134-407: Ribonucleic acid ( RNA ) is a polymeric molecule that is essential for most biological functions, either by performing the function itself ( non-coding RNA ) or by forming a template for the production of proteins ( messenger RNA ). RNA and deoxyribonucleic acid (DNA) are nucleic acids . The nucleic acids constitute one of the four major macromolecules essential for all known forms of life . RNA
268-459: A catalyst . Laboratory synthesis of biopolymers, especially of proteins , is an area of intensive research. There are three main classes of biopolymers: polysaccharides , polypeptides , and polynucleotides . In living cells, they may be synthesized by enzyme-mediated processes, such as the formation of DNA catalyzed by DNA polymerase . The synthesis of proteins involves multiple enzyme-mediated processes to transcribe genetic information from
402-668: A hydrogen atom in place of the hydroxyl group at C2'. This hydroxyl group performs a function in RNA splicing . The " d -" in the name d -ribose refers to the stereochemistry of the chiral carbon atom farthest away from the aldehyde group (C4'). In d -ribose, as in all d -sugars, this carbon atom has the same configuration as in d -glyceraldehyde . Relative abundance of forms of ribose in solution: β- d -ribopyranose (59%), α- d -ribopyranose (20%), β- d -ribofuranose (13%), α- d -ribofuranose (7%) and open chain (0.1%). For ribose residues in nucleosides and nucleotide ,
536-441: A lower critical solution temperature phase transition (LCST), at which phase separation occurs with heating. In dilute solutions, the properties of the polymer are characterized by the interaction between the solvent and the polymer. In a good solvent, the polymer appears swollen and occupies a large volume. In this scenario, intermolecular forces between the solvent and monomer subunits dominate over intramolecular interactions. In
670-432: A structural analog , deoxyribose , which is a similarly essential component of DNA . l -ribose is an unnatural sugar that was first prepared by Emil Fischer and Oscar Piloty in 1891. It was not until 1909 that Phoebus Levene and Walter Jacobs recognised that d -ribose was a natural product , the enantiomer of Fischer and Piloty's product, and an essential component of nucleic acids . Fischer chose
804-482: A 1993 Nobel to Philip Sharp and Richard Roberts . Catalytic RNA molecules ( ribozymes ) 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 . At about the same time, 22 nt long RNAs, now called microRNAs , were found to have
938-498: A bad solvent or poor solvent, intramolecular forces dominate and the chain contracts. In the theta solvent , or the state of the polymer solution where the value of the second virial coefficient becomes 0, the intermolecular polymer-solvent repulsion balances exactly the intramolecular monomer-monomer attraction. Under the theta condition (also called the Flory condition), the polymer behaves like an ideal random coil . The transition between
1072-424: A certain amount of time, the message degrades into its component nucleotides with the assistance of ribonucleases . 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. It has sites for amino acid attachment and an anticodon region for codon recognition that binds to
1206-531: A change in the cell depending on the original signal molecule. The opposite occurs when an inhibitory G-protein is activated; the G-protein inhibits adenylyl cyclase and ATP is not converted to cAMP. Ribose is referred to as the "molecular currency" because of its involvement in intracellular energy transfers. For example, nicotinamide adenine dinucleotide (NAD), flavin adenine dinucleotide (FAD), and nicotinamide adenine dinucleotide phosphate (NADP) all contain
1340-408: A degree of crystallinity approaching zero or one will tend to be transparent, while polymers with intermediate degrees of crystallinity will tend to be opaque due to light scattering by crystalline or glassy regions. For many polymers, crystallinity may also be associated with decreased transparency. The space occupied by a polymer molecule is generally expressed in terms of radius of gyration , which
1474-587: A deviation from a simple linear chain. A branched polymer molecule is composed of a main chain with one or more substituent side chains or branches. Types of branched polymers include star polymers , comb polymers , polymer brushes , dendronized polymers , ladder polymers , and dendrimers . There exist also two-dimensional polymers (2DP) which are composed of topologically planar repeat units. A polymer's architecture affects many of its physical properties including solution viscosity, melt viscosity, solubility in various solvents, glass-transition temperature and
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#17328448562831608-464: A flexible quality. Plasticizers are also put in some types of cling film to make the polymer more flexible. The attractive forces between polymer chains play a large part in determining the polymer's properties. Because polymer chains are so long, they have many such interchain interactions per molecule, amplifying the effect of these interactions on the polymer properties in comparison to attractions between conventional molecules. Different side groups on
1742-479: A given application, the properties of a polymer can be tuned or enhanced by combination with other materials, as in composites . Their application allows to save energy (lighter cars and planes, thermally insulated buildings), protect food and drinking water (packaging), save land and lower use of fertilizers (synthetic fibres), preserve other materials (coatings), protect and save lives (hygiene, medical applications). A representative, non-exhaustive list of applications
1876-402: A high surface quality and are also highly transparent so that the laser properties are dominated by the laser dye used to dope the polymer matrix. These type of lasers, that also belong to the class of organic lasers , are known to yield very narrow linewidths which is useful for spectroscopy and analytical applications. An important optical parameter in the polymer used in laser applications
2010-404: A limit on the number of torsion angles possible in the structure. Conformers of closed form riboses differ in regards to how the lone oxygen in the molecule is positioned respective to the nitrogenous base (also known as a nucleobase or just a base) attached to the ribose. If a carbon is facing towards the base, then the ribose is labeled as endo. If a carbon is facing away from the base, then
2144-679: A negative charge each, making RNA a charged molecule (polyanion). The 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 binding to each other in a bulge, or the GNRA tetraloop that has a guanine–adenine base-pair. The chemical structure of RNA is very similar to that of DNA , but differs in three primary ways: Like DNA, most biologically active RNAs, including mRNA , tRNA , rRNA , snRNAs , and other non-coding RNAs , contain self-complementary sequences that allow parts of
2278-437: 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. Reverse transcribing viruses replicate their genomes by 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
2412-642: 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 and plastids . It tags proteins encoded by mRNAs that lack stop codons for degradation and prevents the ribosome from stalling. The earliest known regulators of gene expression were proteins known as repressors and activators – regulators with specific short binding sites within enhancer regions near
2546-545: 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
2680-496: A number of RNA-dependent RNA polymerases that use RNA as their template for synthesis of a new strand of RNA. For instance, a number of RNA viruses (such as poliovirus) 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. Many RNAs are involved in modifying other RNAs. Introns are spliced out of pre-mRNA by spliceosomes , which contain several small nuclear RNAs (snRNA), or
2814-457: A pathogen and determine which molecular parts to extract, inactivate, and use in a vaccine. Small molecules with conventional therapeutic properties can target RNA and DNA structures, thereby treating novel diseases. However, research is scarce on small molecules targeting RNA and approved drugs for human illness. Ribavirin, branaplam, and ataluren are currently available medications that stabilize double-stranded RNA structures and control splicing in
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#17328448562832948-447: A planar molecule on paper. Despite this, it is typically non-planar in nature. Even between hydrogen atoms, the many constituents on a ribose molecule cause steric hindrance and strain between them. To relieve this crowding and ring strain , the ring puckers, i.e. becomes non-planar. This puckering is achieved by displacing an atom from the plane, relieving the strain and yielding a more stable conformation. Puckering, otherwise known as
3082-401: A polymer behaves as a continuous macroscopic material. They are classified as bulk properties, or intensive properties according to thermodynamics . The bulk properties of a polymer are those most often of end-use interest. These are the properties that dictate how the polymer actually behaves on a macroscopic scale. The tensile strength of a material quantifies how much elongating stress
3216-421: A polymer is its first and most important attribute. Polymer nomenclature is generally based upon the type of monomer residues comprising the polymer. A polymer which contains only a single type of repeat unit is known as a homopolymer , while a polymer containing two or more types of repeat units is known as a copolymer . A terpolymer is a copolymer which contains three types of repeat units. Polystyrene
3350-433: A polymeric material can be described at different length scales, from the sub-nm length scale up to the macroscopic one. There is in fact a hierarchy of structures, in which each stage provides the foundations for the next one. The starting point for the description of the structure of a polymer is the identity of its constituent monomers. Next, the microstructure essentially describes the arrangement of these monomers within
3484-536: A process called reptation in which each chain molecule is constrained by entanglements with neighboring chains to move within a virtual tube. The theory of reptation can explain polymer molecule dynamics and viscoelasticity . Depending on their chemical structures, polymers may be either semi-crystalline or amorphous. Semi-crystalline polymers can undergo crystallization and melting transitions , whereas amorphous polymers do not. In polymers, crystallization and melting do not suggest solid-liquid phase transitions, as in
3618-427: A result, they typically have lower melting temperatures than other polymers. When a polymer is dispersed or dissolved in a liquid, such as in commercial products like paints and glues, the chemical properties and molecular interactions influence how the solution flows and can even lead to self-assembly of the polymer into complex structures. When a polymer is applied as a coating, the chemical properties will influence
3752-466: A role in the development of C. elegans . Studies on RNA interference earned a Nobel Prize for Andrew Fire and Craig Mello in 2006, and another Nobel 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 for research on RNA, in 2009 it
3886-415: A role in the activation of the innate immune system against viral infections. 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 circRNA ). circRNAs are thought to arise via a "back-splice" reaction where the spliceosome joins a upstream 3' acceptor to a downstream 5' donor splice site. So far
4020-454: A specific sequence on the messenger RNA chain through hydrogen bonding. Ribosomal RNA (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 , and one is synthesized elsewhere. In the cytoplasm, ribosomal RNA and protein combine to form
4154-429: A specific spatial tertiary structure . The scaffold for this structure is provided by secondary structural elements that are hydrogen bonds within the molecule. This leads to several recognizable "domains" of secondary structure like hairpin loops , bulges, and internal loops . In order to create, i.e., design, RNA for any given secondary structure, two or three bases would not be enough, but four bases are enough. This
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4288-456: A statistical distribution of chain lengths, the molecular weight is expressed in terms of weighted averages. The number-average molecular weight ( M n ) and weight-average molecular weight ( M w ) are most commonly reported. The ratio of these two values ( M w / M n ) is the dispersity ( Đ ), which is commonly used to express the width of the molecular weight distribution. The physical properties of polymer strongly depend on
4422-480: A stimulative or inhibitory hormone receptor is activated by a signal molecule . These receptors are linked to a stimulative or inhibitory regulative G-protein . When a stimulative G-protein is activated, adenylyl cyclase catalyzes ATP into cAMP by using Mg or Mn . cAMP, a secondary messenger, then goes on to activate protein kinase A , which is an enzyme that regulates cell metabolism . Protein kinase A regulates metabolic enzymes by phosphorylation which causes
4556-537: A tendency to form amorphous and semicrystalline structures rather than crystals . Polymers are studied in the fields of polymer science (which includes polymer chemistry and polymer physics ), biophysics and materials science and engineering . Historically, products arising from the linkage of repeating units by covalent chemical bonds have been the primary focus of polymer science. An emerging important area now focuses on supramolecular polymers formed by non-covalent links. Polyisoprene of latex rubber
4690-432: A variety of different but structurally related monomer residues; for example, polynucleotides such as DNA are composed of four types of nucleotide subunits. A polymer containing ionizable subunits (e.g., pendant carboxylic groups ) is known as a polyelectrolyte or ionomer , when the fraction of ionizable units is large or small respectively. The microstructure of a polymer (sometimes called configuration) relates to
4824-800: A variety of disorders. Protein-coding mRNAs have emerged as new therapeutic candidates, with RNA replacement being particularly beneficial for brief but torrential protein expression. In vitro transcribed mRNAs (IVT-mRNA) have been used to deliver proteins for bone regeneration, pluripotency, and heart function in animal models. SiRNAs, short RNA molecules, play a crucial role in innate defense against viruses and chromatin structure. They can be artificially introduced to silence specific genes, making them valuable for gene function studies, therapeutic target validation, and drug development. mRNA vaccines have emerged as an important new class of vaccines, using mRNA to manufacture proteins which provoke an immune response. Their first successful large-scale application came in
4958-405: A wide-meshed cross-linking between the "main chains". Close-meshed crosslinking, on the other hand, leads to thermosets . Cross-links and branches are shown as red dots in the figures. Highly branched polymers are amorphous and the molecules in the solid interact randomly. An important microstructural feature of a polymer is its architecture and shape, which relates to the way branch points lead to
5092-401: Is protein synthesis , a universal function in which RNA molecules direct the synthesis of proteins on ribosomes . This process uses transfer RNA ( tRNA ) molecules to deliver amino acids to the ribosome , where ribosomal RNA ( rRNA ) then links amino acids together to form coded proteins. It has become widely accepted in science that early in the history of life on Earth , prior to
5226-423: Is a ribozyme . Each nucleotide in RNA contains a ribose sugar, with carbons numbered 1' through 5'. A base is attached to the 1' position, in general, adenine (A), cytosine (C), guanine (G), or uracil (U). Adenine and guanine are purines , and cytosine and uracil are pyrimidines . A phosphate group is attached to the 3' position of one ribose and the 5' position of the next. The phosphate groups have
5360-814: Is a substance or material that consists of very large molecules, or macromolecules , that are constituted by many repeating subunits derived from one or more species of monomers . Due to their broad spectrum of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers . Their consequently large molecular mass , relative to small molecule compounds , produces unique physical properties including toughness , high elasticity , viscoelasticity , and
5494-479: Is a crucial physical parameter for polymer manufacturing, processing, and use. Below T g , molecular motions are frozen and polymers are brittle and glassy. Above T g , molecular motions are activated and polymers are rubbery and viscous. The glass-transition temperature may be engineered by altering the degree of branching or crosslinking in the polymer or by the addition of plasticizers . Whereas crystallization and melting are first-order phase transitions ,
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5628-410: Is a long-chain n -alkane. There are also branched macromolecules with a main chain and side chains, in the case of polyethylene the side chains would be alkyl groups . In particular unbranched macromolecules can be in the solid state semi-crystalline, crystalline chain sections highlighted red in the figure below. While branched and unbranched polymers are usually thermoplastics, many elastomers have
5762-400: Is also commonly present in polymer backbones, such as those of polyethylene glycol , polysaccharides (in glycosidic bonds ), and DNA (in phosphodiester bonds ). Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain or network. During the polymerization process, some chemical groups may be lost from each monomer. This happens in
5896-512: Is an average distance from the center of mass of the chain to the chain itself. Alternatively, it may be expressed in terms of pervaded volume , which is the volume spanned by the polymer chain and scales with the cube of the radius of gyration. The simplest theoretical models for polymers in the molten, amorphous state are ideal chains . Polymer properties depend of their structure and they are divided into classes according to their physical bases. Many physical and chemical properties describe how
6030-481: Is an example of a natural polymer, and the polystyrene of styrofoam is an example of a synthetic polymer. In biological contexts, essentially all biological macromolecules —i.e., proteins (polyamides), nucleic acids (polynucleotides), and polysaccharides —are purely polymeric, or are composed in large part of polymeric components. The term "polymer" derives from Greek πολύς (polus) 'many, much' and μέρος (meros) 'part'. The term
6164-569: Is assembled as a chain of nucleotides . Cellular organisms use messenger RNA ( mRNA ) to convey genetic information (using the nitrogenous bases of guanine , uracil , adenine , and cytosine , denoted by the letters G, U, A, and C) that directs synthesis of specific proteins. Many viruses encode their genetic information using an RNA genome . Some RNA molecules play an active role within cells by catalyzing biological reactions, controlling gene expression , or sensing and communicating responses to cellular signals. One of these active processes
6298-490: 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. At first, regulatory RNA
6432-428: Is composed only of styrene -based repeat units, and is classified as a homopolymer. Polyethylene terephthalate , even though produced from two different monomers ( ethylene glycol and terephthalic acid ), is usually regarded as a homopolymer because only one type of repeat unit is formed. Ethylene-vinyl acetate contains more than one variety of repeat unit and is a copolymer. Some biological polymers are composed of
6566-503: Is correlated with a decrease in immune stimulation. Along with phosphorylation, ribofuranose molecules can exchange their oxygen with selenium and sulfur to produce similar sugars that only vary at the 4' position. These derivatives are more lipophilic than the original molecule. Increased lipophilicity makes these species more suitable for use in techniques such as PCR , RNA aptamer post-modification, antisense technology , and for phasing X-ray crystallographic data. Similar to
6700-409: Is defined, for small strains , as the ratio of rate of change of stress to strain. Like tensile strength, this is highly relevant in polymer applications involving the physical properties of polymers, such as rubber bands. The modulus is strongly dependent on temperature. Viscoelasticity describes a complex time-dependent elastic response, which will exhibit hysteresis in the stress-strain curve when
6834-463: Is derived from ribose; it contains one ribose, three phosphate groups, and an adenine base. ATP is created during cellular respiration from adenosine diphosphate (ATP with one less phosphate group). Ribose is a building block in secondary signaling molecules such as cyclic adenosine monophosphate (cAMP) which is derived from ATP. One specific case in which cAMP is used is in cAMP-dependent signaling pathways . In cAMP signaling pathways, either
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#17328448562836968-407: Is given below. Ribose Ribose is a simple sugar and carbohydrate with molecular formula C 5 H 10 O 5 and the linear-form composition H−(C=O)−(CHOH) 4 −H. The naturally occurring form, d -ribose , is a component of the ribonucleotides from which RNA is built, and so this compound is necessary for coding , decoding , regulation and expression of genes . It has
7102-417: Is likely why nature has "chosen" a four base alphabet: fewer than four would not allow the creation of all structures, while more than four bases are not necessary to do so. Since RNA is charged, metal ions such as Mg are needed to stabilise many secondary and tertiary structures . The naturally occurring enantiomer of RNA is D -RNA composed of D -ribonucleotides. All chirality centers are located in
7236-584: Is present in pyranose forms (α:β = 1:2) and 24% in the furanose forms (α:β = 1:3), with only about 0.1% of the linear form present. The ribonucleosides adenosine , cytidine , guanosine , and uridine are all derivatives of β- d -ribofuranose. Metabolically important species that include phosphorylated ribose include ADP , ATP , coenzyme A , and NADH . cAMP and cGMP serve as secondary messengers in some signaling pathways and are also ribose derivatives. The ribose moiety appears in some pharmaceutical agents, including
7370-413: Is processed to mature mRNA. This removes its introns —non-coding sections of the pre-mRNA. 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 . In prokaryotic cells, which do not have nucleus and cytoplasm compartments, mRNA can bind to ribosomes while it is being transcribed from DNA. After
7504-479: Is synthesized from ATP and ribose 5-phosphate by an enzyme called PRPP synthetase . Ribokinase catalyzes the conversion of d -ribose to d -ribose 5-phosphate . Once converted, d -ribose-5-phosphate is available for the manufacturing of the amino acids tryptophan and histidine , or for use in the pentose phosphate pathway . The absorption of d -ribose is 88–100% in the small intestines (up to 200 mg/kg·h). One important modification occurs at
7638-435: Is the change in refractive index with temperature also known as dn/dT. For the polymers mentioned here the (dn/dT) ~ −1.4 × 10 in units of K in the 297 ≤ T ≤ 337 K range. Most conventional polymers such as polyethylene are electrical insulators , but the development of polymers containing π-conjugated bonds has led to a wealth of polymer-based semiconductors , such as polythiophenes . This has led to many applications in
7772-563: Is the main constituent of wood and paper. Hemoglycin (previously termed hemolithin ) is a space polymer that is the first polymer of amino acids found in meteorites . The list of synthetic polymers , roughly in order of worldwide demand, includes polyethylene , polypropylene , polystyrene , polyvinyl chloride , synthetic rubber , phenol formaldehyde resin (or Bakelite ), neoprene , nylon , polyacrylonitrile , PVB , silicone , and many more. More than 330 million tons of these polymers are made every year (2015). Most commonly,
7906-545: Is used as template for building the ends of eukaryotic chromosomes . 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 viruses ( double-stranded RNA viruses ). Double-stranded RNA, such as viral RNA or siRNA , can trigger RNA interference in eukaryotes , as well as interferon response in vertebrates . In eukaryotes, double-stranded RNA (dsRNA) plays
8040-500: Is used in biochemistry and biology to refer to all of these forms, though more specific names for each are used when required. In its linear form, ribose can be recognised as the pentose sugar with all of its hydroxyl functional groups on the same side in its Fischer projection . d -Ribose has these hydroxyl groups on the right hand side and is associated with the systematic name (2 R ,3 R ,4 R )-2,3,4,5-tetrahydroxypentanal, whilst l -ribose has its hydroxyl groups appear on
8174-545: 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 . Like other structured biopolymers 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 circuit topology . 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
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#17328448562838308-726: The d -ribofuranose moiety . They can each be derived from d -ribose after it is converted to d -ribose 5-phosphate by the enzyme ribokinase . NAD, FAD, and NADP act as electron acceptors in biochemical redox reactions in major metabolic pathways including glycolysis , the citric acid cycle , fermentation , and the electron transport chain . Nucleotides are synthesized through salvage or de novo synthesis . Nucleotide salvage uses pieces of previously made nucleotides and re-synthesizes them for future use. In de novo, amino acids, carbon dioxide, folate derivatives, and phosphoribosyl pyrophosphate (PRPP) are used to synthesize nucleotides. Both de novo and salvage require PRPP which
8442-491: The RNA World theory. There are indications that the enterobacterial sRNAs are involved in various cellular processes and seem to have significant role in stress responses such as membrane stress, starvation stress, phosphosugar stress and DNA damage. Also, it has been suggested that sRNAs have been evolved to have important role in stress responses because of their kinetic properties that allow for rapid response and stabilisation of
8576-447: The amino acid sequence in the 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 RNAs ("ncRNA") can be encoded by their own genes (RNA genes), but can also derive from mRNA introns . The most prominent examples of non-coding RNAs are transfer RNA (tRNA) and ribosomal RNA (rRNA), both of which are involved in
8710-572: The galactic center of the Milky Way Galaxy . RNA, initially deemed unsuitable for therapeutics due to its short half-life, has been made useful through advances in stabilization. Therapeutic applications arise as RNA folds into complex conformations and binds proteins, nucleic acids, and small molecules to form catalytic centers. RNA-based vaccines are thought to be easier to produce than traditional vaccines derived from killed or altered pathogens, because it can take months or years to grow and study
8844-410: The genetic code . There are more than 100 other naturally occurring modified nucleosides. The greatest structural diversity of modifications can be found in 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
8978-417: The pentose phosphate pathway , an energy-producing pathway, to produce d -ribose-5-phosphate. The enzyme glucose-6-phosphate-dehydrogenase (G-6-PDH) is often in short supply in cells, but more so in diseased tissue, such as in myocardial cells in patients with cardiac disease. The supply of d -ribose in the mitochondria is directly correlated with ATP production; decreased d -ribose supply reduces
9112-467: The 2' modifications in nature, a synthetic modification of ribose includes the addition of fluorine at the 2' position. This fluorinated ribose acts similar to the methylated ribose because it is capable of suppressing immune stimulation depending on the location of the ribose in the DNA strand. The big difference between methylation and fluorination, is the latter only occurs through synthetic modifications. The addition of fluorine leads to an increase in
9246-467: The 2006 Nobel Prize in Physiology or Medicine for discovering microRNAs (miRNAs), specific short RNA molecules that can base-pair with mRNAs. Post-transcriptional expression levels of many genes can be controlled by RNA interference , in which miRNAs , specific short RNA molecules, pair with mRNA regions and target them for degradation. This antisense -based process involves steps that first process
9380-422: 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 RNAs are often modified by enzymes after transcription. For example, a poly(A) tail and a 5' cap are added to eukaryotic pre-mRNA and introns are removed by the spliceosome . There are also
9514-555: 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. The functional form of single-stranded RNA molecules, just like proteins, frequently requires
9648-544: The C2' position of the ribose molecule. By adding an O-alkyl group, the nuclear resistance of the RNA is increased because of additional stabilizing forces. These forces are stabilizing because of the increase of intramolecular hydrogen bonding and an increase in the glycosidic bond stability. The resulting increase of resistance leads to increases in the half-life of siRNA and the potential therapeutic potential in cells and animals. The methylation of ribose at particular sites
9782-496: The DNA to RNA and subsequently translate that information to synthesize the specified protein from amino acids . The protein may be modified further following translation in order to provide appropriate structure and functioning. There are other biopolymers such as rubber , suberin , melanin , and lignin . Naturally occurring polymers such as cotton , starch , and rubber were familiar materials for years before synthetic polymers such as polyethene and perspex appeared on
9916-764: The RNA so that it can base-pair with a region of its target mRNAs. Once the base pairing occurs, other proteins direct the mRNA to be destroyed by nucleases . Next to be linked to regulation were 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 silencing of blocks of chromatin via recruitment of 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 . The third major group of regulatory RNAs
10050-408: 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 (like enzymes). For instance, determination of the structure of
10184-502: The RNAs mature. 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 ). Another notable modified base is hypoxanthine , a deaminated adenine base whose nucleoside is called inosine (I). Inosine plays a key role in the wobble hypothesis of
10318-441: The adhesion of the coating and how it interacts with external materials, such as superhydrophobic polymer coatings leading to water resistance. Overall the chemical properties of a polymer are important elements for designing new polymeric material products. Polymers such as PMMA and HEMA:MMA are used as matrices in the gain medium of solid-state dye lasers , also known as solid-state dye-doped polymer lasers. These polymers have
10452-567: The amount of ATP being produced. Studies suggest that supplementing d -ribose following tissue ischemia (e.g. myocardial ischemia) increases myocardial ATP production, and therefore mitochondrial function. Essentially, administering supplemental d -ribose bypasses an enzymatic step in the pentose phosphate pathway by providing an alternate source of 5-phospho- d -ribose 1- pyrophosphate for ATP production. Supplemental d -ribose enhances recovery of ATP levels while also reducing cellular injury in humans and other animals. One study suggested that
10586-462: The antibiotics neomycin and paromomycin . Ribose as its 5-phosphate ester is typically produced from glucose by the pentose phosphate pathway . In at least some archaea, alternative pathways have been identified. Ribose can be synthesized chemically, but commercial production relies on fermentation of glucose. Using genetically modified strains of B. subtilis , 90 g/liter of ribose can be produced from 200 g of glucose. The conversion entails
10720-434: The backbone in a variety of ways. A copolymer containing a controlled arrangement of monomers is called a sequence-controlled polymer . Alternating, periodic and block copolymers are simple examples of sequence-controlled polymers . Tacticity describes the relative stereochemistry of chiral centers in neighboring structural units within a macromolecule. There are three types of tacticity: isotactic (all substituents on
10854-442: The case of the 5S rRNA of the members of the genus Halococcus ( Archaea ), which have an insertion, thus increasing its size. Messenger RNA (mRNA) carries information about a protein sequence to the ribosomes , the protein synthesis factories in the cell. It is coded so that every three nucleotides (a codon ) corresponds to one amino acid. In eukaryotic cells, once precursor mRNA (pre-mRNA) has been transcribed from DNA, it
10988-421: The case of water or other molecular fluids. Instead, crystallization and melting refer to the phase transitions between two solid states ( i.e. , semi-crystalline and amorphous). Crystallization occurs above the glass-transition temperature ( T g ) and below the melting temperature ( T m ). All polymers (amorphous or semi-crystalline) go through glass transitions . The glass-transition temperature ( T g )
11122-402: The cell nucleus and is usually catalyzed by an enzyme— 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 activity of the enzyme. The enzyme then progresses along the template strand in
11256-469: The continuously linked backbone of a polymer used for the preparation of plastics consists mainly of carbon atoms. A simple example is polyethylene ('polythene' in British English), whose repeat unit or monomer is ethylene . Many other structures do exist; for example, elements such as silicon form familiar materials such as silicones, examples being Silly Putty and waterproof plumbing sealant. Oxygen
11390-536: The degree of crystallinity may be expressed in terms of a weight fraction or volume fraction of crystalline material. Few synthetic polymers are entirely crystalline. The crystallinity of polymers is characterized by their degree of crystallinity, ranging from zero for a completely non-crystalline polymer to one for a theoretical completely crystalline polymer. Polymers with microcrystalline regions are generally tougher (can be bent more without breaking) and more impact-resistant than totally amorphous polymers. Polymers with
11524-400: The driving force for mixing is usually entropy , not interaction energy. In other words, miscible materials usually form a solution not because their interaction with each other is more favorable than their self-interaction, but because of an increase in entropy and hence free energy associated with increasing the amount of volume available to each component. This increase in entropy scales with
11658-440: 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 . In May 2022, scientists discovered that RNA can form spontaneously on prebiotic basalt lava glass , presumed to have been abundant on the early Earth . In March 2015, DNA and RNA nucleobases , including uracil , cytosine and thymine , were reportedly formed in
11792-414: The evolution of DNA and possibly of protein-based enzymes as well, an " RNA world " existed in which RNA served as both living organisms' storage method for genetic information —a role fulfilled today by DNA, except in the case of RNA viruses —and potentially performed catalytic functions in cells—a function performed today by protein enzymes, with the notable and important exception of the ribosome, which
11926-417: The field of organic electronics . Nowadays, synthetic polymers are used in almost all walks of life. Modern society would look very different without them. The spreading of polymer use is connected to their unique properties: low density, low cost, good thermal/electrical insulation properties, high resistance to corrosion, low-energy demanding polymer manufacture and facile processing into final products. For
12060-454: 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 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
12194-460: The form of COVID-19 vaccines during the COVID-19 pandemic . Polymer A polymer is a substance composed of macromolecules. A macromolecule is a molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units derived, actually or conceptually, from molecules of low relative molecular mass. A polymer ( / ˈ p ɒ l ɪ m ər / )
12328-527: The free energy of mixing for polymer solutions and thereby making solvation less favorable, and thereby making the availability of concentrated solutions of polymers far rarer than those of small molecules. Furthermore, the phase behavior of polymer solutions and mixtures is more complex than that of small molecule mixtures. Whereas most small molecule solutions exhibit only an upper critical solution temperature phase transition (UCST), at which phase separation occurs with cooling, polymer mixtures commonly exhibit
12462-422: The function of circRNAs is largely unknown, although for few examples a microRNA sponging activity has been demonstrated. Research on RNA has led to many important biological discoveries and numerous Nobel Prizes . Nucleic acids were discovered in 1868 by Friedrich Miescher , who called the material 'nuclein' since it was found in the nucleus . It was later discovered that prokaryotic cells, which do not have
12596-548: 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 repressing genes post-transcriptionally , long non-coding RNAs shutting down blocks of chromatin epigenetically , and enhancer RNAs inducing increased gene expression. Bacteria and archaea have also been shown to use regulatory RNA systems such as bacterial small RNAs and CRISPR . Fire and Mello were awarded
12730-401: The glass transition is not. The glass transition shares features of second-order phase transitions (such as discontinuity in the heat capacity, as shown in the figure), but it is generally not considered a thermodynamic transition between equilibrium states. In general, polymeric mixtures are far less miscible than mixtures of small molecule materials. This effect results from the fact that
12864-415: The individual chains more strongly in position and resist deformations and matrix breakup, both at higher stresses and higher temperatures. Copolymers are classified either as statistical copolymers, alternating copolymers, block copolymers, graft copolymers or gradient copolymers. In the schematic figure below, Ⓐ and Ⓑ symbolize the two repeat units . Monomers within a copolymer may be organized along
12998-451: The intermediacy of gluconate and ribulose. Ribose has been detected in meteorites . Ribose is an aldopentose (a monosaccharide containing five carbon atoms that, in its open chain form, has an aldehyde functional group at one end). In the conventional numbering scheme for monosaccharides, the carbon atoms are numbered from C1' (in the aldehyde group) to C5'. The deoxyribose derivative found in DNA differs from ribose by having
13132-459: The introns can be ribozymes that are spliced by themselves. RNA can also be altered by having its nucleotides modified to nucleotides other than A , C , G and U . In eukaryotes, modifications of RNA nucleotides are in general directed by small nucleolar RNAs (snoRNA; 60–300 nt), found in the nucleolus and cajal bodies . snoRNAs associate with enzymes and guide them to a spot on an RNA by basepairing to that RNA. These enzymes then perform
13266-471: The laboratory under outer 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 been formed in red giants or in interstellar dust and gas clouds. In July 2022, astronomers reported massive amounts of prebiotic molecules , including possible RNA precursors, in
13400-451: The latter case, increasing the polymer chain length 10-fold would increase the viscosity over 1000 times. Increasing chain length furthermore tends to decrease chain mobility, increase strength and toughness, and increase the glass-transition temperature (T g ). This is a result of the increase in chain interactions such as van der Waals attractions and entanglements that come with increased chain length. These interactions tend to fix
13534-575: The left hand side in a Fischer projection. Cyclisation of ribose occurs via hemiacetal formation due to attack on the aldehyde by the C4' hydroxyl group to produce a furanose form or by the C5' hydroxyl group to produce a pyranose form. In each case, there are two possible geometric outcomes, named as α- and β- and known as anomers , depending on the stereochemistry at the hemiacetal carbon atom (the "anomeric carbon"). At room temperature, about 76% of d -ribose
13668-436: The length (or equivalently, the molecular weight) of the polymer chain. One important example of the physical consequences of the molecular weight is the scaling of the viscosity (resistance to flow) in the melt. The influence of the weight-average molecular weight ( M w {\displaystyle M_{w}} ) on the melt viscosity ( η {\displaystyle \eta } ) depends on whether
13802-417: The load is removed. Dynamic mechanical analysis or DMA measures this complex modulus by oscillating the load and measuring the resulting strain as a function of time. Transport properties such as diffusivity describe how rapidly molecules move through the polymer matrix. These are very important in many applications of polymers for films and membranes. The movement of individual macromolecules occurs by
13936-436: The market. Many commercially important polymers are synthesized by chemical modification of naturally occurring polymers. Prominent examples include the reaction of nitric acid and cellulose to form nitrocellulose and the formation of vulcanized rubber by heating natural rubber in the presence of sulfur . Ways in which polymers can be modified include oxidation , cross-linking , and end-capping . The structure of
14070-413: The material will endure before failure. This is very important in applications that rely upon a polymer's physical strength or durability. For example, a rubber band with a higher tensile strength will hold a greater weight before snapping. In general, tensile strength increases with polymer chain length and crosslinking of polymer chains. Young's modulus quantifies the elasticity of the polymer. It
14204-456: The name "ribose" as it is a partial rearrangement of the name of another sugar, arabinose , of which ribose is an epimer at the 2' carbon; both names also relate to gum arabic , from which arabinose was first isolated and from which they prepared l -ribose . Like most sugars, ribose exists as a mixture of cyclic forms in equilibrium with its linear form, and these readily interconvert especially in aqueous solution . The name "ribose"
14338-411: The north and south ranges. When only a single atom is displaced, it is referred to as an "envelope" pucker. When two atoms are displaced, it is referred to as a "twist" pucker, in reference to the zigzag orientation. In an "endo" pucker, the major displacement of atoms is on the β-face, the same side as the C4'-C5' bond and the base. In an "exo" pucker, the major displacement of atoms is on the α-face, on
14472-425: 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. Like DNA, RNA can carry genetic information. RNA viruses have genomes 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
14606-444: The number of particles (or moles) being mixed. Since polymeric molecules are much larger and hence generally have much higher specific volumes than small molecules, the number of molecules involved in a polymeric mixture is far smaller than the number in a small molecule mixture of equal volume. The energetics of mixing, on the other hand, is comparable on a per volume basis for polymeric and small molecule mixtures. This tends to increase
14740-421: The opposite side of the ring. The major forms of ribose are the 3'-endo pucker (commonly adopted by RNA and A-form DNA) and 2'-endo pucker (commonly adopted by B-form DNA). These ring puckers are developed from changes in ring torsion angles; there are infinite combinations of angles so therefore, there is an infinite number of transposable pucker conformations, each separated by disparate activation energies. ATP
14874-713: The partially negatively charged oxygen atoms in C=O groups on another. These strong hydrogen bonds, for example, result in the high tensile strength and melting point of polymers containing urethane or urea linkages. Polyesters have dipole-dipole bonding between the oxygen atoms in C=O groups and the hydrogen atoms in H-C groups. Dipole bonding is not as strong as hydrogen bonding, so a polyester's melting point and strength are lower than Kevlar 's ( Twaron ), but polyesters have greater flexibility. Polymers with non-polar units such as polyethylene interact only through weak Van der Waals forces . As
15008-422: The physical arrangement of monomer residues along the backbone of the chain. These are the elements of polymer structure that require the breaking of a covalent bond in order to change. Various polymer structures can be produced depending on the monomers and reaction conditions: A polymer may consist of linear macromolecules containing each only one unbranched chain. In the case of unbranched polyethylene, this chain
15142-686: The physiological state. Bacterial small RNAs generally act via 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 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. Synthesis of RNA typically occurs in
15276-399: The polymer and create gaps between polymer chains for greater mobility and fewer interchain interactions. A good example of the action of plasticizers is related to polyvinylchlorides or PVCs. A uPVC, or unplasticized polyvinylchloride, is used for things such as pipes. A pipe has no plasticizers in it, because it needs to remain strong and heat-resistant. Plasticized PVC is used in clothing for
15410-426: The polymer at the scale of a single chain. The microstructure determines the possibility for the polymer to form phases with different arrangements, for example through crystallization , the glass transition or microphase separation . These features play a major role in determining the physical and chemical properties of a polymer. The identity of the repeat units (monomer residues, also known as "mers") comprising
15544-540: The polymer can lend the polymer to ionic bonding or hydrogen bonding between its own chains. These stronger forces typically result in higher tensile strength and higher crystalline melting points. The intermolecular forces in polymers can be affected by dipoles in the monomer units. Polymers containing amide or carbonyl groups can form hydrogen bonds between adjacent chains; the partially positively charged hydrogen atoms in N-H groups of one chain are strongly attracted to
15678-403: The polymer is above or below the onset of entanglements . Below the entanglement molecular weight , η ∼ M w 1 {\displaystyle \eta \sim {M_{w}}^{1}} , whereas above the entanglement molecular weight, η ∼ M w 3.4 {\displaystyle \eta \sim {M_{w}}^{3.4}} . In
15812-583: The polymerization of PET polyester . The monomers are terephthalic acid (HOOC—C 6 H 4 —COOH) and ethylene glycol (HO—CH 2 —CH 2 —OH) but the repeating unit is —OC—C 6 H 4 —COO—CH 2 —CH 2 —O—, which corresponds to the combination of the two monomers with the loss of two water molecules. The distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue. Synthetic methods are generally divided into two categories, step-growth polymerization and chain polymerization . The essential difference between
15946-403: 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. Messenger RNA (mRNA) is the type of RNA that carries information from DNA to the ribosome , the sites of protein synthesis ( translation ) in the cell cytoplasm. The coding sequence of the mRNA determines
16080-921: The process of translation. There are also non-coding RNAs involved in gene regulation, RNA processing and other roles. Certain RNAs are able to catalyse chemical reactions such as cutting and ligating other RNA molecules, and the catalysis of peptide bond formation in the ribosome ; these are known as ribozymes . According to the length of RNA chain, RNA includes small RNA and long RNA. Usually, small RNAs are shorter than 200 nt in length, and long RNAs are greater than 200 nt long. Long RNAs, also called large RNAs, mainly include long non-coding RNA (lncRNA) and mRNA . Small RNAs mainly include 5.8S ribosomal RNA (rRNA), 5S rRNA , transfer RNA (tRNA), microRNA (miRNA), small interfering RNA (siRNA), small nucleolar RNA (snoRNAs), Piwi-interacting RNA (piRNA), tRNA-derived small RNA (tsRNA) and small rDNA-derived RNA (srRNA). There are certain exceptions as in
16214-400: The ribose is labeled as exo. If there is an oxygen molecule attached to the 2' carbon of a closed cycle ribose, then the exo confirmation is more stable because it decreases the interactions of the oxygen with the base. The difference itself is quite small, but when looking at an entire chain of RNA the slight difference amounts to a sizable impact. A ribose molecule is typically represented as
16348-506: The ribosome—an RNA-protein complex that catalyzes the assembly of proteins—revealed that its active site is composed entirely of RNA. 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 mostly take the A-form geometry , although in single strand dinucleotide contexts, RNA can rarely also adopt
16482-437: The same side), atactic (random placement of substituents), and syndiotactic (alternating placement of substituents). Polymer morphology generally describes the arrangement and microscale ordering of polymer chains in space. The macroscopic physical properties of a polymer are related to the interactions between the polymer chains. When applied to polymers, the term crystalline has a somewhat ambiguous usage. In some cases,
16616-512: The size of individual polymer coils in solution. A variety of techniques may be employed for the synthesis of a polymeric material with a range of architectures, for example living polymerization . A common means of expressing the length of a chain is the degree of polymerization , which quantifies the number of monomers incorporated into the chain. As with other molecules, a polymer's size may also be expressed in terms of molecular weight . Since synthetic polymerization techniques typically yield
16750-435: The stabilization of the glycosidic bond and an increase of intramolecular hydrogen bonds. d -ribose has been suggested for use in management of congestive heart failure (as well as other forms of heart disease) and for chronic fatigue syndrome (CFS), also called myalgic encephalomyelitis (ME) in an open-label non-blinded, non-randomized, and non-crossover subjective study. Supplemental d -ribose can bypass part of
16884-448: The states is known as a coil–globule transition . Inclusion of plasticizers tends to lower T g and increase polymer flexibility. Addition of the plasticizer will also modify dependence of the glass-transition temperature T g on the cooling rate. The mobility of the chain can further change if the molecules of plasticizer give rise to hydrogen bonding formation. Plasticizers are generally small molecules that are chemically similar to
17018-440: The sugar ring conformation (specifically ribose sugar), can be described by the amplitude of pucker as well as the pseudorotation angle. The pseudo-rotation angle can be described as either "north (N)" or "south (S)" range. While both ranges are found in double helices, the north range is commonly associated with RNA and the A form of DNA . In contrast, the south range is associated with B form DNA . Z-DNA contains sugars in both
17152-686: The term crystalline finds identical usage to that used in conventional crystallography . For example, the structure of a crystalline protein or polynucleotide, such as a sample prepared for x-ray crystallography , may be defined in terms of a conventional unit cell composed of one or more polymer molecules with cell dimensions of hundreds of angstroms or more. A synthetic polymer may be loosely described as crystalline if it contains regions of three-dimensional ordering on atomic (rather than macromolecular) length scales, usually arising from intramolecular folding or stacking of adjacent chains. Synthetic polymers may consist of both crystalline and amorphous regions;
17286-420: The torsion angles for the rotation encompassing the bonds influence the configuration of the respective nucleoside and nucleotide. The secondary structure of a nucleic acid is determined by the rotation of its 7 torsion angles . Having a large amount of torsion angles allows for greater flexibility. In closed ring riboses, the observed flexibility mentioned above is not observed because the ring cycle imposes
17420-555: The two is that in chain polymerization, monomers are added to the chain one at a time only, such as in polystyrene , whereas in step-growth polymerization chains of monomers may combine with one another directly, such as in polyester . Step-growth polymerization can be divided into polycondensation , in which low-molar-mass by-product is formed in every reaction step, and polyaddition . Newer methods, such as plasma polymerization do not fit neatly into either category. Synthetic polymerization reactions may be carried out with or without
17554-422: 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, introns and RNA splicing were discovered in both mammalian viruses and in cellular genes, resulting in
17688-553: Was awarded for the elucidation of the atomic structure of the ribosome to Venki Ramakrishnan , Thomas A. Steitz , and Ada Yonath . In 2023 the Nobel Prize in Physiology or Medicine was awarded to Katalin Karikó and Drew Weissman for their discoveries concerning modified nucleosides that enabled the development of effective mRNA vaccines against COVID-19. In 1968, Carl Woese hypothesized that RNA might be catalytic and suggested that
17822-605: Was coined in 1833 by Jöns Jacob Berzelius , though with a definition distinct from the modern IUPAC definition. The modern concept of polymers as covalently bonded macromolecular structures was proposed in 1920 by Hermann Staudinger , who spent the next decade finding experimental evidence for this hypothesis. Polymers are of two types: naturally occurring and synthetic or man made . Natural polymeric materials such as hemp , shellac , amber , wool , silk , and natural rubber have been used for centuries. A variety of other natural polymers exist, such as cellulose , which
17956-403: 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
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