DNA
DNA, or deoxyribonucleic acid, is the molecule that stores hereditary instructions in cells and many viruses. Its double-helix structure, base pairing, and organization into genes and chromosomes let organisms copy information, pass it on, and use it to build proteins.
What DNA is
DNA is a long biological molecule that stores information in the order of its chemical bases. It is found in living cells and in many viruses. In cells, DNA is the durable reference copy that can be replicated before division and read when a cell needs to make RNA or proteins.
Nucleotides and bases
A DNA strand is built from nucleotides. Each nucleotide contains a deoxyribose sugar, a phosphate group, and one nitrogenous base. The four standard DNA bases are adenine, thymine, guanine, and cytosine, often shortened to A, T, G, and C.
The double helix
DNA is usually described as a double helix: two strands winding around each other like a twisted ladder. The sugar-phosphate backbones form the outside rails, while paired bases form the rungs. The strands run in opposite directions, which matters for replication, repair, and transcription.
Genes, chromosomes, and genomes
A gene is a DNA sequence that contributes to a functional product, often a protein or RNA. In eukaryotic cells, DNA is packaged with proteins into chromosomes inside the nucleus, with additional DNA in mitochondria and, in plants and algae, chloroplasts. The complete DNA set is called a genome.
How DNA stores information
DNA stores information through base sequence. A protein-coding gene is transcribed into RNA, and that RNA can be translated into an amino acid sequence. Much DNA does not directly code for proteins, but it can influence when genes turn on, how much RNA is made, and how chromosomes are maintained.
Replication and repair
Before a cell divides, DNA must be copied. The two strands separate, and each serves as a template for a new complementary strand. Cells also use repair systems to fix many kinds of DNA damage, because copying errors or chemical damage can change sequence information.
Mutation and variation
A mutation is a change in DNA sequence or structure. Some mutations have little effect, some are harmful, and some contribute to useful variation over generations. Insertions, deletions, base substitutions, duplications, and chromosome rearrangements can all alter genetic information.
Sequencing and biotechnology
DNA sequencing reveals the order of bases in DNA. That ability supports medicine, ancestry research, conservation, forensics, agriculture, and basic biology. Biotechnology also uses DNA through cloning, synthetic biology, CRISPR-based editing, diagnostic tests, and engineered organisms.
Why it matters
DNA gives biology a memory system. It links inheritance, development, evolution, disease risk, and biotechnology in one molecule. Understanding DNA makes it easier to understand RNA, proteins, enzymes, genetics, evolution, and why small molecular changes can echo across an organism.