<P> Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation, and expression of genes . RNA and DNA are nucleic acids, and, along with lipids, proteins and carbohydrates, constitute the four major macromolecules essential for all known forms of life . Like DNA, RNA is assembled as a chain of nucleotides, but unlike DNA it is more often found in nature as a single - strand folded onto itself, rather than a paired double - strand . Cellular organisms use messenger RNA (mRNA) to convey genetic information (using the letters G, U, A, and C to denote the nitrogenous bases guanine, uracil, adenine, and cytosine) that directs synthesis of specific proteins . Many viruses encode their genetic information using an RNA genome . </P> <P> Some RNA molecules play an active role within cells by catalyzing biological reactions, controlling gene expression, or sensing and communicating responses to cellular signals . One of these active processes is protein synthesis, a universal function where RNA molecules direct the assembly of proteins on ribosomes . This process uses transfer RNA (tRNA) molecules to deliver amino acids to the ribosome, where ribosomal RNA (rRNA) then links amino acids together to form proteins . </P> <P> The chemical structure of RNA is very similar to that of DNA, but differs in three main ways: </P>

Rna dictates the structure of a protein in a process known as