RNA stands for ribonucleic acid; the critical, chemical "middle-man" for translating genetic information.
Like DNA, RNA consists of a backbone of sugar and phosphate fused to a sequence of bases. Unlike DNA, which has deoxy-ribose in its backbone, the sugar in RNA's backbone is ribose. In addition, the base T (thymine) in DNA is replaced by U (uracil) in RNA.
One of the most important differences between DNA and RNA is that RNA exists only a single strand rather than as a double helix. RNA mediates the expression of genetic information permantly stored in DNA.
There are three major kinds of RNA: