Ribonucleic Acid

What is the Definition of Ribonucleic Acid?

Definition Knowing

According to AbbreviationFinder, Ribonucleic Acid is commonly known as RNA.

History

Nucleic acids were discovered in 1868 by Friedrich Miescher, who called them nuclein since he isolated them from the cell nucleus. Later, it was found that prokaryotic cells, lacking a nucleus, also contained nucleic acids. The role of RNA in protein synthesis was suspected in 1939. Severo Ochoa won the Nobel Prize in Medicine in 1959 after discovering how RNA was synthesized.

In 1965 Robert W. Holley found the sequence of 77 nucleotides of a yeast transfer RNA, which won him the Nobel Prize in Medicine in 1968. In 1967, Carl Woese verified the catalytic properties of some RNAs and suggested that the first Life forms used RNA as a carrier of genetic information as well as a catalyst for their metabolic reactions (RNA world hypothesis). In 1976, Walter Fiers and his collaborators determined the complete RNA sequence of the genome of an RNA virus (bacteriophage MS2).

In 1990 it was discovered in Petunia that introduced genes can silence similar genes from the same plant, leading to the discovery of interfering RNA. At around the same time, micro RNAs, small 22-nucleotide molecules that had some role in the development of Caenorhabditis elegans, were found. The discovery of RNAs that regulate gene expression has allowed the development of drugs made of RNA, such as small interfering RNAs that silence genes.

Chemical structure

Like DNA, RNA is made up of a chain of repeating monomers called nucleotides. The nucleotides are joined one after the other by negatively charged phosphodiester bonds.

Each nucleotide is made up of a five- carbon monosaccharide (pentose) molecule called ribose (deoxyribose in DNA), a phosphate group, and one of four possible nitrogenous compounds called bases: adenine, guanine, uracil (thymine in DNA), and cytosine.

Comparison between RNA and DNA
Aspects RNA DNA
pentose ribose Deoxyribose
Purinas Adenine and guanine Adenine and guanine
Pyrimidines Cytosine and Uracil Cytosine and Thymine

The ribose carbons are numbered 1 ‘to 5’ clockwise. The nitrogenous base binds to the 1 ‘carbon; the phosphate group is attached to the 5 ‘carbon and the 3’ carbon of ribose of the next nucleotide.

Phosphate has a negative charge at physiological pH, which gives RNA a polyanionic character. The puric bases (adenine and guanine) can form hydrogen bonds with the pyrimidines (uracil and cytosine) according to the C = G and A = U scheme, in addition, other interactions are possible, such as stacking of bases or tetraloops with G = pairings. TO.

Many RNAs contain, in addition to the usual nucleotides, modified nucleotides, which originate by transformation of the typical nucleotides; they are characteristic of transfer RNAs (tRNA) and ribosomal RNA (rRNA); methylated nucleotides are also found in eukaryotic messenger RNA.

Secondary structure

Unlike DNA, RNA molecules are single-stranded and do not usually form long double helices. However, it does fold as a result of the presence of short regions with intramolecular base pairing, that is, base pairs formed by more or less distant complementary sequences within the same strand.

TRNA has approximately 60% base paired in four arms with a double helix structure

An important structural feature of RNA that distinguishes it from DNA is the presence of a hydroxyl group in the 2 ‘position of ribose, which causes the RNA double helices to adopt an A conformation instead of the more common B conformation. in DNA This A helix has a very deep and narrow major groove and a wide and shallow minor groove.

A second consequence of the presence of said hydroxyl is that the phosphodiester bonds of RNA in regions where no double helix is ​​formed are more susceptible to chemical hydrolysis than those of DNA; RNA phosphodiester bonds hydrolyze rapidly in alkaline solution, while DNA bonds are stable. The half-life of RNA molecules is much shorter than those of DNA, a few minutes in some bacterial RNAs or a few days in humantRNAs.

Tertiary structure

The tertiary structure of RNA is the result of base stacking and hydrogen bonding between different parts of the molecule. TRNAs are a good example; in solution, they are folded into a compact “L” shape stabilized by conventional Watson and Crick pairings (A = U, C = G) and by base interactions between two or more nucleotides, such as base triplets; bases can donate hydrogen atoms to bind to the phosphodiester backbone; the OH of the 2 ‘carbon of ribose is also an important hydrogen donor and acceptor.

Biosynthesis

RNA biosynthesis is normally catalyzed by the enzyme RNA polymerase that uses a strand of DNA as a template, a process known as transcription. Therefore, all cellular RNAs come from copies of genes present in DNA.

Transcription begins with the recognition by the enzyme of a promoter, a characteristic sequence of nucleotides in DNA located before the segment to be transcribed; the double helix of DNA is opened by the helicase activity of the enzyme itself. The RNA polymerase then progresses along the DNA strand 3 ‘→ 5’, synthesizing a complementary RNA molecule; This process is known as elongation, and the growth of the RNA molecule occurs 5 ‘→ 3’.

The nucleotide sequence of DNA also determines where RNA synthesis ends, since it has characteristic sequences that RNA polymerase recognizes as termination signals.

After transcription, most RNAs are modified by enzymes. For example, to the newly transcribed eukaryotic pre-messenger RNA, a modified guanine nucleotide is added at the 5 ‘end, which is known as a “hood” or “cap”, and a long sequence of adenine nucleotides at the 3’ end (poly-A glue); subsequently the introns (non-coding segments) are eliminated in a process known as splicing.

In viruses, there are also several RNA-dependent RNA polymerases that use RNA as a template for the synthesis of new RNA molecules. For example, several RNA viruses, such as polioviruses, use these types of enzymes to replicate their genome.

Ribonucleic Acid