Deoxyribonucleic acid (DNA) is a polymer made up of two polynucleotide chains that form a double helix. It carries genetic instructions for the development, functioning, growth, and reproduction of all known organisms and many viruses. DNA consists of nucleotides, each made of a nitrogenous base (cytosine [C], guanine [G], adenine [A], or thymine [T]), a sugar called deoxyribose, and a phosphate group. The strands are held together by hydrogen bonds between complementary bases (A with T, C with G) and have a sugar-phosphate backbone.
Most DNA (over 98% in humans) is non-coding, and both strands store the same information, which is replicated during cell division. Eukaryotic DNA is organized into chromosomes, stored in the nucleus, while prokaryotic DNA exists in circular chromosomes in the cytoplasm. DNA is transcribed into RNA, which specifies the sequence of amino acids in proteins through translation. Chromatin proteins, such as histones, help compact and organize DNA, influencing gene expression.
DNA is a long polymer made of repeating units called nucleotides and typically exists as two helical strands bound by hydrogen bonds, forming a double helix. These strands coil around the same axis with a pitch of 34 ångströms (3.4 nm) and a radius of 10 Å (1.0 nm). The backbone of DNA consists of alternating phosphate and sugar groups, specifically 2-deoxyribose. Nucleotides consist of a sugar, a phosphate, and a nucleobase, while the strand’s directionality is defined by its 3′ and 5′ ends. In contrast to RNA, which contains ribose instead of deoxyribose, DNA strands are antiparallel, meaning one strand runs in the opposite direction to the other.
