RNA, for ribonucleic acid, is a nucleic acid that is chemically similar to DNA. It is a polymer of nucleotides consisting of a ribose sugar, a phosphate and bases such as adenine, guanine, cytosine and uracil. It is found in all living things and also in some viruses. RNA plays an essential role in gene expression by acting as a temporary carrier of genetic information. RNA acts as an intermediary between the genetic information encoded by DNA and proteins. But it also has other functions such as the regulation of gene expression, enzyme catalysis and enzyme guidance.

The term total RNA encompasses the three main types of RNA: messenger RNA (mRNA), ribosomal RNA (rRNA) and transfer RNA (tRNA). The mRNA represents 5% of total RNA, it carries the genetic code copied from the DNA and serves as a temporary carrier. Ribosomal RNAs are found in ribosomes and represent 80% of total RNAs. The rRNAs combine with proteins and enzymes in the cytoplasm of the cell to form ribosomes, which act as a site for protein synthesis. These complex structures move along the mRNA molecule during translation. Transfer RNA is the smallest of the 3 types of RNA and its main role is the transfer of amino acids during protein synthesis.