Ribonucleic acid is similar in structure to deoxyribonucleic acid (DNA). However, it plays only a minor role as a carrier of genetic information. As an intermediate store of information, it serves, among other functions, as a translator and transmitter of the genetic code from DNA to protein.
What is ribonucleic acid?
Abbreviated in both English and German, ribonucleic acid is called RNA. It is similar in structure to DNA (deoxyribonucleic acid). Unlike DNA, however, it consists of only one strand. Its task is, among other things, the transmission and translation of the genetic code during protein biosynthesis. However, RNA occurs in different forms and also fulfills different tasks. Shorter RNA molecules do not have a genetic code at all, but are responsible for transporting certain amino acids. Ribonucleic acid is not as stable as DNA because it has no long-term storage function for the genetic code. In the case of mRNA, for example, it merely serves as a temporary storage until the transfer and translation is complete.
Anatomy and structure
Ribonucleic acid is a chain composed of many nucleotides. The nucleotide consists of a compound between phosphate residue, sugar and nitrogen base. The nitrogen bases adenine, guanine, cytosine and uracil are each attached to a sugar residue (the ribose). The sugar, in turn, is esterified with a phosphate residue in two places and forms a bridge with the latter. The nitrogen base is located at the opposite position of the sugar. Sugar and phosphate residues alternate and form a chain. The nitrogen bases are thus not directly linked to each other, but are located on the side of the sugar. Three nitrogen bases in a row are called a triplet and contain the genetic code for a specific amino acid. Several triplets in a row encode a polypeptide or protein chain. Unlike DNA, the sugar contains a hydroxyl group at the 2′ position instead of a hydrogen atom. In addition, the nitrogen base thymine is exchanged for uracil in RNA. Because of these minor chemical differences, RNA, unlike DNA, generally occurs only in a single strand. The hydroxyl group in ribose also ensures that ribonucleic acid is not as stable as DNA. Its assembly and disassembly must be flexible because the information to be transferred is constantly changing.
Function and tasks
Ribonucleic acid performs several tasks. As a long-term storage for the genetic code, it is usually out of the question. Only in some viruses does RNA serve as a carrier of genetic information. In other organisms, this task is performed by DNA. Among other things, RNA acts as a transmitter and translator of the genetic code in protein biosynthesis. The mRNA is responsible for this. Translated, mRNA means messenger RNA. It copies the information found on a gene and transports it to the ribosome, where a protein is synthesized with the help of this information. In the process, three adjacent nucleotides form a so-called codon, which represents a specific amino acid. In this way, a polypeptide chain of amino acids is built up step by step. The individual amino acids are transported to the ribosome by means of tRNA (transfer RNA). In this process, the tRNA thus functions as an auxiliary molecule in protein biosynthesis. As another RNA molecule, rRNA (ribosomal RNA) is involved in the assembly of ribosomes. Other examples include asRNA (antisense RNA) for regulating gene expression, hnRNA (heterogeneous nuclear RNA) as a precursor to mature mRNA, ribowitches for gene regulation, ribozymes for catalyzing biochemical reactions, and many more. The RNA molecules may not be stable because different transcripts are needed at different times. The cleaved nucleotides or oligomers are constantly used to re-synthesize RNA. According to Walter Gilbert’s RNA world hypothesis, RNA molecules formed the precursors of all organisms. Even today, they are the sole carriers of the genetic code in some viruses.
Diseases
In the context of disease, ribonucleic acids play a role in that many viruses have only RNA as their genetic material. Thus, in addition to DNA viruses, there are also viruses with single- or double-stranded RNA. Outside of a living organism, a virus is completely inactive. It has no metabolism of its own.However, when a virus comes into contact with body cells, the genetic information of its DNA or RNA is activated. The virus begins to reproduce itself with the help of the host cell’s organelles. In the process, the host cell is reprogrammed by the virus to produce individual virus components. The genetic material of the virus enters the cell nucleus. There, its incorporation into the DNA of the host cell takes place, and new viruses are constantly produced. The viruses are discharged from the cell. The process repeats until the cell dies. In RNA viruses, the enzyme reverse transcriptase is used to transcribe the genetic information of the RNA into the DNA. Retroviruses are a special form of RNA viruses. For example, the HI virus is one of the retroviruses. In retroviruses, too, the enzyme reverse transcriptase ensures the transfer of the genetic information of the single-stranded RNA into the DNA of the host cell. New viruses are generated there, which leave the cell without being destroyed. New viruses are always being formed, which constantly infect other cells. Retroviruses are very mutative and therefore difficult to combat. A combination of several components such as reverse transcriptase inhibitors and protease inhibitors is used as therapy.
