Citizendia

For other uses, see RNA (disambiguation).
A hairpin loop from a pre-mRNA. Notice its nitrogen-rich (blue) bases and oxygen-rich (red) backbone.
A hairpin loop from a pre-mRNA. Notice its nitrogen-rich (blue) bases and oxygen-rich (red) backbone.

Ribonucleic acid or RNA is a nucleic acid made from a long chain of nucleotide units. A nucleic acid is a Macromolecule composed of chains of monomeric Nucleotides In Biochemistry these Molecules carry Genetic information Nucleotides are Organic compounds that consist of three joined structures a nitrogenous base a Sugar, and a Phosphate group Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate. Structure The "skeleton" of adenine Ribose (ɹˈaɪbəʊs ɹˈaɪbəɹʊs primarily seen as D-ribose, is an Aldopentose — a Monosaccharide containing five Carbon A phosphate, an Inorganic chemical, is a salt of Phosphoric acid. RNA is very similar to DNA, but differs in a few important structural details: in the cell RNA is usually single stranded, while DNA is usually double stranded. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known RNA nucleotides contain ribose while DNA contains deoxyribose (a type of ribose that lacks one oxygen atom), and RNA has the nucleotide uracil rather than thymine which is present in DNA. Deoxyribose, also known as D-Deoxyribose and 2-deoxyribose, is an Aldopentose &mdash a Monosaccharide containing five Carbon Uracil is a common and naturally occurring Pyrimidine derivative Thymine is one of the four bases in the Nucleic acid of DNA that make up the letters ATGC

RNA is transcribed from DNA by enzymes called RNA polymerases and is generally further processed by other enzymes. Transcription is the synthesis of RNA under the direction of DNA Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins RNA polymerase ( RNAP or RNApol) is an Enzyme that produces RNA. Some of these RNA-processing enzymes contain RNA as part of their structures. RNA is also central to the translation of some RNAs into proteins. Translation is the first stage of Protein biosynthesis (part of the overall process of Gene expression) Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl In this process, a type of RNA called messenger RNA carries information from DNA to structures called ribosomes. Messenger ribonucleic acid ( mRNA) is a molecule of RNA encoding a chemical "blueprint" for a Protein product Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that These ribosomes are made from proteins and ribosomal RNAs, which come together to form a molecular machine that can read messenger RNAs and translate the information they carry into proteins. It has also been known since the 1990s that several types of RNA regulate which genes are active. Gene modulation redirects here For information on therapeutic regulation of gene expression see Therapeutic gene modulation.

Contents

Structure

Watson-Crick base pairs in a siRNA (hydrogen atoms are not shown)
Watson-Crick base pairs in a siRNA (hydrogen atoms are not shown)

Each nucleotide in RNA contains a ribose sugar, with carbons numbered 1' through 5'. Small interfering RNA ( siRNA) sometimes known as short interfering RNA or silencing RNA, is a class of 20-25 Nucleotide -long double-stranded A base is attached to the 1' position, generally adenine (A), cytosine (C), guanine (G) or uracil (U). Adenine is a Purine with a variety of roles in Biochemistry including Cellular respiration, in the form of both the energy-rich Adenosine Cytosine is one of the five main bases found in DNA and RNA. It is a Pyrimidine derivative with a Heterocyclic Aromatic ring Guanine is one of the five main Nucleobases found in the Nucleic acids DNA and RNA, the others being Adenine, Cytosine, Uracil is a common and naturally occurring Pyrimidine derivative Adenine and guanine are purines, cytosine and uracil are pyrimidines. Purine ( 1) is a heterocyclic Aromatic Organic compound, consisting of a Pyrimidine ring fused to an Imidazole ring Pyrimidine is a Heterocyclic Aromatic Organic compound similar to Benzene and Pyridine, containing two Nitrogen Atoms A phosphate group is attached to the 3' position of one ribose and the 5' position of the next. A phosphate, an Inorganic chemical, is a salt of Phosphoric acid. The phosphate groups have a negative charge each at physiological pH, making RNA a charged molecule (polyanion). The bases may form hydrogen bonds between cytosine and guanine, between adenine and uracil and between guanine and uracil. A hydrogen bond results from a Dipole-dipole force between an Electronegative atom and a Hydrogen atom bonded to Nitrogen, Oxygen [1] However other interactions are possible, such as a group of adenine bases binding to each other in a bulge,[2] or the GNRA tetraloop that has a guanine–adenine base-pair. Tetraloops are a type of four-base Hairpin loop motifs in RNA secondary structure that cap many double helices [1]

Chemical structure of RNA
Chemical structure of RNA

An important structural feature of RNA that distinguishes it from DNA is the presence of a hydroxyl group at the 2' position of the ribose sugar. Hydroxyl in Chemistry stands for a molecule consisting of an Oxygen atom and a Hydrogen atom connected by a Covalent bond. The presence of this functional group causes the helix to adopt the A-form geometry rather than the B-form most commonly observed in DNA. A-DNA is one of the many possible double helical structures of DNA. [3] This results in a very deep and narrow major groove and a shallow and wide minor groove. [4] A second consequence of the presence of the 2'-hydroxyl group is that in conformationally flexible regions of an RNA molecule (that is, not involved in formation of a double helix), it can chemically attack the adjacent phosphodiester bond to cleave the backbone. [5]

RNA is transcribed with only four bases (adenine, cytosine, guanine and uracil),[6] but there are numerous modified bases and sugars in mature RNAs. Pseudouridine (Ψ), in which the linkage between uracil and ribose is changed from a C–N bond to a C–C bond, and ribothymidine (T), are found in various places (most notably in the TΨC loop of tRNA). Pseudouridine (abbreviated Ψ is the C-glycoside Isomer of the Nucleoside Uridine, and it is the most prevalent of the over one hundred different modified Transfer RNA (abbreviated tRNA) is a small RNA (usually about 74-95 nucleotides that transfers a specific Amino acid to a growing polypeptide chain at [7] Another notable modified base is hypoxanthine, a deaminated adenine base whose nucleoside is called inosine. See also Adenosine triphosphate (ATP Inosine is a Nucleoside that is formed when Hypoxanthine is attached to a Ribose ring (also known as a Ribofuranose) via a β-N9- Inosine plays a key role in the wobble hypothesis of the genetic code. The genetic code is the set of rules by which information encoded in genetic material ( DNA or RNA sequences is translated into Proteins [8] There are nearly 100 other naturally occurring modified nucleosides,[9] of which pseudouridine and nucleosides with 2'-O-methylribose are the most common. 2'- O -methylation is a common Nucleoside modification of RNA, where a Methyl group is added to the 2' hydroxyl group of the Ribose [10] The specific roles of many of these modifications in RNA are not fully understood. However, it is notable that in ribosomal RNA, many of the post-transcriptional modifications occur in highly functional regions, such as the peptidyl transferase center and the subunit interface, implying that they are important for normal function. [11]

Secondary structure of a telomerase RNA
Secondary structure of a telomerase RNA

The functional form of single stranded RNA molecules, just like proteins, frequently requires a specific tertiary structure. Telomerase is a Ribonucleoprotein Reverse transcriptase that synthesises telomeric DNA The scaffold for this structure is provided by secondary structural elements which are hydrogen bonds within the molecule. This leads to several recognizable "domains" of secondary structure like hairpin loops, bulges and internal loops. Stem-loop intramolecular Base pairing is a pattern that can occur in single-stranded DNA or more commonly in RNA. [12] There has been a significant amount of research directed at RNA structure prediction. The functional form of single stranded RNA molecules frequently requires a specific tertiary structure

Comparison with DNA

RNA and DNA differ in three main ways. Deoxyribonucleic acid ( DNA) is a Nucleic acid that contains the genetic instructions used in the development and functioning of all known First, unlike DNA which is double-stranded, RNA is a single-stranded molecule in most of its biological roles and has a much shorter chain of nucleotides. Second, while DNA contains deoxyribose, RNA contains ribose, (there is no hydroxyl group attached to the pentose ring in the 2' position in DNA). Molecular biologists use several shorthand terms when referring to Nucleic acid molecules such as DNA and RNA, collectively referred to as nucleic These hydroxyl groups make RNA less stable than DNA because it is more prone to hydrolysis. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions Third, the complementary nucleotide to adenine is not thymine, as it is in DNA, but rather uracil, which is an unmethylated form of thymine. Adenine is a Purine with a variety of roles in Biochemistry including Cellular respiration, in the form of both the energy-rich Adenosine Thymine is one of the four bases in the Nucleic acid of DNA that make up the letters ATGC Uracil is a common and naturally occurring Pyrimidine derivative Methylation is a term used in the chemical sciences to denote the attachment or substitution of a methyl group on various substrates. [13]

The 50S ribosomal subunit. RNA is in orange, protein in blue. The active site is in the middle (red).
The 50S ribosomal subunit. Note Sometimes the ' 50s is used as shorthand for the 1950s, the 1850s, or other such decades in various centuries Events and Trends RNA is in orange, protein in blue. The active site is in the middle (red).

Like DNA, most biologically active RNAs including tRNA, rRNA, snRNAs and other, non-coding, RNAs are extensively base paired to form double stranded helices. Structural analysis of these RNAs have revealed that they are highly structured. Unlike DNA, this structure is not long double-stranded helices but rather collections of short helices packed together into structures akin to proteins. In this fashion, RNAs can achieve chemical catalysis, like enzymes. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst [14] For instance, determination of the structure of the ribosome—an enzyme that catalyzes peptide bond formation—revealed that its active site is composed entirely of RNA. [15]

Synthesis

Synthesis of RNA is usually catalyzed by an enzyme—RNA polymerase—using DNA as a template, a process known as transcription. RNA polymerase ( RNAP or RNApol) is an Enzyme that produces RNA. Transcription is the synthesis of RNA under the direction of DNA Initiation of transcription begins with the binding of the enzyme to a promoter sequence in the DNA (usually found "upstream" of a gene). In Biology, a promoter is a region of DNA that facilitates the transcription of a particular Gene. The DNA double helix is unwound by the helicase activity of the enzyme. Helicases are a class of Enzymes vital to all living Organisms They are motor proteins that move directionally along a Nucleic acid phosphodiester backbone The enzyme then progresses along the template strand in the 3’ to 5’ direction, synthesizing a complementary RNA molecule with elongation occurring in the 5’ to 3’ direction. The DNA sequence also dictates where termination of RNA synthesis will occur. [16]

RNAs are often modified by enzymes after transcription. Post-transcriptional modification is a process in Cell biology by which in Eukaryotic cells, primary transcript RNA is converted into mature For example, a poly(A) tail and a 5' cap are added to eukaryotic pre-mRNA. Polyadenylation is the synthesis of a poly(A tail a stretch of RNA where all the bases are Adenines at the end of an RNA molecule The 5' cap is a specially altered Nucleotide end to the 5' end of Precursor messenger RNA and some other primary RNA transcripts as found in Eukaryotes Precursor mRNA ( pre-mRNA) also termed heterogeneous nuclear RNA ( hnRNA) is an immature single strand of messenger ribonucleic acid ( MRNA

There are also a number of RNA-dependent RNA polymerases as well that use RNA as their template for synthesis of a new strand of RNA. RNA-dependent RNA polymerase ( RDRP) or RNA replicase, is an Enzyme that catalyzes the replication of RNA from an RNA template For instance, a number of RNA viruses (such as poliovirus) use this type of enzyme to replicate their genetic material. [17] Also, it is known that RNA-dependent RNA polymerases are required for the RNA interference pathway in many organisms. RNA interference ( RNAi) is a mechanism that inhibits Gene expression at the stage of translation or by hindering the transcription of specific [18]

Types of RNA

See also: List of RNAs

Overview

Structure of a hammerhead ribozyme, a ribozyme that cuts RNA
Structure of a hammerhead ribozyme, a ribozyme that cuts RNA

Messenger RNA (mRNA) is the RNA that carries information from DNA to the ribosome, the sites of protein synthesis (translation) in the cell. This is a list of RNAs in nature Some of these categories are broad others are single RNA families Hammerhead RNAs are small self-cleaving RNAs that have a conserved motif found in several of the Viroids and satellite RNAs associated with plant RNA Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that Translation is the first stage of Protein biosynthesis (part of the overall process of Gene expression) The coding sequence of the mRNA determines the amino acid sequence in the protein that is produced. In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl [19] Many RNAs do not code for protein however. These non-coding RNAs can be encoded by their own genes (RNA genes), but can also derive from mRNA introns. A non-coding RNA ( ncRNA) is any RNA molecule that is not translated into a Protein. Introns, derived from the term "intragenic regions" and also called intervening sequence (IVS are DNA regions in a Gene that are not translated into [20] The most prominent examples of non-coding RNAs are transfer RNA (tRNA) and ribosomal RNA (rRNA), both of which are involved in the process of translation. Transfer RNA (abbreviated tRNA) is a small RNA (usually about 74-95 nucleotides that transfers a specific Amino acid to a growing polypeptide chain at Ribosomal RNA ( rRNA) is the central component of the Ribosome, the protein manufacturing machinery of all living cells. [13] There are also non-coding RNAs involved in gene regulation, RNA processing and other roles. Post-transcriptional modification is a process in Cell biology by which in Eukaryotic cells, primary transcript RNA is converted into mature Certain RNAs are able to catalyse chemical reactions such as cutting and ligating other RNA molecules,[21] and the catalysis of peptide bond formation in the ribosome;[15] these are known as ribozymes. Catalysis is the process in which the rate of a Chemical reaction is increased by means of a Chemical substance known as a catalyst In Biochemistry, a ligase (from the Latin verb ligāre &mdash "to bind" or "to glue together" is an Enzyme that can catalyse A peptide bond is a Chemical bond formed between two Molecules when the Carboxyl group of one molecule reacts with the Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that A ribozyme (from ribo nucleic acid en' zyme', also called RNA Enzyme or catalytic RNA is an RNA Molecule that catalyzes

In translation

Messenger RNA (mRNA) carries information about a protein sequence to the ribosomes, the protein synthesis factories in the cell. Messenger ribonucleic acid ( mRNA) is a molecule of RNA encoding a chemical "blueprint" for a Protein product Ribosomes ( from ribo nucleic acid and "Greek soma ( meaning body") are complexes of RNA and Protein that It is coded so that every three nucleotides (a codon) correspond to one amino acid. The genetic code is the set of rules by which information encoded in genetic material ( DNA or RNA sequences is translated into Proteins In eukaryotic cells, once precursor mRNA (pre-mRNA) has been transcribed from DNA, it is processed to mature mRNA. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex This removes its introns—non-coding sections of the pre-mRNA. Introns, derived from the term "intragenic regions" and also called intervening sequence (IVS are DNA regions in a Gene that are not translated into The mRNA is then exported from the nucleus to the cytoplasm, where it is bound to ribosomes and translated into its corresponding protein form with the help of tRNA. Translation is the first stage of Protein biosynthesis (part of the overall process of Gene expression) Transfer RNA (abbreviated tRNA) is a small RNA (usually about 74-95 nucleotides that transfers a specific Amino acid to a growing polypeptide chain at In prokaryotic cells, which do not have nucleus and cytoplasm compartments, mRNA can bind to ribosomes while it is being transcribed from DNA. After a certain amount of time the message degrades into its component nucleotides with the assistance of ribonucleases. Ribonuclease, abbreviated commonly as RNase, is a Nuclease that catalyzes the degradation of RNA into smaller components [19]

Transfer RNA (tRNA) is a small RNA chain of about 80 nucleotides that transfers a specific amino acid to a growing polypeptide chain at the ribosomal site of protein synthesis during translation. Transfer RNA (abbreviated tRNA) is a small RNA (usually about 74-95 nucleotides that transfers a specific Amino acid to a growing polypeptide chain at Nucleotides are Organic compounds that consist of three joined structures a nitrogenous base a Sugar, and a Phosphate group Peptides (from the Greek πεπτίδια, "small digestibles" are short Polymers formed from the linking in a defined order of α- Amino It has sites for amino acid attachment and an anticodon region for codon recognition that binds to a specific sequence on the messenger RNA chain through hydrogen bonding. Transfer RNA (abbreviated tRNA) is a small RNA (usually about 74-95 nucleotides that transfers a specific Amino acid to a growing polypeptide chain at The genetic code is the set of rules by which information encoded in genetic material ( DNA or RNA sequences is translated into Proteins [20]

Ribosomal RNA (rRNA) is the catalytic component of the ribosomes. Ribosomal RNA ( rRNA) is the central component of the Ribosome, the protein manufacturing machinery of all living cells. Eukaryotic ribosomes contain four different rRNA molecules: 18S, 5. 8S, 28S and 5S rRNA. Three of the rRNA molecules are synthesized in the nucleolus, and one is synthesized elsewhere. The nucleolus (also called nucleole) is a structure found within the nucleus in which Ribosomal RNA is transcribed. In the cytoplasm, ribosomal RNA and protein combine to form a nucleoprotein called a ribosome. The ribosome binds mRNA and carries out protein synthesis. Several ribosomes may be attached to a single mRNA at any time. [19] rRNA is extremely abundant and makes up 80% of the 10 mg/ml RNA found in a typical eukaryotic cytoplasm. The cytoplasm is the contents of a cell that is enclosed within the Plasma membrane. [22]

Transfer-messenger RNA (tmRNA) is found in many bacteria and plastids. tmRNA (also known as 10Sa RNA) stands for transfer-messenger-RNA The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have Plastids are major Organelles found in plants and algae Plastids often contain pigments used in photosynthesis and the types of pigments present can change It tags proteins encoded by mRNAs that lack stop codons for degradation and prevents the ribosome from stalling. [23]

In gene regulation

Several types of RNA can downregulate gene expression by being complementary to a part of an mRNA or gene. MicroRNAs (miRNA; 21-22 nt) are found in eukaryotes and act through RNA interference (RNAi), where an effector complex of miRNA and enzymes can break down mRNA which the miRNA is complementary to, block the mRNA from being translated, or cause a promoter to be methylated which generally downregulates its gene. In Genetics, microRNAs ( miRNA) are single-stranded RNA molecules of about 21–23 Nucleotides in length which regulate Gene expression Nucleotides are Organic compounds that consist of three joined structures a nitrogenous base a Sugar, and a Phosphate group RNA interference ( RNAi) is a mechanism that inhibits Gene expression at the stage of translation or by hindering the transcription of specific In Biology, a promoter is a region of DNA that facilitates the transcription of a particular Gene. [24] Some miRNAs upregulate genes instead (RNA activation). Small double-stranded RNA (dsRNA has been found to silence gene expression by an evolutionally conserved mechanism known as RNA interference or RNAi. [25] While small interfering RNAs (siRNA; 20-25 nt) are often produced by breakdown of viral RNA, there are also endogenous sources of siRNAs in plants. Small interfering RNA ( siRNA) sometimes known as short interfering RNA or silencing RNA, is a class of 20-25 Nucleotide -long double-stranded [26] siRNAs act through RNA interference in a fashion similar to miRNAs, including RNA activation. [27] Animals have Piwi-interacting RNAs (piRNA; 29-30 nt) which are active in germline cells and are thought to be a defense against transposons and play a role in gametogenesis. Piwi-interacting RNA ( piRNA) is a class of small RNA molecules that is expressed in Mammalian Testes and somatic cells and forms RNA-protein complexes In Biology and Genetics, the germline of a mature or developing individual is the line (sequence of Germ cells that have genetic material that Transposons are sequences of DNA that can move around to different positions within the Genome of a single cell, a process called transposition Gametogenesis is a process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid Gametes Depending on the Biological [28][29] Antisense RNAs are widespread among bacteria; most downregulate a gene, but a few are activators of transcription. Antisense RNA ( aRNA) is single-stranded RNA that is complementary to a Messenger RNA (mRNA strand transcribed within a cell [30] Antisense RNA acts by binding to an mRNA, forming double-stranded RNA that is degraded by enzymes. [31] There are many mRNA-like large non-coding RNAs that regulate genes in eukaryotes,[32] one such RNA is Xist which coats one X chromosome in female mammals and inactivates it. Xist is an RNA gene on the X chromosome of the placental mammals that acts as major effector of the X inactivation process X-inactivation (also called lyonization) is a process by which one of the two copies of the X chromosome present in Female Mammals is inactivated [33]

An mRNA may contain regulatory elements itself, such as riboswitches, in the 5' UTR or 3' UTR; these cis-regulatory elements regulate the activity of that mRNA. In Molecular biology, a riboswitch is a part of an MRNA molecule that can directly bind a small target molecule, and whose binding of the target affects The five prime untranslated region ( 5' UTR) also known as the leader sequence, is a particular section of Messenger RNA (mRNA and the DNA that codes for The three prime untranslated region (3' UTR is a particular section of Messenger RNA (mRNA A cis-regulatory element or cis-element is a region of DNA or RNA that regulates the expression of Genes located on that same strand [34]

In RNA processing

Uridine to pseudouridine is a common RNA modification.
Uridine to pseudouridine is a common RNA modification.

Many RNAs are involved in modifying other RNAs. Introns are spliced out of pre-mRNA by spliceosomes, which contain several small nuclear RNAs (snRNA),[13] or the introns can be ribozymes that are spliced by themselves. Introns, derived from the term "intragenic regions" and also called intervening sequence (IVS are DNA regions in a Gene that are not translated into In Molecular biology, splicing is a modification of an RNA after transcription, in which Introns are removed and Exons are joined Precursor mRNA ( pre-mRNA) also termed heterogeneous nuclear RNA ( hnRNA) is an immature single strand of messenger ribonucleic acid ( MRNA A spliceosome is a complex of specialized RNA and Protein subunits that removes Introns from a transcribed pre- mRNA ( HnRNA Small nuclear RNA (snRNA is a class of small RNA molecules that are found within the nucleus of eukaryotic cells [35] RNA can also be altered by having its nucleotides modified to other nucleotides than A, C, G and U. Adenosine is a Nucleoside composed of a Molecule of Adenine attached to a Ribose sugar molecule ( Ribofuranose) moiety via a β-N9- Cytidine is a Nucleoside Molecule that is formed when Cytosine is attached to a Ribose ring (also known as a Ribofuranose) via Guanosine is a Nucleoside comprising Guanine attached to a Ribose ( Ribofuranose) ring via a β-N9- Glycosidic bond. Uridine is a molecule (known as a Nucleoside) that is formed when Uracil is attached to a Ribose ring (also known as a Ribofuranose) via a β-N1- In eukaryotes, modifications of RNA nucleotides are generally directed by small nucleolar RNAs (snoRNA; 60-300 nt),[20] found in the nucleolus and cajal bodies. Small nucleolar RNAs (snoRNAs are a class of small RNA molecules that guide chemical modifications ( Methylation or pseudouridylation of Ribosomal RNAs The nucleolus (also called nucleole) is a structure found within the nucleus in which Ribosomal RNA is transcribed. Cajal bodies (CBs are spherical sub-organelles found in the nucleus of proliferative cells like Tumor cells or metabolically active cells like Neurons snoRNAs associate with enzymes and guide them to a spot on an RNA by basepairing to that RNA. These enzymes then perform the nucleotide modification. rRNAs and tRNAs are extensively modified, but snRNAs and mRNAs can also be the target of base modification. [36][37]

RNA genomes

Like DNA, RNA can be an information carrier. RNA viruses have genomes composed of RNA, plus a variety of proteins encoded by that genome. An RNA virus is a Virus that has RNA (ribonucleic acid as its Genetic material. In classical genetics the genome of a Diploid Organism including Eukarya refers to a full set of chromosomes or genes in a Gamete, thereby The viral genome is replicated by some of those proteins, while other proteins protect the genome as the virus particle moves to a new host cell. Viroids are another group of pathogens, but they consist only of RNA, do not encode any protein and are replicated by a host plant cell's polymerase. Viroids are Plant Pathogens that consist of a short stretch (a few hundred nucleobases) of highly complementary circular single-stranded [38]

In reverse transcription

Reverse transcribing viruses replicate their genomes by reverse transcribing DNA copies from their RNA; these DNA copies are then transcribed to new RNA. A reverse transcribing virus is any virus which replicates using Reverse transcription, the formation of DNA from an RNA template Reverse transcription is the process of making a double stranded DNA (deoxyribonucleic acid molecule from a single stranded RNA (ribonucleic acid template Retrotransposons also spread by copying DNA and RNA from one another,[39] and telomerase contains an RNA that is used as template for building the ends of eukaryotic chromosomes. Retrotransposons (also called transposons via RNA intermediates are genetic elements that can amplify themselves in a Genome and are ubiquitous components of the Telomerase is an Enzyme that adds specific DNA sequence repeats ("TTAGGG" in all vertebrates to the 3' ("three prime" end of DNA strands in the [40]

Double-stranded RNA

Double-stranded RNA (dsRNA) is RNA with two complementary strands, similar to the DNA found in all cells. dsRNA forms the genetic material of some viruses (double-stranded RNA viruses). A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable Double-stranded ( ds) RNA viruses are a diverse group of Viruses that vary widely in host range (humans animals plants Fungi, and Double-stranded RNA such as viral RNA or siRNA can trigger RNA interference in eukaryotes, as well as interferon response in vertebrates. Small interfering RNA ( siRNA) sometimes known as short interfering RNA or silencing RNA, is a class of 20-25 Nucleotide -long double-stranded RNA interference ( RNAi) is a mechanism that inhibits Gene expression at the stage of translation or by hindering the transcription of specific Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Interferons ( IFN s are natural Proteins produced by the cells of the Immune system of most Vertebrates in response to challenges by foreign agents Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes [41][42][43]

Discovery

Nucleic acids were discovered in 1868 by Friedrich Miescher, who called the material 'nuclein' since it was found in the nucleus. A nucleic acid is a Macromolecule composed of chains of monomeric Nucleotides In Biochemistry these Molecules carry Genetic information Johannes Friedrich Miescher ( 13 August 1844, Basel - 26 August 1895, Davos) was a Swiss Biologist In Cell biology, the nucleus (pl nuclei; from Latin la ''nucleus'' or la ''nuculeus'' "little nut" or kernel is a membrane-enclosed [44] It was later discovered that prokaryotic cells, which do not have a nucleus, also contain nucleic acids. The role of RNA in protein synthesis was suspected already in 1939. [45] Severo Ochoa won the 1959 Nobel Prize in Medicine after he discovered how RNA is synthesized. Severo Ochoa de Albornoz ( September 24, 1905 &ndash November 1, 1993) was a Spanish - American biochemist The Nobel Prize in Physiology or Medicine (Nobelpriset i fysiologi eller medicin is awarded once a year by the Swedish Karolinska Institute. [46] The sequence of the 77 nucleotides of a yeast tRNA was found by Robert W. Holley in 1965,[47] winning Holley the 1968 Nobel Prize in Medicine. Robert William Holley ( January 28, 1922 &ndash February 11, 1993) was an American Biochemist, he was awarded the Nobel Prize Carl Woese realised RNA can be catalytic in 1967 and proposed that the earliest forms of life relied on RNA both to carry genetic information and to catalyze biochemical reactions—an RNA world. Carl Richard Woese (born July 15 1928, Syracuse New York) is an American Microbiologist who attended Deerfield Academy The RNA world hypothesis proposes that a world filled with life based on Ribonucleic acid (RNA predated current life based on Deoxyribonucleic acid (DNA [48][49] In 1976, Walter Fiers and his team determined the first complete nucleotide sequence of an RNA virus genome, that of bacteriophage MS2. Walter Fiers (b Ieper, Belgium, 1931 is a Belgian molecular biologist The bacteriophage MS2. MS2 phage is an icosahedral bacteriophage with a diameter of 27-34nm and an isoelectric point (pI of 3 [50] In 1990 it was found that introduced genes can silence homologous endogenous genes in plants,[51] now known to be a result of RNA interference. RNA interference ( RNAi) is a mechanism that inhibits Gene expression at the stage of translation or by hindering the transcription of specific [52] At about the same time, 22 nt long RNAs, now called microRNAs, were found to have a role in the development of C. elegans. In Genetics, microRNAs ( miRNA) are single-stranded RNA molecules of about 21–23 Nucleotides in length which regulate Gene expression Developmental Biology is the official journal of the Society for Developmental Biology. Caenorhabditis elegans (ˌsiːnoʊræbˈdaɪtɪs ˈɛlɪgænz is a free-living Nematode (roundworm about 1  mm in length which [53] The discovery of gene regulatory RNAs has led to attempts to develop drugs made of RNA, like siRNA, to silence genes. Small interfering RNA ( siRNA) sometimes known as short interfering RNA or silencing RNA, is a class of 20-25 Nucleotide -long double-stranded [54]

See also

References

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