  ribonucleic acid (rna) is a polymeric molecule. it is implicated in a varied sort of biological roles in coding, decoding, regulation, and expression of genes. dna and rna are nucleic acids, and, along with proteins and carbohydrates, constitute the three 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 unto itself, rather than a paired double-strand. cellular organisms use messenger rna (mrna) to convey genetic information (using the letters g, a, u, and c to denote the nitrogenous bases guanine, adenine, uracil and cytosine) that directs synthesis of specific proteins. many viruses encode their genetic information using an rna genome. 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 whereby mrna 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) links amino acids together to form proteins. ==comparison with dna== thumb|left|150px|bases in an rna molecule.  the chemical structure of rna is very similar to that of dna, but differs in three main ways: * unlike double-stranded dna, rna is a single-stranded molecule in many of its biological roles and has a much shorter chain of nucleotides. however, rna can, by complementary base pairing, form intrastrand double helixes, as in trna. * while dna contains deoxyribose, rna contains ribose (in deoxyribose there is no hydroxyl group attached to the pentose ring in the 2' position). these hydroxyl groups make rna less stable than dna because it is more prone to hydrolysis. * the complementary base to adenine is not thymine, as it is in dna, but rather uracil, which is an unmethylated form of thymine. like dna, most biologically active rnas, including mrna, trna, rrna, snrnas, and other non-coding rnas, contain self-complementary sequences that allow parts of the rna to fold{{cite jou
Biotechnology Molecular_biology RNA RNA_splicing