Glossary · Sinh học
DNA
The molecule that carries genetic information for the development and functioning of an organism. It has two strands wound around each other into a double helix, and the information lies in the sequence of four bases: A, C, G, T.
The two DNA strands wind around each other like a twisted ladder — the shape known as a double helix. Attached to each sugar is one of four bases: adenine (A), cytosine (C), guanine (G) or thymine (T).
Bases pair by a fixed rule: A with T, C with G. The A–T pair is held by two hydrogen bonds, the C–G pair by three. That pairing rule is what keeps the two strands matched.
The two strands are antiparallel: the 3' end of one faces the 5' end of the other. Watson and Crick proposed that DNA is made up of two strands twisted around each other into a right-handed helix. Each base pair is separated from the next by 0.34 nm and each turn of the helix measures 3.4 nm, so there are 10 base pairs per turn; the diameter of the double helix is 2 nm and is uniform throughout.