and other research, but one piece of genetic information does not determine an entire future with certainty.