同DNA一起组成细胞遗传物质的一类核酸。DNA在细胞核中储存遗传信息，而RNA将DNA的信息带到细胞的其它部位，在那里指导蛋白质的合成。从结构来看，RNA是单链结构。构成RNA主体的复合糖是核糖（相反DNA是脱氧核糖），4个碱基是U、G、A、C（DNA以T代替U）。共有三种RNA，它们在把DNA信息转达给蛋白质过程中起到媒介作用：信使RNA是在核中的DNA复制，将信息带到解读密码的细胞机器所在的胞质中；转运RNA帮助每次读取3个碱基（一个密码子）并将信息由RNA转移至蛋白质；核糖体RNA是核糖体结构的一部分，核糖体是使RNA翻译为蛋白质的机器。

A category of nucleic acids which along with DNA forms the genetic material of a cell. While DNA stores the genetic information in the nucleus of every cell, RNA is a “carrier” of this information from DNA to other parts of the cell where the message is converted to protein. Structurally, RNA is a single-stranded structure. The component sugar that forms the backbone of RNA is ribose (as opposed to deoxyribose in DNA) and the four bases in RNA are Uracil, Guanine, Adenine and Cytosine (DNA contains Thymidine instead of Uracil). There are three types of RNA, all of which play an intermediary role in converting DNA information into protein: messenger RNA (mRNA) is a copy of the DNA in the nucleus and carries it to the cytoplasm where the cellular machinery for decoding that information lies; transfer RNA (tRNA) allows the code to be read three bases (one codon) at a time and transfers the information from RNA to protein (each tRNA carries one particular amino acid); and ribosomal RNA (rRNA) has a structural role forming part of the ribosome--the machinery that converts RNA into protein.