什么是去氧核糖核酸

deoxyribonucleic acid的缩写。

核酸的两种形式之一（另一种是核糖核酸）；分子结构复杂的有机化合物，见於所有的原核细胞、真核细胞及多种病毒中。DNA编码带有遗传讯息，决定着遗传性状的传递。1953年华生和克里克确定其分子结构为双条长链相互盘旋形成双螺旋的聚合物，每条链由一长串的单体核酸组成。而核酸是由一种带有磷酸的去氧核糖（戊糖）分子和一种含氮硷基构成。含氮硷基有四种︰腺嘌呤（A）、鸟嘌呤（G）、胞嘧啶（C）、胸腺嘧啶（T）。两条核酸链则靠硷基间的氢键相连；这种键合的次序是特定的，也就是腺嘌呤只与胸腺嘧啶结合，胞嘧啶只与鸟嘌呤结合。DNA复制时，双链分开，每条单链作为模板，按硷基间氢键配对的规则，将一个新硷基结合到原有的硷基上，构成一条新链。最後，产生了两个新的双链DNA分子，每个分子包含一条原有的DNA链和一条新链，这种形式的复制是遗传性状得以稳定继承的关键。所谓「基因」，指的就是DNA的一个片段，它编排了细胞内某种特定蛋白质的合成密码。DNA是以染色体（稠密的蛋白质-DNA复合体）形式存在於细胞中。真核细胞的染色体位於细胞核内，但在粒线体和叶绿体中也可发现DNA。有些原核细胞（如细菌）和一些真核细胞中有一种称为「质粒」的染色体外DNA结构，这是一种能独立自我复制的遗传物质。质粒现已广泛用於DNA重组技术中，以研究基因的表现方式。亦请参阅Franklin, Rosalind (Elsie)、genetic engineering、mutation、Wilkins, Maurice (Hugh Frederick)。

DNA

One of two types of nucleic acid (the other is RNA); a complex organic compound found in all living cells and many viruses. It is the chemical substance of genes. Its structure, with two strands wound around each other in a double helix to resemble a twisted ladder, was first described (1953) by Francis Crick and James D. Watson. Each strand is a long chain (polymer) of repeating nucleotides: adenine (A), guanine (G), cytosine (C), and thymine (T). The two strands contain complementary information: A forms hydrogen bonds (see hydrogen bonding) only with T; C only with G. When DNA is copied in the cell, the strands separate and each serves as a template for assembling a new complementary strand; this is the key to stable heredity. DNA in cells is organized into dense protein-DNA complexes (see nucleoprotein) called chromosomes. In eukaryotes these are in the nucleus, and DNA also occurs in mitochondria and chloroplasts (if any). Prokaryotes have a single circular chromosome in the cytoplasm. Some prokaryotes and a few eukaryotes have DNA outside the chromosomes in plasmids. See also Rosalind Franklin, genetic engineering, mutation, Maurice Wilkins.