Ribonucleic acid ( RNA ) is an important polymeric molecule in a variety of biological roles in coding, decomposition, regulation, and gene expression. RNA and DNA are nucleic acids, and, together with lipids, proteins and carbohydrates, are the four major macromolecules important to all known life forms. Like DNA, RNA is assembled as a nucleotide chain, but unlike DNA, RNA is more commonly found in nature as a single strand that is folded into itself, rather than a paired double strand. Cellular organisms use messenger RNA ( mRNA ) to convey genetic information (using guanine nitrogenous bases, uracil, adenine and cytosine, denoted by the letters G, U, A, and C) that directs the synthesis of specific proteins. Many viruses encode their genetic information using the RNA genome.
Some RNA molecules play an active role in 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 in which RNA molecules direct the assembly of proteins to the ribosome. This process uses the transfer of RNA ( tRNA ) molecules to send amino acids to the ribosome, where ribosomal RNA ( rRNA ) then connect the amino acids together to form proteins.
Video RNA
Comparison with DNA
Like DNA, most RNAs are biologically active, including mRNA, tRNA, rRNA, snRNA, and other non-coding RNAs, containing complementary sequences that allow the RNA section to fold and coalesce with itself to form a double helix. This RNA analysis has revealed that they are highly structured. Unlike DNA, the structure does not consist of a long double helix, but a collection of short helices that are packed together into structures similar to proteins. In this way, RNA can achieve chemical catalysis (such as enzymes). For example, the determination of the ribosome structure - an RNA protein complex that catalyzes the formation of peptide bonds - reveals that the active site is composed entirely of RNA.
Maps RNA
Structure
Each nucleotide in RNA contains ribose sugar, with carbon numbered 1 'to 5'. The base attaches to position 1 ', in general, adenine (A), cytosine (C), guanine (G), or uracil (U). Adenine and guanine are purine, cytosine and uracil are pyrimidines. A phosphate group is attached to the 3 'position of one ribose and position 5' of the next. The phosphate group has its own negative charge, making RNA a charged molecule (polyanion). Bases form hydrogen bonds between cytosine and guanine, between adenine and uracil and between guanine and uracil. However, other interactions are possible, such as a group of adenine bases that bind to each other in a bulge, or GNRA tetraloop that has a guanine-adenine base pair.
An important structural component of RNA that distinguishes it from DNA is the presence of a hydroxyl group at the 2 'position of the ribose sugar. The presence of this functional group causes the helix to largely take the A-shape geometry, although in the context of single-stranded dinucleotides, RNA can seldom also adopt the most commonly observed B-shapes in DNA. A-shape geometry produces a very large deep groove and narrow and small grooves are shallow and wide. A second consequence of the presence of the 2'-hydroxyl group is that in the flexible regions of the RNA molecule (ie, not involved in the formation of double helix), it can chemically attack adjacent phosphodiester bonds to split the spine.
RNA is transcribed with only four bases (adenine, cytosine, guanine, and uracil), but these attached bases and sugars can be modified in various ways as RNA matures. Pseudouridine (?), Where the relationship between uracil and ribose is changed from the C-N bond to the C-C bond, and ribothymidine (T) is found in various places (most importantly in the TREC tRNA loop). Another well-known modification base is hypoxanthine, a degraded adenine base whose nucleosides are called inosine (I). Inosin plays a key role in the faltering hypothesis of the genetic code.
There are more than 100 other naturally occurring modified nucleosides. The greatest diversity of structural modifications can be found in tRNAs, while pseudouridine and nucleoside with 2'-O-methylribose often present in rRNA are the most common. The specific role of many of these modifications in RNA is not fully understood. However, it should be noted that, in ribosomal RNA, many post-transcriptional modifications occur in highly functional areas, such as peptidil transfer centers and subunit interfaces, implying that they are important for normal functioning.
The functional form of single-stranded RNA molecules, like proteins, often requires certain tertiary structures. The scaffold for this structure is provided by secondary structural elements which are the hydrogen bonds in the molecule. This causes some recognizable "domain" secondary structures such as hairpin loops, bumps, and internal loops. Because RNA is charged, metal ions such as Mg 2 are needed to stabilize many secondary and tertiary structures.
The natural enantiomer of RNA is D -RNA consists of D -ribonucleotides. All the chirality centers are located at D -ribose. By using L -taking or rather L -ribonucleotides, L -RNA can be synthesized. L -RNA is much more stable against degradation by RNase.
Like other structured biopolymers such as proteins, one can define the folded RNA molecular topology. This is often done based on the arrangement of intra-chain contacts in a folded RNA, referred to as circuit topology.
Synthesis
RNA synthesis is usually catalyzed by enzymes - RNA polymerase - using DNA as a template, a process known as transcription. The initiation of transcription begins with binding of the enzyme to the promoter sequence in DNA (usually found "upstream" of the gene). The double helix of DNA is released by enzyme helicase activity. Enzymes then develop along the mold strand in the 3 'to 5' direction, synthesizing complementary RNA molecules with an extension occurring in directions 5 'to 3'. The DNA sequence also determines where the termination of RNA synthesis will occur.
RNAs of primary transcripts are often modified by enzymes after transcription. For example, the tail of poly (A) and cap 5 'is added to the eukaryotic pre-mRNA and the intron is removed by the spliceosome.
There are also a number of RNA-dependent RNA polymerases that use RNA as a template for the synthesis of new strands of RNA. For example, a number of RNA viruses (such as polio viruses) use this type of enzyme to replicate their genetic material. Also, RNA-dependent RNA polymerase is part of the RNA interference pathway in many organisms.
RNA type
Overview
Messenger RNA (mRNA) is an RNA that carries information from DNA to ribosomes, the sites of protein synthesis (translation) within cells. The mRNA coding sequence determines the amino acid sequence in the resulting protein. However, many RNAs do not encode proteins (about 97% of the transcription output is non-protein-coding in eukaryotes).
The so-called non-coding RNA ("ncRNA") can be encoded by their own genes (RNA genes), but can also be derived from intron mRNAs. The most notable example of non-coding RNA is the transfer of RNA (tRNA) and ribosomal RNA (rRNA), both of which are involved in the translation process. There is also non-coding RNA involved in gene regulation, RNA processing and other roles. Certain RNAs can catalyze chemical reactions such as cutting and binding other RNA molecules, and catalysis of peptide bond formation in ribosomes; these are known as ribozymes.
Length
According to the length of the RNA chain, RNA includes small RNA and long RNA. Typically, a small RNA is shorter than 200Ã, nt in length, and RNA is longer than 200 nt long. Long RNAs, also called large RNAs, mainly include long-coded non-coding RNA (lncRNA) and mRNA. Small RNAs mainly include 5.8S ribosomal RNA (rRNA), 5S rRNA, RNA transfer (tRNA), microRNA (miRNA), small mixed RNA (siRNA), small nucleolar RNA (snoRNA), Piwi-interacting RNA (piRNA), tRNA - small RNA derivatives (tsRNA) and inferred small RNA RNA (srRNA).
In translation
Messenger RNA (mRNA) carries information about the protein sequence to the ribosome, the protein synthesis plant within the cell. It is encoded so that every three nucleotides (codons) correspond to one amino acid. In eukaryotic cells, once the mRNA precursor (pre-mRNA) has been transcribed from the DNA, it is processed into mature mRNA. This removes its intron - the non-coding part of pre-mRNA. The MRNA is then exported from the nucleus to the cytoplasm, where it is bound to the ribosome and translated into a form of protein corresponding to the aid of a tRNA. In prokaryotic cells, which have no nuclear compartment and cytoplasm, mRNAs may bind to the ribosome while being transcribed from DNA. After some time, the message decreases to its component nucleotides with the help of ribonuclease.
Transfer of RNA (tRNA) is a small RNA chain of about 80 nucleotides that transfer certain amino acids to the polypeptide chain grown on the ribosomal site of protein synthesis during translation. It has sites for amino acid attachments and anticodon areas for the introduction of codons that bind to a specific sequence on messenger RNA chains through hydrogen bonding.
Ribosomal RNA (rRNA) is the catalytic component of the ribosome. Eukaryotic ribosomes contain four different rRNA molecules: 18S, 5.8S, 28S and 5SRRNA. Three rRNA molecules are synthesized in the nucleolus, and one is synthesized elsewhere. In the cytoplasm, RNA and ribosome proteins combine to form a nucleoprotein called ribosomes. Ribosome binds mRNA and performs protein synthesis. Some ribosomes can be attached to a single mRNA at any time. Almost all RNAs found in typical eukaryotic cells are rRNAs.
RNA-messenger transfers (tmRNAs) are found in many bacteria and plastids. This protein tag is encoded by mRNA that does not stop the codon for degradation and prevents the ribosome from stalling.
RNA Rule
Several types of RNA can decrease the regulation of gene expression by being a complementary part of mRNA or DNA genes. MicroRNAs (miRNA; 21-22tt) are found in eukaryotes and act by RNA interference, in which the miRNA-effector complexes and enzymes can bypass complementary mRNAs, block mRNAs from being translated, or accelerate degradation.
While the small mixed RNA (siRNA; 20-25Ã, nt) is often generated by viral RNA splitting, there is also an endogenous source of siRNA. siRNA acts through RNA interference in the same way as miRNA. Some miRNAs and siRNAs can cause genes they target to be methylated, thereby reducing or increasing the transcription of these genes. Animals have Piwi-interacting RNAs (piRNAs; 29-30a nt) that are active in germline cells and are considered as defense against transposons and play a role in gametogenesis.
Many prokaryotes have CRISPR RNA, a regulatory system similar to RNA interference. RNA antisense is widespread; mostly degrading a gene, but some are activators of transcription. One way RNA antisense can act is by binding to mRNA, forming an enzymatic degradable double strand of RNA. There are many long noncoding RNAs that regulate genes in eukaryotes, one of which RNA is the Xist, which coats one X chromosome in a female mammal and disables it.
An mRNA may contain the element of the arrangement itself, such as the riboswitch, in the untranslated 5 'region or 3' non-translated region; these c-arrangement elements regulate the activity of the mRNA. Areas that are not translated can also contain elements that govern other genes.
In RNA processing
Many RNAs are involved in modifying other RNAs. Intron is spliced ​​out of pre-mRNA by spliceosomes, which contain several small nuclear RNAs (snRNAs), or introns can be ribozymes attached by themselves. RNA can also be converted with nucleotides modified into nucleotides other than A, C, G and U. In eukaryotes, modification of nucleotide RNA is generally directed by small nuclear RNA (snoRNA; 60-300 Â ° nt), found in nucleolus. and body cajal. SnoRNA associates with enzymes and guides them to a point on RNA with basepairing to the RNA. This enzyme then modifies the nucleotides. rRNAs and tRNAs are widely modified, but snRNA and mRNA can also be the basic modification targets. RNA can also be methylated.
RNA genome
Like DNA, RNA can carry genetic information. RNA virus has a genome consisting of RNA that encodes a number of proteins. Viral genomes are replicated by some of these proteins, while other proteins protect the genome when virus particles move into new host cells. Viroids are another group of pathogens, but they only consist of RNA, do not encode any protein and are replicated by host plant cell polymerases.
In reverse transcript
Reversing virus transcription replicates their genome by copying a copy of the inverse DNA from their RNA; a copy of this DNA is then transcribed to a new RNA. Retrotransposons also spread by copying DNA and RNA from each other, and telomerase contains RNA that is used as a template to build the ends of eukaryotic chromosomes.
Double-stranded RNA
Double-stranded RNA (dsRNA) is an RNA with two complementary strands, similar to DNA found in all cells. dsRNA forms the genetic material of several viruses (double-stranded RNA virus). Double-stranded RNAs such as viral RNA or siRNA can trigger RNA interference in eukaryotes, as well as interferon responses in vertebrates.
RNA Circular
In the late 1970s, it was shown that there was a circular closed covalent, i.e. the circular form of RNA expressed throughout the animal kingdom and plants (see circRNA). circRNAs allegedly arise through a back-splice reaction in which the spliceosome joins the downstream donor to the upstream acceptor sausage site. So far the circulatory function is not well known, although for some instances the activity of sponging microRNA has been demonstrated.
Key discoveries in biological RNA
Research on RNA has produced many important biological discoveries and many Nobel Prizes. Nucleic acid was discovered in 1868 by Friedrich Miescher, who called the 'nuclear' material because it was found in the nucleus. He then discovered that prokaryotic cells, which have no nuclei, also contain nucleic acids. The role of RNA in protein synthesis is thought to have been in 1939. Severo Ochoa won the 1959 Nobel Prize in Medicine (along with Arthur Kornberg) after he discovered an enzyme that could synthesize RNA in the laboratory. However, the enzyme discovered by Ochoa (polynucleotide phosphorylase) was later found to be responsible for RNA degradation, not RNA synthesis. In 1956 Alex Rich and David Davies combined two separate RNA strands to form the first crystals of RNA whose structure can be determined by X-ray crystallography.
The sequence of 77 nucleotides from tRNA yeast was discovered by Robert W. Holley in 1965, winning the Holley the 1968 Nobel Prize in Medicine (shared with Har Gobind Khorana and Marshall Nirenberg).
During the early 1970s, retroviruses and reverse transcriptases were discovered, showing for the first time that enzymes can copy RNA to DNA (as opposed to the usual route for transmitting genetic information). For this work, David Baltimore, Renato Dulbecco and Howard Temin were awarded the Nobel Prize in 1975. In 1976, Walter Fiers and his team determined the first complete nucleotide sequence of the RNA viral genome, the bacteriophage MS2.
In 1977, intricon and splicing RNA was found in both mammalian viruses and in cellular genes, earning a 1996 Nobel Laureate from Philip Sharp and Richard Roberts. Catalytic RNA molecules (ribozymes) were discovered in the early 1980s, leading to the 1989 Nobel Prize for Thomas Cech and Sidney Altman. In 1990, it was discovered at Petunia that the introduced gene could silence a similar gene from the plant itself, now known as a result of RNA interference.
At about the same time, 22 nt long RNA, now called microRNAs, was found to have a role in the development of C. elegans. Studies on RNA disorders obtained the Nobel Prize for Andrew Fire and Craig Mello in 2006, and another Nobel Prize was awarded for the study of RNA transcription to Roger Kornberg in the same year. The discovery of RNA gene regulation has led to efforts to develop drugs made from RNA, such as siRNA, to silence genes.
Relevance for prebiotic chemistry and abiogenesis
In 1967, Carl Woese hypothesized that RNA might be catalytic and suggested that the earliest life forms (self-replicating molecules) could rely on RNA to carry genetic information and catalyze the biochemical reactions of the RNA world.
In March 2015, complex DNA and RNA nucleotides, including uracil, cytosine and thymine, were reportedly formed in laboratories under space conditions, using starter chemicals, such as pyrimidine, an organic compound commonly found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), is one of the most carbon rich compounds found in the universe and may have formed in red giants or in dust and interstellar clouds.
See also
- origami RNA
- Biomolecular structure
- Macromolecule
- DNA
- RNA Biology History
- List of RNA Biologists
- Transcribe
References
External links
- RNA World website Linked links (structure, order, tools, journal)
- Nucleic Acid Database Images of DNA, RNA and complexes.
- Anna Marie Pyle Seminar: Structure of RNA, Function, and Recognition
Source of the article : Wikipedia
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