According to abbreviationfinder, the ribonucleic acid (RNA) -from English ribonucleic acid or RNA ) is a nucleic acid comprising a chain of ribonucleotides. It is present in both prokaryotic and eukaryotic cells, and is the only genetic material of certain viruses (RNA viruses). Cellular RNA is linear and single-stranded, but in the genome of some viruses it is double-stranded.
In cellular organisms it performs several functions. It is the molecule that directs the intermediate stages of protein synthesis; DNA cannot act alone, and uses RNA to transfer this vital information during protein synthesis (the production of the proteins the cell needs for its activities and development). Several types of RNA regulate gene expression, while others have catalytic activity. RNA is thus much more versatile than DNA.
DNA is the carrier molecule for genetic information in all cellular organisms, but like DNA, RNA can store genetic information. RNA viruses are completely devoid of DNA and their genome is made up of RNA, which encodes the proteins of the virus, such as those of the capsid and some enzymes. These enzymes carry out the replication of the viral genome. Viroids are another type of pathogen that consists exclusively of an RNA molecule that does not encode any protein and that is replicated by the host cell’s machinery.
RNA world hypothesis
The RNA world hypothesis proposes that RNA was the first life form on Earth, subsequently developing a cell membrane around it and thus becoming the first cell. It is based on the verification that RNA can contain genetic information, in a way analogous to DNA, and that some types are capable of carrying out metabolic reactions, such as self-cutting or formation of peptide bonds.
For years it was speculated which came first, DNA or enzymes, since enzymes are synthesized from DNA and DNA synthesis is carried out by enzymes. If it is assumed that the first forms of life used RNA both to store their genetic information and to carry out their metabolism, this stumbling block is overcome. Experiments with basic ribozymes, such as viral Q-beta RNA, have shown that simple self-replicating RNA structures can withstand even strong selective pressures (such as chain terminators of opposite chirality).
RNA with catalytic activity
Transformation of uridine into pseudouridine, a common RNA modification.
- Ribozymes. RNA can act as a biocatalyst. Certain RNAs associate with proteins forming ribonucleoproteins and it has been found that it is the RNA subunit that carries out the catalytic reactions; these RNAs perform the reactions in vitro in the absence of protein. Five types of ribozymes are known; three of them carry out self-modification reactions, such as intron removal or self-cutting, while the others (ribonuclease P and ribosomal RNA) act on different substrates. Thus, ribonuclease P cuts a precursor RNA into tRNA molecules, while ribosomal RNA makes the peptide bond during ribosomal protein synthesis.
- Spiceosome. Introns are separated from pre-mRNA during the process known as splicing by splices, which contain numerous small nuclear RNAs (pRNA or snRNA). In other cases, the introns themselves act as ribozymes and separate themselves from the exons.
- Small nucleolar RNA. Small nucleolar RNAs (pnoRNA or snoRNA), found in the nucleolus and Cajal bodies, direct the modification of nucleotides of other RNAs; the process consists of transforming one of the four typical nitrogenous bases (A, C, U, G) into others. PRNAs associate with enzymes and guide them by pairing with specific sequences of the RNA they will modify. RRNAs and tRNAs contain many modified nucleotides.