DNA

DNA Deoxyribonucleic acid (DNA) is the hereditary unit in humans and the majority of living organisms. All living things contain DNA within their cells that hold the genetic instructions. In eukaryotes, most of the cellular DNA is located within a membrane-bound structure called the nucleus (which is referred to as nuclear DNA), but the mitochondria may also contain a small amount of DNA (which is referred to as mitochondrial DNA or mtDNA). In contrast, in prokaryotes, the genome is present in a region of the cytoplasm called the nucleoid as they do not contain any inner membranes. DNA is made of nucleotides. A nucleotide has two components: a backbone composed of alternating deoxyribose and phosphate groups, and each sugar is attached to one of four nitrogenous bases, known as adenine (A), cytosine (C), guanine (G), and thymine (T). DNA bases also pair up to form base pairs in which A is always paired with T and C is paired with G. About 3 billion bases are present in human DNA, and above 99 percent of human DNA is the same in the human population. Nucleotides are arranged in two long helices that are wrapped around each other to create a spiral called a double helix. A distinguishing characteristic of DNA is that it can make identical copies of itself which is defined as replication. Small sections of DNA, called genes, are used as codes for the synthesis of RNA and protein biomolecules that are required for the normal function of an organism. The complete set of genetic information contained within an organism is called its genome. The genome of a living organism is stored in chromosomes that are long molecules of DNA. Because of the tiny size of the cell, and because there are many DNA molecules inside a cell of each organism, each DNA molecule needs to be compact within the chromosome. Laboratory methods of genetic recombination (such as molecular cloning) use genetic material from multiple sources and bring them together to generate recombinant DNA (rDNA) molecules. [Tahirah Yasmin]

See also dna fingerprinting.