在所有生物體中構成基本遺傳物質的化合物。從結構上講，DNA是由兩條鏈相互纏繞構成彈簧狀結構稱為雙螺旋。每條鏈的主干是由脫氧核糖分子連接磷酸殘基形成，連在主干上的是稱為堿基的化學結構，它們從主干伸向螺旋結構的中央，有4種類型---腺嘌呤、胞嘧啶、鳥嘌呤和胸腺嘧啶（表示為A、C、G、T）。在DNA中C只能和G通過氫鍵連接，A只能和T連接，通過所謂氫鍵發生的這些作用將兩條鏈連在一起。每條DNA鏈的主干上都有一系列G、A、T、C。正是這些堿基序列構成密碼并被細胞翻譯成一個新的蛋白。另一條鏈（互補鏈或反義鏈）的序列總是與第一條鏈相匹配，即C與G，A與T，反過來也一樣。

The chemical that forms the basis of the genetic material in virtually all living organisms. Structurally, DNA is composed of two strands that intertwine to form a spring-like structure called the double helix. Each strand is formed by a backbone of deoxyribose sugar molecules linked by phosphate residues. Attached to each backbone are chemical structures called bases, which protrude away from the backbone towards the center of the helix, and which come in four types - Adenine, Cytosine, Guanine, and Thymine (designated A, C, G and T). In DNA a C can only hydrogen-bond with a G, and an A only with a T, these interactions, formed by so called hydrogen bonds, hold the two strands together. Each strand of DNA has a series of Gs, As, Ts and Cs attached to its backbone. It is the sequence of these bases that forms the code which is translated by cellular machinery to create a new protein. The other (complementary or antisense) strand always has a sequence that matches the first strand, with each C complemented by a G, and each A by a T, and vice versa.