DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person's body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA). The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The sequence, or order, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.
DNA is not just a molecule but also a dynamic entity capable of self-replication and instruction for building the proteins that the body needs to function. Each DNA sequence that contains instructions to make a protein is known as a gene. The human genome contains around 20,000-25,000 genes. Besides coding for proteins, DNA also includes regions that regulate gene expression and areas that have structural or chromosomal maintenance roles. The process of DNA replication is crucial for cell division, allowing each new cell to have a complete set of DNA molecules.
The structure of DNA is referred to as a double helix, a term coined due to its spiral-staircase shape, consisting of two strands wound around each other. The sides of the staircase are made of alternating sugar (deoxyribose) and phosphate groups. Between these backbones are the pairing bases connected through hydrogen bonds, following the base-pairing rules: adenine pairs with thymine, and guanine pairs with cytosine. This arrangement allows for the base pairs to be perfectly positioned for the replication process, where enzymes break the hydrogen bonds between bases, allowing new complementary strands to be formed.
Advances in DNA technology have revolutionized fields such as forensic science, where DNA profiling has become a standard tool for solving crimes. Similarly, genetic testing and gene therapy are becoming increasingly common in medicine, offering new ways to diagnose, treat, and potentially cure genetic disorders. Research into DNA has also deepened our understanding of evolutionary biology, showing how genetic changes can influence the development of species over time. With ongoing research, the potential of DNA studies continues to expand, revealing new insights into both the history of life on Earth and possibilities for future biomedical advancements.