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Ribonucleic acid (RNA) is a
polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Repeat unit, repeating subunits. Due to thei ...

polymer
ic molecule essential in various biological roles in
coding Coding may refer to: Computer science * Computer programming, the process of creating and maintaining the source code of computer programs * Line coding, in data storage * Source coding, compression used in data transmission * Coding theory * Chann ...

coding
,
decoding
decoding
,
regulation Regulation is the management of complex systems A complex system is a system composed of many components which may interaction, interact with each other. Examples of complex systems are Earth's global climate, organisms, the human brain, infras ...
and
expression
expression
of
gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity..." (Greek language, Greek) meaning ''generation'' or ''birth'' ) is a basic unit of her ...

gene
s. RNA and deoxyribonucleic acid (
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
) are
nucleic acid Nucleic acids are biopolymer Biopolymers are natural polymers produced by the cells of Organism, living organisms. Biopolymers consist of monomeric units that are Covalent_bond, covalently bonded to form larger molecules. There are three main cla ...

nucleic acid
s. Along with
lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) dissolve in water, including s, es, s, fat-soluble s (such as vitamins A, ...
s,
protein Proteins are large s and s that comprise one or more long chains of . Proteins perform a vast array of functions within organisms, including , , , providing and , and from one location to another. Proteins differ from one another primarily ...

protein
s, and
carbohydrate is a disaccharide A disaccharide (also called a double sugar or ''biose'') is the sugar formed when two monosaccharides are joined by glycosidic linkage. Like monosaccharides, disaccharides are simple sugars soluble in water. Three common ex ...
s, nucleic acids constitute one of the four major
macromolecule macromolecule A macromolecule is a very large molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neu ...
s essential for all known forms of
life Life is a characteristic that distinguishes physical entities that have biological processes, such as Cell signaling, signaling and self-sustaining processes, from those that do not, either because such functions have ceased (they have Death ...

life
. Like DNA, RNA is assembled as a chain of
nucleotide Nucleotides are organic molecules , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...

nucleotide
s, but unlike DNA, RNA is found in nature as a single strand folded onto itself, rather than a paired double strand. Cellular organisms use
messenger RNA In molecular biology Molecular biology is the branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, molecular synthesis, modification, m ...
(''mRNA'') to convey genetic information (using the
nitrogenous bases File:Blausen 0324 DNA Pyrimidines.png, 230px, Pyrimidine nucleobases are simple ring molecules. Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides, which ...
of
guanine Guanine () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning ...

guanine
,
uracil Uracil () ( U or Ura) is one of the four s in the that are represented by the letters A, G, C and U. The others are (A), (C), and (G). In RNA, uracil binds to via two . In , the uracil nucleobase is replaced by . Uracil is a form of . Ura ...

uracil
,
adenine Adenine (A, Ade) is a nucleobase 230px, Pyrimidine nucleobases are simple ring molecules. Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleos ...

adenine
, and
cytosine Cytosine () (symbol A symbol is a mark, sign, or that indicates, signifies, or is understood as representing an , , or . Symbols allow people to go beyond what is n or seen by creating linkages between otherwise very different s and s. Al ...

cytosine
, denoted by the letters G, U, A, and C) that directs synthesis of specific proteins. Many
virus A virus is a that only inside the living of an . Viruses infect all , from animals and plants to s, including and . Since 's 1892 article describing a non-bacterial infecting tobacco plants and the discovery of the by in 1898, more ...

virus
es encode their genetic information using an RNA
genome In the fields of molecular biology and genetics, a genome is all genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The genome includes both the genes (the coding regions) and the noncodin ...

genome
. Some RNA molecules play an active role within cells by catalyzing biological reactions, controlling
gene expression Gene expression is the process by which information from a gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity..." (Greek language, ...

gene expression
, or sensing and communicating responses to cellular signals. One of these active processes is
protein synthesis Protein biosynthesis (or protein synthesis) is a core biological process, occurring inside cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small roo ...
, a universal function in which RNA molecules direct the synthesis of proteins on
ribosome Ribosomes ( ), also called Palade granules, are , found within all , that perform (mRNA translation). Ribosomes link together in the order specified by the s of (mRNA) molecules to form chains. Ribosomes consist of two major components: the ...

ribosome
s. This process uses
transfer RNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor composed of , typically 76 to 90 in length (in eukaryotes), that serves as the physical link between the and the sequence of proteins. Transfer RN ...
(''tRNA'') molecules to deliver
amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, c ...

amino acid
s to the ribosome, where
ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA A non-coding RNA (ncRNA) is an RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consis ...
(''rRNA'') then links amino acids together to form coded proteins.


Comparison with DNA

The chemical structure of RNA is very similar to that of
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
, but differs in three primary ways: * Unlike double-stranded DNA, RNA is a single-stranded molecule in many of its biological roles and consists of much shorter chains of nucleotides. However, a single RNA molecule can, by complementary base pairing, form intrastrand double helixes, as in tRNA. * While the sugar-phosphate "backbone" of DNA contains ''
deoxyribose Deoxyribose, or more precisely 2-deoxyribose, is a monosaccharide Monosaccharides (from Greek '' monos'': single, ''sacchar'': sugar), also called simple sugars, are the simplest form of sugar Sugar is the generic name for Sweetness, sweet ...

deoxyribose
'', RNA contains ''
ribose Ribose is a simple sugar and carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galactose and a molecule of D-glucose bonded by beta-1-4 glycosidic linkage. A carbohydrate () is a biomolecule consisting ...

ribose
'' instead. Ribose has a
hydroxyl A hydroxy or hydroxyl group is a functional group with the chemical formula -OH and composed of one oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the ...
group attached to the pentose ring in the 2' position, whereas deoxyribose does not. The hydroxyl groups in the ribose backbone make RNA more chemically
labile Lability refers to something that is constantly undergoing change or is likely to undergo change. Biochemistry In reference to biochemistry Biochemistry or biological chemistry, is the study of es within and relating to living s. A sub-d ...

labile
than DNA by lowering the
activation energy In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...

activation energy
of
hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution Substitution may refer to: Arts and media *Chord substitution, in music, swapping one chord for ...

hydrolysis
. * The complementary base to
adenine Adenine (A, Ade) is a nucleobase 230px, Pyrimidine nucleobases are simple ring molecules. Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleos ...

adenine
in DNA is
thymine Thymine () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning ...

thymine
, whereas in RNA, it is
uracil Uracil () ( U or Ura) is one of the four s in the that are represented by the letters A, G, C and U. The others are (A), (C), and (G). In RNA, uracil binds to via two . In , the uracil nucleobase is replaced by . Uracil is a form of . Ura ...

uracil
, which is an form of thymine.
Like DNA, most biologically active RNAs, including
mRNA upright=1.2, The "life cycle" of an mRNA in a eukaryotic cell. transcribed in the cell nucleus">nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central r ...

mRNA
,
tRNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an e ...

tRNA
,
rRNA Ribosomal ribonucleic acid (rRNA) is a type of which is the primary component of s, essential to all cells. rRNA is a which carries out in ribosomes. Ribosomal RNA is transcribed from (rDNA) and then bound to s to form and ribosome sub ...
,
snRNA Small nuclear RNA (snRNA) is a class of small RNA molecules that are found within the Cell nucleus#Splicing speckles, splicing speckles and Cajal body, Cajal bodies of the cell nucleus in eukaryotic cells. The length of an average snRNA is approxim ...
s, and other
non-coding RNA A non-coding RNA (ncRNA) is an RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecule File:Pentacene on Ni(111) STM.jpg, A s ...
s, contain self-complementary sequences that allow parts of the RNA to fold and pair with itself to form double helices. Analysis of these RNAs has revealed that they are highly structured. Unlike DNA, their structures do not consist of long double helices, but rather collections of short helices packed together into structures akin to proteins. In this fashion, RNAs can achieve chemical
catalysis Catalysis () is the process of increasing the of a by adding a substance known as a catalyst (). Catalysts are not consumed in the catalyzed reaction but can act repeatedly. Often only very small amounts of catalyst are required. The global ...

catalysis
(like enzymes). For instance, determination of the structure of the ribosome—an RNA-protein complex that catalyzes peptide bond formation—revealed that its active site is composed entirely of RNA.


Structure

Each
nucleotide Nucleotides are organic molecules , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...

nucleotide
in RNA contains a
ribose Ribose is a simple sugar and carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galactose and a molecule of D-glucose bonded by beta-1-4 glycosidic linkage. A carbohydrate () is a biomolecule consisting ...

ribose
sugar, with carbons numbered 1' through 5'. A base is attached to the 1' position, in general,
adenine Adenine (A, Ade) is a nucleobase 230px, Pyrimidine nucleobases are simple ring molecules. Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleos ...

adenine
(A),
cytosine Cytosine () (symbol A symbol is a mark, sign, or that indicates, signifies, or is understood as representing an , , or . Symbols allow people to go beyond what is n or seen by creating linkages between otherwise very different s and s. Al ...

cytosine
(C),
guanine Guanine () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning ...

guanine
(G), or
uracil Uracil () ( U or Ura) is one of the four s in the that are represented by the letters A, G, C and U. The others are (A), (C), and (G). In RNA, uracil binds to via two . In , the uracil nucleobase is replaced by . Uracil is a form of . Ura ...

uracil
(U). Adenine and guanine are
purine Purine is a heterocyclic 125px, Pyridine, a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s). Heterocyclic chemi ...

purine
s, cytosine and uracil are
pyrimidine Pyrimidine is an aromatic heterocyclic compound, heterocyclic organic compound similar to pyridine. One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has the nitrogen atoms at positions 1 and 3 in the ...

pyrimidine
s. A
phosphate In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo durin ...

phosphate
group is attached to the 3' position of one ribose and the 5' position of the next. The phosphate groups have a negative charge each, making RNA a charged molecule (polyanion). The bases form
hydrogen bond A hydrogen bond (or H-bond) is a primarily Electrostatics, electrostatic force of attraction between a hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of ...

hydrogen bond
s 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 binding to each other in a bulge, or the 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 A hydroxy or hydroxyl group is a functional group with the chemical formula -OH and composed of one oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the ...

hydroxyl
group at the 2' position of the . The presence of this functional group causes the helix to mostly take the A-form geometry, although in single strand dinucleotide contexts, RNA can rarely also adopt the B-form most commonly observed in DNA. The A-form geometry results in a very deep and narrow major groove and a shallow and wide minor groove. 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. RNA is transcribed with only four bases (adenine, cytosine, guanine and uracil), but these bases and attached sugars can be modified in numerous ways as the RNAs mature.
Pseudouridine Pseudouridine (abbreviated by the Greek letter psi- Ψ or the letter Q) is an isomer In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecule ...

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 (the most notable ones being in the TΨC loop of
tRNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an e ...

tRNA
). Another notable modified base is hypoxanthine, a deaminated adenine base whose
nucleoside Nucleosides are s that can be thought of as s without a . A nucleoside consists simply of a (also termed a nitrogenous base) and a five-carbon sugar ( or 2'-deoxyribose) whereas a nucleotide is composed of a nucleobase, a five-carbon sugar, and ...

nucleoside
is called
inosine Inosine is a nucleoside Nucleosides are glycosylamines that can be thought of as nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers deoxyribonucle ...

inosine
(I). Inosine plays a key role in the wobble hypothesis of the
genetic code The genetic code is the set of rules used by living to information encoded within genetic material ( or sequences of nucleotide triplets, or codons) into s. Translation is accomplished by the , which links s in an order specified by (mRNA), u ...

genetic code
. There are more than 100 other naturally occurring modified nucleosides. The greatest structural diversity of modifications can be found in
tRNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an e ...

tRNA
, while pseudouridine and nucleosides with 2'-O-methylribose often present in rRNA are the most common. 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. The functional form of single-stranded RNA molecules, just like proteins, frequently requires a specific
tertiary structure Biomolecular structure is the intricate folded, three-dimensional shape that is formed by a molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an elect ...
. The scaffold for this structure is provided by
secondary structural Biomolecular structure is the intricate folded, three-dimensional shape that is formed by a molecule of protein, DNA, or RNA, and that is important to its function. The structure of these molecules may be considered at any of several length scale ...

secondary structural
elements that are hydrogen bonds within the molecule. This leads to several recognizable "domains" of secondary structure like hairpin loops, bulges, and s. In order create, i.e., design, a RNA for any given secondary structure, two or three bases would not be enough, but four bases are enough. This is likely why nature has "chosen" a four base alphabet: less than four does not allow to create all structures, while more than four bases are not necessary. Since RNA is charged, metal ions such as are needed to stabilise many secondary and tertiary structures. The naturally occurring
enantiomer In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they und ...

enantiomer
of RNA is D-RNA composed of D-ribonucleotides. All chirality centers are located in the D-ribose. By the use of L-ribose or rather L-ribonucleotides, L-RNA can be synthesized. L-RNA is much more stable against degradation by
RNase Ribonuclease (commonly abbreviated RNase) is a type of nuclease A nuclease (also archaically known as nucleodepolymerase or polynucleotidase) is an enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts a ...
. Like other structured
biopolymers Biopolymers are natural polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacen ...
such as proteins, one can define topology of a folded RNA molecule. This is often done based on arrangement of intra-chain contacts within a folded RNA, termed as .


Synthesis

Synthesis of RNA is usually catalyzed by an enzyme—
RNA polymerase In molecular biology Molecular biology is the branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, molecular synthesis, modification, mec ...

RNA polymerase
—using DNA as a template, a process known as transcription. Initiation of transcription begins with the binding of the enzyme to a promoter sequence in the DNA (usually found "upstream" of a gene). The DNA double helix is unwound by the
helicase Helicases are a class of enzyme Enzymes () are s that act as s (biocatalysts). Catalysts accelerate . The molecules upon which enzymes may act are called , and the enzyme converts the substrates into different molecules known as . Almost ...

helicase
activity of the enzyme. 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.
Primary transcript A primary transcript is the single-stranded ribonucleic acid (RNA) product synthesized by Transcription (genetics), transcription of DNA, and processed to yield various mature RNA products such as mRNAs, tRNAs, and rRNAs. The primary transcripts ...
RNAs are often modified by enzymes after transcription. For example, a
poly(A) tail Polyadenylation is the addition of a poly(A) tail to an RNA transcript, typically a messenger RNA Image:MRNA-interaction.png, 500px, The "life cycle" of an mRNA in a eukaryote, eukaryotic cell. RNA is transcription (genetics), transcribed in the ...
and a
5' cap In molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molec ...
are added to eukaryotic
pre-mRNA Micrograph of gene transcription of ribosomal RNA illustrating the growing primary transcripts A primary transcript is the single-stranded ribonucleic acid (RNA) product synthesized by transcription of DNA, and processed to yield various mature ...

pre-mRNA
and
intron An intron (for ''intragenic region'') is any nucleotide sequence A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic molecul ...

intron
s are removed by the
spliceosome A spliceosome is a large ribonucleoprotein (RNP) complex found primarily within the nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom ...
. There are also a number of
RNA-dependent RNA polymerase RNA-dependent RNA polymerase (RdRP, RDR) or RNA replicase is an enzyme that catalyzes the self-replication, replication of RNA from an RNA template. Specifically, it catalyzes synthesis of the RNA strand Complementarity (molecular biology), comple ...
s that use RNA as their template for synthesis of a new strand of RNA. For instance, a number of
RNA viruses ''Orthornavirae'' is a kingdom of virus A virus is a submicroscopic infectious agent that Viral replication, replicates only inside the living Cell (biology), cells of an organism. Viruses infect all types of life forms, from animals and ...
(such as poliovirus) use this type of enzyme to replicate their genetic material. Also, RNA-dependent RNA polymerase is part of the
RNA interference RNA interference (RNAi) is a biological process in which RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting o ...
pathway in many organisms.


Types of RNA


Overview

Messenger RNA (mRNA) is the RNA that carries information from DNA to the
ribosome Ribosomes ( ), also called Palade granules, are , found within all , that perform (mRNA translation). Ribosomes link together in the order specified by the s of (mRNA) molecules to form chains. Ribosomes consist of two major components: the ...

ribosome
, the sites of protein synthesis (
translation Translation is the communication of the meaning Meaning most commonly refers to: * Meaning (linguistics), meaning which is communicated through the use of language * Meaning (philosophy), definition, elements, and types of meaning discusse ...

translation
) in the cell. The mRNA is a copy of DNA. The coding sequence of the mRNA determines the
amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, c ...

amino acid
sequence in the
protein Proteins are large s and s that comprise one or more long chains of . Proteins perform a vast array of functions within organisms, including , , , providing and , and from one location to another. Proteins differ from one another primarily ...

protein
that is produced. However, many RNAs do not code for protein (about 97% of the transcriptional output is non-protein-coding in eukaryotes). These so-called
non-coding RNA A non-coding RNA (ncRNA) is an RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecule File:Pentacene on Ni(111) STM.jpg, A s ...
s ("ncRNA") can be encoded by their own genes (RNA genes), but can also derive from mRNA
intron An intron (for ''intragenic region'') is any nucleotide sequence A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic molecul ...

intron
s. The most prominent examples of non-coding RNAs are
transfer RNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor composed of , typically 76 to 90 in length (in eukaryotes), that serves as the physical link between the and the sequence of proteins. Transfer RN ...
(tRNA) and
ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA A non-coding RNA (ncRNA) is an RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consis ...
(rRNA), both of which are involved in the process of translation. There are also non-coding RNAs involved in gene regulation,
RNA processing Post-transcriptional modification or co-transcriptional modification is a set of biological processes common to most eukaryotic cells by which an RNA primary transcript is chemically altered following transcription from a gene In biology, ...
and other roles. Certain RNAs are able to
catalyse Catalysis () is the process of increasing the rate of a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In cla ...

catalyse
chemical reactions such as cutting and other RNA molecules, and the catalysis of
peptide bond In organic chemistry, a peptide bond is an amide type of Covalent bond, covalent chemical bond linking two consecutive alpha-amino acids from C1 (carbon number one) of one alpha-amino acid and N2 (nitrogen number two) of another, along a peptide o ...

peptide bond
formation in the
ribosome Ribosomes ( ), also called Palade granules, are , found within all , that perform (mRNA translation). Ribosomes link together in the order specified by the s of (mRNA) molecules to form chains. Ribosomes consist of two major components: the ...

ribosome
; these are known as
ribozyme Ribozymes (ribonucleic acid enzymes) are RNA molecules that have the ability to catalyze specific biochemical reactions, including RNA splicing in gene expression, similar to the action of protein enzymes. The 1982 discovery of ribozymes demonst ...

ribozyme
s.


In length

According to the length of RNA chain, RNA includes
small RNA Small RNA are polymeric RNA molecules that are less than 200 nucleotides in length, and are usually non-coding RNA, non-coding. RNA silencing is often a function of these molecules, with the most common and well-studied example being RNA interferen ...
and long RNA. Usually,
small RNA Small RNA are polymeric RNA molecules that are less than 200 nucleotides in length, and are usually non-coding RNA, non-coding. RNA silencing is often a function of these molecules, with the most common and well-studied example being RNA interferen ...
s are shorter than 200  in length, and long RNAs are greater than 200  long. Long RNAs, also called large RNAs, mainly include
long non-coding RNA Long non-coding RNAs (long ncRNAs, lncRNA) are a type of RNA, generally defined as Transcription (genetics), transcripts more than 200 nucleotides that are not translated into protein. This arbitrary limit distinguishes long ncRNAs from small non ...
(lncRNA) and
mRNA upright=1.2, The "life cycle" of an mRNA in a eukaryotic cell. transcribed in the cell nucleus">nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central r ...

mRNA
. Small RNAs mainly include 5.8S
ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA A non-coding RNA (ncRNA) is an RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consis ...
(rRNA), 5S rRNA,
transfer RNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor composed of , typically 76 to 90 in length (in eukaryotes), that serves as the physical link between the and the sequence of proteins. Transfer RN ...
(tRNA),
microRNA A microRNA (abbreviated miRNA) is a small single-stranded non-coding RNA A non-coding RNA (ncRNA) is an RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or materi ...
(miRNA),
small interfering RNA Small interfering RNA (siRNA), sometimes known as short interfering RNA or silencing RNA, is a class of double-stranded RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance o ...
(siRNA),
small nucleolar RNA In molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mole ...
(snoRNAs),
Piwi-interacting RNA Piwi-interacting RNA (piRNA) is the largest class of small non-coding Non-coding DNA sequences are components of an organism's DNA that do not encode protein Proteins are large biomolecules or macromolecules that are comprised of one or more ...
(piRNA), tRNA-derived small RNA (tsRNA) and small rDNA-derived RNA (srRNA). There are certain exceptions as in the case of the 5S rRNA of the members of the genus Halococcus (
Archaea Archaea ( ; singular archaeon ) constitute a domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a pa ...

Archaea
), which have an insertion, thus increasing its size.


In translation

Messenger RNA In molecular biology Molecular biology is the branch of biology that seeks to understand the molecule, molecular basis of biological activity in and between Cell (biology), cells, including biomolecule, molecular synthesis, modification, m ...
(mRNA) carries information about a protein sequence to the
ribosome Ribosomes ( ), also called Palade granules, are , found within all , that perform (mRNA translation). Ribosomes link together in the order specified by the s of (mRNA) molecules to form chains. Ribosomes consist of two major components: the ...

ribosome
s, the protein synthesis factories in the cell. It is so that every three nucleotides (a
codon The genetic code is the set of rules used by living cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or reli ...

codon
) corresponds to one amino acid. In
eukaryotic Eukaryotes () are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...
cells, once precursor mRNA (pre-mRNA) has been transcribed from DNA, it is processed to mature mRNA. This removes its
intron An intron (for ''intragenic region'') is any nucleotide sequence A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic molecul ...

intron
s—non-coding sections of the pre-mRNA. The mRNA is then exported from the nucleus to the
cytoplasm In cell biology Cell biology (also cellular biology or cytology) is a branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
, where it is bound to ribosomes and
translated Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transla ...

translated
into its corresponding protein form with the help of
tRNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an e ...

tRNA
. 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
ribonuclease Ribonuclease (commonly abbreviated RNase) is a type of nuclease that catalyzes the degradation of RNA into smaller components. Ribonucleases can be divided into endoribonucleases and exoribonucleases, and comprise several sub-classes within t ...
s.
Transfer RNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an e ...
(tRNA) is a small RNA chain of about 80
nucleotide Nucleotides are organic molecules , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...

nucleotide
s that transfers a specific amino acid to a growing
polypeptide Peptides (from Greek language πεπτός, ''peptós'' "digested"; derived from πέσσειν, ''péssein'' "to digest") are short chains of amino acids linked by peptide bonds. Chains of fewer than ten or fifteen amino acids are called oligope ...
chain at the ribosomal site of protein synthesis during translation. It has sites for amino acid attachment and an
anticodon Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Le ...
region for
codon The genetic code is the set of rules used by living cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or reli ...

codon
recognition that binds to a specific sequence on the messenger RNA chain through hydrogen bonding.
Ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA A non-coding RNA (ncRNA) is an RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consis ...
(rRNA) is the catalytic component of the ribosomes. The rRNA is the component of the ribosome that hosts translation. Eukaryotic ribosomes contain four different rRNA molecules: 18S, 5.8S, 28S and 5S rRNA. Three of the rRNA molecules are synthesized in the
nucleolus The nucleolus (, plural: nucleoli ) is the largest structure in the nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nuc ...

nucleolus
, and one is synthesized elsewhere. 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. Nearly all the RNA found in a typical eukaryotic cell is rRNA. Transfer-messenger RNA (tmRNA) is found in many
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
and
plastid The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a membrane-bound organelle found in the cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spa ...
s. It tags proteins encoded by mRNAs that lack stop codons for degradation and prevents the ribosome from stalling.


Regulatory RNA

The earliest known regulators of
gene expression Gene expression is the process by which information from a gene In biology, a gene (from ''genos'' "...Wilhelm Johannsen coined the word gene to describe the Mendelian_inheritance#History, Mendelian units of heredity..." (Greek language, ...

gene expression
were proteins known as
repressor In molecular genetics, a repressor is a DNA-binding protein, DNA- or RNA-binding protein that inhibits the Gene expression, expression of one or more genes by binding to the Operator (biology), operator or associated Silencer (DNA), silencers. A ...
s and activators – regulators with specific short binding sites within enhancer regions near the genes to be regulated.  Later studies have shown that RNAs also regulate genes. There are several kinds of RNA-dependent processes in eukaryotes regulating the expression of genes at various points, such as
RNAi RNA interference (RNAi) is a biological process in which molecules are involved in sequence-specific suppression of gene expression by double-stranded RNA, through translational or transcriptional repression. Historically, RNAi was known by othe ...
repressing genes post-transcriptionally,
long non-coding RNA Long non-coding RNAs (long ncRNAs, lncRNA) are a type of RNA, generally defined as Transcription (genetics), transcripts more than 200 nucleotides that are not translated into protein. This arbitrary limit distinguishes long ncRNAs from small non ...
s shutting down blocks of
chromatin Chromatin is a complex of DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecu ...
epigenetically In biology, epigenetics is the study of heritable phenotype changes that do not involve alterations in the DNA sequence. The Ancient Greek, Greek prefix ''wikt:epi-, epi-'' ( "over, outside of, around") in ''epigenetics'' implies features that a ...
, and enhancer RNAs inducing increased gene expression. Prokaryote, Bacteria and archaea have also been shown to use regulatory RNA systems such as bacterial small RNAs and CRISPR. Fire and Mello were awarded the 2006 Nobel Prize in Physiology or Medicine for discovering
microRNA A microRNA (abbreviated miRNA) is a small single-stranded non-coding RNA A non-coding RNA (ncRNA) is an RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or materi ...
s (miRNAs), specific short RNA molecules that can base-pair with mRNAs."The Nobel Prize in Physiology or Medicine 2006". ''Nobelprize.org.'' Nobel Media AB 2014. Web. 6 Aug 2018. http://www.nobelprize.org/nobel_prizes/medicine/laureates/2006


RNA interference by miRNAs

Post-transcriptional expression levels of many genes can be controlled by
RNA interference RNA interference (RNAi) is a biological process in which RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting o ...
, in which miRNAs, specific short RNA molecules, pair with mRNA regions and target them for degradation. This Antisense RNA, antisense-based process involves steps that first process the RNA so that it can Base pair, base-pair with a region of its target mRNAs. Once the base pairing occurs, other proteins direct the mRNA to be destroyed by nucleases.


Long non-coding RNAs

Next to be linked to regulation were XIST, Xist and other long noncoding RNAs associated with X chromosome inactivation.  Their roles, at first mysterious, were shown by Jeannie T. Lee and others to be the RNA silencing, silencing of blocks of chromatin via recruitment of Polycomb-group proteins, Polycomb complex so that messenger RNA could not be transcribed from them. Additional lncRNAs, currently defined as RNAs of more than 200 base pairs that do not appear to have coding potential, have been found associated with regulation of stem cell pluripotency and cell division.


Enhancer RNAs

The third major group of regulatory RNAs is called enhancer RNAs.  It is not clear at present whether they are a unique category of RNAs of various lengths or constitute a distinct subset of lncRNAs.  In any case, they are transcribed from enhancers, which are known regulatory sites in the DNA near genes they regulate.  They up-regulate the transcription of the gene(s) under control of the enhancer from which they are transcribed.


Regulatory RNA in prokaryotes

At first, regulatory RNA was thought to be a eukaryotic phenomenon, a part of the explanation for why so much more transcription in higher organisms was seen than had been predicted. But as soon as researchers began to look for possible RNA regulators in bacteria, they turned up there as well, termed as small RNA (sRNA). Currently, the ubiquitous nature of systems of RNA regulation of genes has been discussed as support for the RNA World theory. Bacterial small RNAs generally act via Antisense RNA, antisense pairing with mRNA to down-regulate its translation, either by affecting stability or affecting cis-binding ability. Riboswitches have also been discovered. They are cis-acting regulatory RNA sequences acting Allosteric regulation, allosterically. They change shape when they bind metabolites so that they gain or lose the ability to bind chromatin to regulate expression of genes. Archaea also have systems of regulatory RNA. The CRISPR system, recently being used to edit DNA ''in situ'', acts via regulatory RNAs in archaea and bacteria to provide protection against virus invaders.


In RNA processing

Many RNAs are involved in modifying other RNAs. Introns are Splicing (genetics), spliced out of
pre-mRNA Micrograph of gene transcription of ribosomal RNA illustrating the growing primary transcripts A primary transcript is the single-stranded ribonucleic acid (RNA) product synthesized by transcription of DNA, and processed to yield various mature ...

pre-mRNA
by
spliceosome A spliceosome is a large ribonucleoprotein (RNP) complex found primarily within the nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom ...
s, which contain several small nuclear RNAs (snRNA), or the introns can be ribozymes that are spliced by themselves. RNA can also be altered by having its nucleotides modified to nucleotides other than adenosine, A, cytidine, C, guanosine, G and uridine, U. In eukaryotes, modifications of RNA nucleotides are in general directed by
small nucleolar RNA In molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, mole ...
s (snoRNA; 60–300 nt), found in the
nucleolus The nucleolus (, plural: nucleoli ) is the largest structure in the nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nuc ...

nucleolus
and Cajal body, cajal bodies. 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. RNA can also be methylated.


RNA genomes

Like DNA, RNA can carry genetic information. RNA viruses have
genome In the fields of molecular biology and genetics, a genome is all genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The genome includes both the genes (the coding regions) and the noncodin ...

genome
s composed of RNA that encodes a number of proteins. 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.


In reverse transcription

Reverse transcribing viruses replicate their genomes by Reverse transcription, reverse transcribing DNA copies from their RNA; these DNA copies are then transcribed to new RNA. Retrotransposons also spread by copying DNA and RNA from one another, and telomerase contains an RNA that is used as template for building the ends of Eukaryotic chromosome structure, eukaryotic chromosomes.


Double-stranded RNA

Double-stranded RNA (dsRNA) is RNA with two complementary strands, similar to the DNA found in all cells, but with the replacement of thymine by uracil and the adding of one oxygen atom. dsRNA forms the genetic material of some
virus A virus is a that only inside the living of an . Viruses infect all , from animals and plants to s, including and . Since 's 1892 article describing a non-bacterial infecting tobacco plants and the discovery of the by in 1898, more ...

virus
es (double-stranded RNA viruses). Double-stranded RNA, such as viral RNA or siRNA, can trigger
RNA interference RNA interference (RNAi) is a biological process in which RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting o ...
in eukaryotes, as well as interferon response in vertebrates.


Circular RNA

In the late 1970s, it was shown that there is a single stranded covalently closed, i.e. circular form of RNA expressed throughout the animal and plant kingdom (see Circular RNA, circRNA). circRNAs are thought to arise via a "back-splice" reaction where the
spliceosome A spliceosome is a large ribonucleoprotein (RNP) complex found primarily within the nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom ...
joins a downstream donor to an upstream acceptor splice site. So far the function of circRNAs is largely unknown, although for few examples a microRNA sponging activity has been demonstrated.


Key discoveries in RNA biology

Research on RNA has led to many important biological discoveries and numerous Nobel Prize, Nobel Prizes. Nucleic acids were discovered in 1868 by Friedrich Miescher, who called the material 'nuclein' since it was found in the Cell nucleus, nucleus. 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. Severo Ochoa won the 1959 Nobel Prize in Medicine (shared with Arthur Kornberg) after he discovered an enzyme that can synthesize RNA in the laboratory. However, the enzyme discovered by Ochoa (polynucleotide phosphorylase) was later shown to be responsible for RNA degradation, not RNA synthesis. In 1956 Alex Rich and David Davies hybridized two separate strands of RNA to form the first crystal of RNA whose structure could be determined by X-ray crystallography. The sequence of the 77 nucleotides of a yeast tRNA was found by Robert W. Holley in 1965, winning Holley the List of Nobel laureates in Physiology or Medicine, 1968 Nobel Prize in Medicine (shared with Har Gobind Khorana and Marshall Nirenberg). In the early 1970s, retroviruses and reverse transcriptase were discovered, showing for the first time that enzymes could copy RNA into DNA (the opposite of the usual route for transmission of genetic information). For this work, David Baltimore, Renato Dulbecco and Howard Temin were awarded a Nobel Prize in 1975. In 1976, Walter Fiers and his team determined the first complete nucleotide sequence of an RNA virus genome, that of bacteriophage MS2. In 1977,
intron An intron (for ''intragenic region'') is any nucleotide sequence A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides Nucleotides are organic molecul ...

intron
s and RNA splicing were discovered in both mammalian viruses and in cellular genes, resulting in a 1993 Nobel to Philip A. Sharp, Philip Sharp and Richard J. Roberts, Richard Roberts. Catalytic RNA molecules (
ribozyme Ribozymes (ribonucleic acid enzymes) are RNA molecules that have the ability to catalyze specific biochemical reactions, including RNA splicing in gene expression, similar to the action of protein enzymes. The 1982 discovery of ribozymes demonst ...

ribozyme
s) were discovered in the early 1980s, leading to a 1989 Nobel award to Thomas Cech and Sidney Altman. In 1990, it was found in ''Petunia'' that introduced genes can silence similar genes of the plant's own, now known to be a result of
RNA interference RNA interference (RNAi) is a biological process in which RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting o ...
. At about the same time, 22 nt long RNAs, now called
microRNA A microRNA (abbreviated miRNA) is a small single-stranded non-coding RNA A non-coding RNA (ncRNA) is an RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or materi ...
s, were found to have a role in the developmental biology, development of ''Caenorhabditis elegans, C. elegans''. Studies on RNA interference gleaned a Nobel Prize for Andrew Z. Fire, Andrew Fire and Craig Mello in 2006, and another Nobel was awarded for studies on the transcription of RNA to Roger Kornberg in the same year. The discovery of gene regulatory RNAs has led to attempts to develop drugs made of RNA, such as siRNA, to silence genes. Adding to the Nobel prizes awarded for research on RNA in 2009 it was awarded for the elucidation of the atomic structure of the ribosome to Venki Ramakrishnan, Tom Steitz, and Ada Yonath.


Relevance for prebiotic chemistry and abiogenesis

In 1968, Carl Woese hypothesized that RNA might be catalytic and suggested that the earliest forms of life (self-replicating molecules) could have relied on RNA both to carry genetic information and to catalyze biochemical reactions—an RNA world hypothesis, RNA world. In March 2015, complex
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
and RNA
nucleotide Nucleotides are organic molecules , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...

nucleotide
s, including
uracil Uracil () ( U or Ura) is one of the four s in the that are represented by the letters A, G, C and U. The others are (A), (C), and (G). In RNA, uracil binds to via two . In , the uracil nucleobase is replaced by . Uracil is a form of . Ura ...

uracil
,
cytosine Cytosine () (symbol A symbol is a mark, sign, or that indicates, signifies, or is understood as representing an , , or . Symbols allow people to go beyond what is n or seen by creating linkages between otherwise very different s and s. Al ...

cytosine
and
thymine Thymine () (symbol A symbol is a mark, sign, or word In linguistics, a word of a spoken language can be defined as the smallest sequence of phonemes that can be uttered in isolation with semantic, objective or pragmatics, practical meaning ...

thymine
, were reportedly formed in the laboratory under outer space conditions, using starter chemicals, such as
pyrimidine Pyrimidine is an aromatic heterocyclic compound, heterocyclic organic compound similar to pyridine. One of the three diazines (six-membered heterocyclics with two nitrogen atoms in the ring), it has the nitrogen atoms at positions 1 and 3 in the ...

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 been formed in red giants or in Cosmic dust, interstellar dust and gas clouds.


See also

* Biomolecular structure * RNA virus *
DNA Deoxyribonucleic acid (; DNA) is a molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically neutral gro ...

DNA
* History of RNA biology, History of RNA Biology * List of RNA biologists, List of RNA Biologists * RNA Society * Macromolecule * RNA-based evolution * RNA origami * Transcriptome * RNA world hypothesis


References


External links


RNA World website
Link collection (structures, sequences, tools, journals)
Nucleic Acid Database
Images of DNA, RNA and complexes.
Anna Marie Pyle's Seminar: RNA Structure, Function, and Recognition
{{DEFAULTSORT:Rna RNA, RNA splicing Molecular biology Biotechnology Nucleic acids