Ribonucleic Acid. A molecule essential in gene coding, decoding, regulation, and expression. Consists of sequences of the four nucleotide bases: Adenine, Uracil, Guanine, and Cytosine. Types of RNA include messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), small nuclear RNA (snRNA), and other non-coding RNAs. Some viruses including Influenza A and Sars-Cov-2 have RNA genomes.