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IUPAC name D-Ribose | |||
Systematic IUPAC name (2R,3R,4S,5R)-5-(hydroxymethyl)oxolane-2,3,4-triol | |||
Other names d-Ribose | |||
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Properties [1] [2] | |||
C5H10O5 | |||
Molar mass | 150.13 | ||
Appearance | White solid | ||
Melting point | 95 °C (203 °F; 368 K) | ||
100 g/L (25 °C, 77 °F) | |||
Chiral rotation ([α]D) | −21.5° (H2O) | ||
Related compounds | |||
Related aldopentoses | Arabinose Xylose Lyxose | ||
Related compounds | Deoxyribose | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). |
Ribose is a simple sugar and carbohydrate with molecular formula C5H10O5 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 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. [3] 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. [4] [5] [6] Fischer chose 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. [6] [7]
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. [8] The name "ribose" 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 (2R,3R,4R)-2,3,4,5-tetrahydroxypentanal, [9] whilst l-ribose has its hydroxyl groups appear on 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 is present in pyranose forms [8] : 228 (α:β = 1:2) [10] and 24% in the furanose forms [8] : 228 (α:β = 1:3), [10] with only about 0.1% of the linear form present. [11] [12]
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, [8] : 228–229 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 the antibiotics neomycin and paromomycin. [10]
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. [13]
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 the intermediacy of gluconate and ribulose. [14]
Ribose has been detected in meteorites. [15] [16]
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 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%). [11]
For ribose residues in nucleosides and nucleotide, 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. [17] 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 a limit on the number of torsion angles possible in the structure. [17] 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 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. [17] 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 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. [18] This puckering is achieved by displacing an atom from the plane, relieving the strain and yielding a more stable conformation. [17] Puckering, otherwise known as 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 the north and south ranges. [19] 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. [20] 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 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). [21] 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 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 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 Mg2+ or Mn2+. 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 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.[ citation needed ] For example, nicotinamide adenine dinucleotide (NAD), flavin adenine dinucleotide (FAD), and nicotinamide adenine dinucleotide phosphate (NADP) all contain 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. [22] [23] 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. [24] 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. [24] Both de novo and salvage require PRPP which is synthesized from ATP and ribose 5-phosphate by an enzyme called PRPP synthetase. [24]
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). [25]
One important modification occurs at 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. [26] The resulting increase of resistance leads to increases in the half-life of siRNA and the potential therapeutic potential in cells and animals. [27] The methylation of ribose at particular sites is correlated with a decrease in immune stimulation. [28]
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. [27]
Similar to 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. [26] The big difference between methylation and fluorination, is the latter only occurs through synthetic modifications. The addition of fluorine leads to an increase in the stabilization of the glycosidic bond and an increase of intramolecular hydrogen bonds. [26]
d-ribose has been suggested for use in management of congestive heart failure [29] (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. [30]
Supplemental d-ribose can bypass part of 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 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 the use of supplemental d-ribose reduces the instance of angina in men with diagnosed coronary artery disease. [31] d-Ribose has been used to treat many pathological conditions, such as chronic fatigue syndrome, fibromyalgia, and myocardial dysfunction. It is also used to reduce symptoms of cramping, pain, stiffness, etc. after exercise and to improve athletic performance[ citation needed ].
Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology, and metabolism. Over the last decades of the 20th century, biochemistry has become successful at explaining living processes through these three disciplines. Almost all areas of the life sciences are being uncovered and developed through biochemical methodology and research. Biochemistry focuses on understanding the chemical basis which allows biological molecules to give rise to the processes that occur within living cells and between cells, in turn relating greatly to the understanding of tissues and organs as well as organism structure and function. Biochemistry is closely related to molecular biology, the study of the molecular mechanisms of biological phenomena.
Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). If the sugar is ribose, the polymer is RNA; if the sugar is deoxyribose, a variant of ribose, the polymer is DNA.
Nucleotides are organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules within all life-forms on Earth. Nucleotides are obtained in the diet and are also synthesized from common nutrients by the liver.
In chemistry, a pentose is a monosaccharide with five carbon atoms. The chemical formula of many pentoses is C
5H
10O
5, and their molecular weight is 150.13 g/mol.
Adenine is a purine nucleotide base. It is one of the four nucleobases in the nucleic acids of DNA, the other three being guanine (G), cytosine (C), and thymine (T). Adenine derivatives have various roles in biochemistry including cellular respiration, in the form of both the energy-rich adenosine triphosphate (ATP) and the cofactors nicotinamide adenine dinucleotide (NAD), flavin adenine dinucleotide (FAD) and Coenzyme A. It also has functions in protein synthesis and as a chemical component of DNA and RNA. The shape of adenine is complementary to either thymine in DNA or uracil in RNA.
Deoxyribose, or more precisely 2-deoxyribose, is a monosaccharide with idealized formula H−(C=O)−(CH2)−(CHOH)3−H. Its name indicates that it is a deoxy sugar, meaning that it is derived from the sugar ribose by loss of a hydroxy group. Discovered in 1929 by Phoebus Levene, deoxyribose is most notable for its presence in DNA. Since the pentose sugars arabinose and ribose only differ by the stereochemistry at C2′, 2-deoxyribose and 2-deoxyarabinose are equivalent, although the latter term is rarely used because ribose, not arabinose, is the precursor to deoxyribose.
A glycosidic bond or glycosidic linkage is a type of ether bond that joins a carbohydrate (sugar) molecule to another group, which may or may not be another carbohydrate.
In chemistry, a phosphodiester bond occurs when exactly two of the hydroxyl groups in phosphoric acid react with hydroxyl groups on other molecules to form two ester bonds. The "bond" involves this linkage C−O−PO−2O−C. Discussion of phosphodiesters is dominated by their prevalence in DNA and RNA, but phosphodiesters occur in other biomolecules, e.g. acyl carrier proteins, phospholipids and the cyclic forms of GMP and AMP.
In biochemistry, a ribonucleotide is a nucleotide containing ribose as its pentose component. It is considered a molecular precursor of nucleic acids. Nucleotides are the basic building blocks of DNA and RNA. Ribonucleotides themselves are basic monomeric building blocks for RNA. Deoxyribonucleotides, formed by reducing ribonucleotides with the enzyme ribonucleotide reductase (RNR), are essential building blocks for DNA. There are several differences between DNA deoxyribonucleotides and RNA ribonucleotides. Successive nucleotides are linked together via phosphodiester bonds.
The term amphibolism is used to describe a biochemical pathway that involves both catabolism and anabolism. Catabolism is a degradative phase of metabolism in which large molecules are converted into smaller and simpler molecules, which involves two types of reactions. First, hydrolysis reactions, in which catabolism is the breaking apart of molecules into smaller molecules to release energy. Examples of catabolic reactions are digestion and cellular respiration, where sugars and fats are broken down for energy. Breaking down a protein into amino acids, or a triglyceride into fatty acids, or a disaccharide into monosaccharides are all hydrolysis or catabolic reactions. Second, oxidation reactions involve the removal of hydrogens and electrons from an organic molecule. Anabolism is the biosynthesis phase of metabolism in which smaller simple precursors are converted to large and complex molecules of the cell. Anabolism has two classes of reactions. The first are dehydration synthesis reactions; these involve the joining of smaller molecules together to form larger, more complex molecules. These include the formation of carbohydrates, proteins, lipids and nucleic acids. The second are reduction reactions, in which hydrogens and electrons are added to a molecule. Whenever that is done, molecules gain energy.
A nucleoside triphosphate is a nucleoside containing a nitrogenous base bound to a 5-carbon sugar, with three phosphate groups bound to the sugar. They are the molecular precursors of both DNA and RNA, which are chains of nucleotides made through the processes of DNA replication and transcription. Nucleoside triphosphates also serve as a source of energy for cellular reactions and are involved in signalling pathways.
Biosynthesis, i.e., chemical synthesis occurring in biological contexts, is a term most often referring to multi-step, enzyme-catalyzed processes where chemical substances absorbed as nutrients serve as enzyme substrates, with conversion by the living organism either into simpler or more complex products. Examples of biosynthetic pathways include those for the production of amino acids, lipid membrane components, and nucleotides, but also for the production of all classes of biological macromolecules, and of acetyl-coenzyme A, adenosine triphosphate, nicotinamide adenine dinucleotide and other key intermediate and transactional molecules needed for metabolism. Thus, in biosynthesis, any of an array of compounds, from simple to complex, are converted into other compounds, and so it includes both the catabolism and anabolism of complex molecules. Biosynthetic processes are often represented via charts of metabolic pathways. A particular biosynthetic pathway may be located within a single cellular organelle, while others involve enzymes that are located across an array of cellular organelles and structures.
Transketolase is an enzyme that, in humans, is encoded by the TKT gene. It participates in both the pentose phosphate pathway in all organisms and the Calvin cycle of photosynthesis. Transketolase catalyzes two important reactions, which operate in opposite directions in these two pathways. In the first reaction of the non-oxidative pentose phosphate pathway, the cofactor thiamine diphosphate accepts a 2-carbon fragment from a 5-carbon ketose (D-xylulose-5-P), then transfers this fragment to a 5-carbon aldose (D-ribose-5-P) to form a 7-carbon ketose (sedoheptulose-7-P). The abstraction of two carbons from D-xylulose-5-P yields the 3-carbon aldose glyceraldehyde-3-P. In the Calvin cycle, transketolase catalyzes the reverse reaction, the conversion of sedoheptulose-7-P and glyceraldehyde-3-P to pentoses, the aldose D-ribose-5-P and the ketose D-xylulose-5-P.
Phoebus Aaron Theodore Levene was a Russian-born American biochemist who studied the structure and function of nucleic acids. He characterized the different forms of nucleic acid, DNA from RNA, and found that DNA contained adenine, guanine, thymine, cytosine, deoxyribose, and a phosphate group.
Sugar phosphates are often used in biological systems to store or transfer energy. They also form the backbone for DNA and RNA. Sugar phosphate backbone geometry is altered in the vicinity of the modified nucleotides.
Directionality, in molecular biology and biochemistry, is the end-to-end chemical orientation of a single strand of nucleic acid. In a single strand of DNA or RNA, the chemical convention of naming carbon atoms in the nucleotide pentose-sugar-ring means that there will be a 5′ end, which frequently contains a phosphate group attached to the 5′ carbon of the ribose ring, and a 3′ end, which typically is unmodified from the ribose -OH substituent. In a DNA double helix, the strands run in opposite directions to permit base pairing between them, which is essential for replication or transcription of the encoded information.
Nucleic acid metabolism is a collective term that refers to the variety of chemical reactions by which nucleic acids are either synthesized or degraded. Nucleic acids are polymers made up of a variety of monomers called nucleotides. Nucleotide synthesis is an anabolic mechanism generally involving the chemical reaction of phosphate, pentose sugar, and a nitrogenous base. Degradation of nucleic acids is a catabolic reaction and the resulting parts of the nucleotides or nucleobases can be salvaged to recreate new nucleotides. Both synthesis and degradation reactions require multiple enzymes to facilitate the event. Defects or deficiencies in these enzymes can lead to a variety of diseases.
Ribose 5-phosphate (R5P) is both a product and an intermediate of the pentose phosphate pathway. The last step of the oxidative reactions in the pentose phosphate pathway is the production of ribulose 5-phosphate. Depending on the body's state, ribulose 5-phosphate can reversibly isomerize to ribose 5-phosphate. Ribulose 5-phosphate can alternatively undergo a series of isomerizations as well as transaldolations and transketolations that result in the production of other pentose phosphates as well as fructose 6-phosphate and glyceraldehyde 3-phosphate.
Sucrose phosphorylase is an important enzyme in the metabolism of sucrose and regulation of other metabolic intermediates. Sucrose phosphorylase is in the class of hexosyltransferases. More specifically it has been placed in the retaining glycoside hydrolases family although it catalyzes a transglycosidation rather than hydrolysis. Sucrose phosphorylase catalyzes the conversion of sucrose to D-fructose and α-D-glucose-1-phosphate. It has been shown in multiple experiments that the enzyme catalyzes this conversion by a double displacement mechanism.
Ribose-5-phosphate isomerase (Rpi) encoded by the RPIA gene is an enzyme that catalyzes the conversion between ribose-5-phosphate (R5P) and ribulose-5-phosphate (Ru5P). It is a member of a larger class of isomerases which catalyze the interconversion of chemical isomers. It plays a vital role in biochemical metabolism in both the pentose phosphate pathway and the Calvin cycle. The systematic name of this enzyme class is D-ribose-5-phosphate aldose-ketose-isomerase.