Deoxyribonucleic acid (DNA) is the hereditary material in almost all organisms, carrying genetic instructions for growth, development, and reproduction. It is built from nucleotides that form two complementary strands wound around each other in a double helix. The sequence of its four bases—adenine, thymine, cytosine, and guanine—encodes information that cells use to make proteins.
## Explanation
DNA is organised into long molecules called chromosomes, which are packaged around proteins called histones to fit inside cells. Each strand runs in opposite directions, and the specific pairing of adenine with thymine and cytosine with guanine allows DNA to replicate itself when cells divide【835337830232644†L76-L100】. During replication, enzymes unwind the double helix and use each strand as a template to build a complementary strand. Genes are specific segments of DNA that provide instructions for making RNA and proteins. The flow of information from DNA to RNA to protein is central to biology. The human genome contains about three billion base pairs distributed among 23 pairs of chromosomes. Smaller circular DNA molecules are found in mitochondria, where they encode proteins needed for energy production. DNA is subject to mutations, which create genetic variation and can lead to inherited disorders if they occur in critical genes. Cells have repair mechanisms to fix damage from radiation or chemicals.
## Notable points and uses
DNA typing has become essential in medicine, research, and forensic science. Sequencing genomes helps identify genes involved in disease, trace ancestry, and understand evolutionary relationships. Recombinant DNA technology allows scientists to insert genes into organisms to produce medicines like insulin. Polymerase chain reaction (PCR) uses DNA polymerase to amplify specific sequences, enabling rapid detection of pathogens. DNA profiling is used in criminal investigations to link biological samples to individuals. In agriculture, genetic information guides selective breeding and the development of crops resistant to pests or drought.
DNA’s stability and ability to replicate make it ideal for storing genetic information. It underlies heredity and evolution and has wide applications in science and society.
**Related Terms:** Gene, Chromosome, RNA, Genome, Mutation