RIBONUCLEIC ACID

a single-stranded nucleic acid that encodes genetic information. RNA is made up of sequence of 4 chemical building blocks (nucleotides) -- adenine, cytosine, guanine and uracil. RNA is involved in the transcription of genetic information; the information encoded in DNA is translated into messenger RNA (mRNA), which controls the synthesis of new proteins. RNA takes the place of DNA in retroviruses such as HIV. The presence of HIV RNA in the plasma indicates that the virus is actively replicating.