Monosaccharide - wikipedia Monosaccharide hide This article has multiple issues. Please help improve it or discuss these issues on the talk page. ( Learn how and when to remove these template messages ) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( July 2009 ) This article only describes one highly specialized aspect of its associated subject. Please help improve this article by adding more general information. The talk page may contain suggestions. ( September 2013 ) Monosaccharides ( / ˌmɒnoʊˈsækəraɪd, ˌmɒnə - /, from Greek monos : single, sacchar : sugar ), also called simple sugars, are the most basic units of carbohydrates. They are fundamental units of carbohydrates and can not be further hydrolyzed to simpler compounds. The general formula is C O. They are the simplest form of sugar and are usually colorless, water - soluble, and crystalline solids. Some monosaccharides have a sweet taste. Examples of monosaccharides include glucose ( dextrose ), fructose ( levulose ), and galactose. Monosaccharides are the building blocks of disaccharides ( such as sucrose and lactose ) and polysaccharides ( such as cellulose and starch ). Further, each carbon atom that supports a hydroxyl group ( so, all of the carbons except for the primary and terminal carbon ) is chiral, giving rise to a number of isomeric forms, all with the same chemical formula. For instance, galactose and glucose are both aldohexoses, but have different physical structures and chemical properties. Contents 1 Structure and nomenclature 1.1 Linear - chain monosaccharides 1.2 Open - chain stereoisomers 1.3 Configuration of monosaccharides 1.4 Cyclisation of Monosaccharides 1.5 Haworth projection 2 Derivatives 3 See also 4 Notes 5 References 6 External links Structure and nomenclature With few exceptions ( e.g., deoxyribose ), monosaccharide have this chemical formula : C ( H O ), where conventionally x ≥ 3. Monosaccharides can be classified by the number x of carbon atoms they contain : triose ( 3 ), tetrose ( 4 ), pentose ( 5 ), hexose ( 6 ), heptose ( 7 ), and so on. The most important monosaccharide, glucose, is a hexose. Examples of heptoses include the ketoses, mannoheptulose and sedoheptulose. Monosaccharides with eight or more carbons are rarely observed as they are quite unstable. In aqueous solutions monosaccharides exist as rings if they have more than four carbons. Linear - chain monosaccharides Simple monosaccharides have a linear and unbranched carbon skeleton with one carbonyl ( C = O ) functional group, and one hydroxyl ( OH ) group on each of the remaining carbon atoms. Therefore, the molecular structure of a simple monosaccharide can be written as H ( CHOH ) ( C = O ) ( CHOH ) H, where n + 1 + m = x ; so that its elemental formula is C H O. By convention, the carbon atoms are numbered from 1 to x along the backbone, starting from the end that is closest to the C =O group. Monnosaccharides are the simplest units of carbohydrates and the simplest form of sugar. If the carbonyl is at position 1 ( that is, n or m is zero ), the molecule begins with a formyl group H ( C = O ) − and is technically an aldehyde. In that case, the compound is termed an aldose. Otherwise, the molecule has a keto group, a carbonyl − ( C = O ) − between two carbons ; then it is formally a ketone, and is termed a ketose. Ketoses of biological interest usually have the carbonyl at position 2. The various classifications above can be combined, resulting in names such as `` aldohexose '' and `` ketotriose ''. A more general nomenclature for open - chain monosaccharides combines a Greek prefix to indicate the number of carbons ( tri -, tetr -, pent -, hex -, etc. ) with the suffixes `` - ose '' for aldoses and `` - ulose '' for ketoses. In the latter case, if the carbonyl is not at position 2, its position is then indicated by a numeric infix. So, for example, H ( C = O ) ( CHOH ) H is pentose, H ( CHOH ) ( C = O ) ( CHOH ) H is pentulose, and H ( CHOH ) ( C = O ) ( CHOH ) H is pent - 3 - ulose. Open - chain stereoisomers Two monosaccharides with equivalent molecular graphs ( same chain length and same carbonyl position ) may still be distinct stereoisomers, whose molecules differ in the three - dimensional arrangement of the bonds of certain atoms. This happens only if the molecule contains a stereogenic center, specifically a carbon atom that is chiral ( connected to four distinct molecular sub-structures ). Those four bonds can have any of two configurations in space distinguished by their handedness. In a simple open - chain monosaccharide, every carbon is chiral except the first and the last atoms of the chain, and ( in ketoses ) the carbon with the keto group. For example, the triketose H ( CHOH ) ( C = O ) ( CHOH ) H ( glycerone, dihydroxyacetone ) has no stereogenic center, and therefore exists as a single stereoisomer. The other triose, the aldose H ( C = O ) ( CHOH ) H ( glyceraldehyde ), has one chiral carbon -- the central one, number 2 -- which is bonded to groups − H, − OH, − C ( OH ) H, and − ( C = O ) H. Therefore, it exists as two stereoisomers whose molecules are mirror images of each other ( like a left and a right glove ). Monosaccharides with four or more carbons may contain multiple chiral carbons, so they typically have more than two stereoisomers. The number of distinct stereoisomers with the same diagram is bounded by 2, where c is the total number of chiral carbons. The Fischer projection is a systematic way of drawing the skeletal formula of an acyclic monosaccharide so that the handedness of each chiral carbon is well specified. Each stereoisomer of a simple open - chain monosaccharide can be identified by the positions ( right or left ) in the Fischer diagram of the chiral hydroxyls ( the hydroxyls attached to the chiral carbons ). Most stereoisomers are themselves chiral ( distinct from their mirror images ). In the Fischer projection, two mirror - image isomers differ by having the positions of all chiral hydroxyls reversed right - to - left. Mirror - image isomers are chemically identical in non-chiral environments, but usually have very different biochemical properties and occurrences in nature. While most stereoisomers can be arranged in pairs of mirror - image forms, there are some non-chiral stereoisomers that are identical to their mirror images, in spite of having chiral centers. This happens whenever the molecular graph is symmetrical, as in the 3 - ketopentoses H ( CHOH ) ( CO ) ( CHOH ) H, and the two halves are mirror images of each other. In that case, mirroring is equivalent to a half - turn rotation. For this reason, there are only three distinct 3 - ketopentose stereoisomers, even though the molecule has two chiral carbons. Distinct stereoisomers that are not mirror - images of each other usually have different chemical properties, even in non-chiral environments. Therefore, each mirror pair and each non-chiral stereoisomer may be given a specific monosaccharide name. For example, there are 16 distinct aldohexose stereoisomers, but the name `` glucose '' means a specific pair of mirror - image aldohexoses. In the Fischer projection, one of the two glucose isomers has the hydroxyl at left on C3, and at right on C4 and C5 ; while the other isomer has the reversed pattern. These specific monosaccharide names have conventional three - letter abbreviations, like `` Glu '' for glucose and `` Thr '' for threose. Generally, a monosaccharide with n asymmetrical carbons has 2 stereoisomers. The number of open chain stereoisomers for an aldose monosaccharide is larger by one than that of a ketose monosaccharide of the same length. Every ketose will have 2 stereoisomers where n > 2 is the number of carbons. Every aldose will have 2 stereoisomers where n > 2 is the number of carbons. These are also referred to as epimers which have the different arrangement of − OH and − H groups at the asymmetric or chiral carbon atoms ( this does not apply to those carbons having the carbonyl functional group ). Configuration of monosaccharides Like many chiral molecules, the two stereoisomers of glyceraldehyde will gradually rotate the polarization direction of linearly polarized light as it passes through it, even in solution. The two stereoisomers are identified with the prefixes D - and L -, according to the sense of rotation : D - glyceraldehyde is dextrorotatory ( rotates the polarization axis clockwise ), while L - glyceraldehyde is levorotatory ( rotates it counterclockwise ). D - and L - glucose The D - and L - prefixes are also used with other monosaccharides, to distinguish two particular stereoisomers that are mirror - images of each other. For this purpose, one considers the chiral carbon that is furthest removed from the C =O group. Its four bonds must connect to − H, − OH, − C ( OH ) H, and the rest of the molecule. If the molecule can be rotated in space so that the directions of those four groups match those of the analog groups in D - glyceraldehyde 's C2, then the isomer receives the D - prefix. Otherwise, it receives the L - prefix. In the Fischer projection, the D - and L - prefixes specifies the configuration at the carbon atom that is second from bottom : D - if the hydroxyl is on the right side, and L - if it is on the left side. Note that the D - and L - prefixes do not indicate the direction of rotation of polarized light, which is a combined effect of the arrangement at all chiral centers. However, the two enantiomers will always rotate the light in opposite directions, by the same amount. See also d / l system. Cyclisation of monosaccharides A monosaccharide often switches from the acyclic ( open - chain ) form to a cyclic form, through a nucleophilic addition reaction between the carbonyl group and one of the hydroxyls of the same molecule. The reaction creates a ring of carbon atoms closed by one bridging oxygen atom. The resulting molecule has an hemiacetal or hemiketal group, depending on whether the linear form was an aldose or a ketose. The reaction is easily reversed, yielding the original open - chain form. In these cyclic forms, the ring usually has 5 or 6 atoms. These forms are called furanoses and pyranoses, respectively -- by analogy with furan and pyran, the simplest compounds with the same carbon - oxygen ring ( although they lack the double bonds of these two molecules ). For example, the aldohexose glucose may form a hemiacetal linkage between the hydroxyl on carbon 1 and the oxygen on carbon 4, yielding a molecule with a 5 - membered ring, called glucofuranose. The same reaction can take place between carbons 1 and 5 to form a molecule with a 6 - membered ring, called glucopyranose. Cyclic forms with a 7 - atom ring ( the same of oxepane ), rarely encountered, are called heptoses. Conversion between the furanose, acyclic, and pyranose forms of D - glucose. Pyranose forms of some pentose sugars. Pyranose forms of some hexose sugars. For many monosaccharides ( including glucose ), the cyclic forms predominate, in the solid state and in solutions, and therefore the same name commonly is used for the open - and closed - chain isomers. Thus, for example, the term `` glucose '' may signify glucofuranose, glucopyranose, the open - chain form, or a mixture of the three. Cyclization creates a new stereogenic center at the carbonyl - bearing carbon. The − OH group that replaces the carbonyl 's oxygen may end up in two distinct positions relative to the ring 's midplane. Thus each open - chain monosaccharide yields two cyclic isomers ( anomers ), denoted by the prefixes α - and β -. The molecule can change between these two forms by a process called mutarotation, that consists in a reversal of the ring - forming reaction followed by another ring formation. Haworth projection The stereochemical structure of a cyclic monosaccharide can be represented in a Haworth projection. In this diagram, the α - isomer for the pyranose form of a D - aldohexose has the - OH of the anomeric carbon below the plane of the carbon atoms, while the β - isomer has the - OH of the anomeric carbon above the plane. Pyranoses typically adopt a chair conformation, similar to that of cyclohexane. In this conformation, the α - isomer has the - OH of the anomeric carbon in an axial position, whereas the β - isomer has the OH - of the anomeric carbon in equatorial position ( considering D - aldohexose sugars ). α - D - Glucopyranose β - D - Glucopyranose Derivatives A large number of biologically important modified monosaccharides exist : Amino sugars such as : Galactosamine Glucosamine Sialic acid N - Acetylglucosamine Sulfosugars such as : Sulfoquinovose others ascorbic acid mannitol See also Reducing sugar Sugar acid Sugar alcohol Disaccharide Notes Jump up ^ `` Carbohydrates ''. Chemistry for Biologists. Royal Society of Chemistry. Retrieved 10 March 2017. Jump up ^ `` Carbohydrates ''. Chemistry for Biologists. Royal Society of Chemistry. Retrieved 10 March 2017. Jump up ^ Pigman, William Ward ; Anet, E.F.L.J. ( 1972 ). `` Chapter 4 : Mutarotations and Actions of Acids and Bases ''. In Pigman and Horton. The Carbohydrates : Chemistry and Biochemistry Vol 1A ( 2nd ed. ). San Diego : Academic Press. pp. 165 -- 194. Jump up ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. ( the `` Gold Book '' ) ( 1997 ). Online corrected version : ( 2006 -- ) `` Haworth representation ''. References McMurry, John. Organic Chemistry. 7th ed. Belmont, CA : Thomson Brooks / Cole, 2008. Print. External links Look up monosaccharide in Wiktionary, the free dictionary. Nomenclature of Carbohydrates Types of carbohydrates General Aldose Ketose Furanose Pyranose Geometry Anomer Cyclohexane conformation Mutarotation Monosaccharides Dioses Aldodiose Glycolaldehyde Trioses Aldotriose Glyceraldehyde Ketotriose Dihydroxyacetone Tetroses Aldotetroses Erythrose Threose Ketotetrose Erythrulose Pentoses Aldopentoses Arabinose Lyxose Ribose Xylose Ketopentoses Ribulose Xylulose Deoxy sugars Deoxyribose Hexoses Aldohexoses Allose Altrose Galactose Glucose Gulose Idose Mannose Talose Ketohexoses Fructose Psicose Sorbose Tagatose Deoxy sugars Fucose Fuculose Rhamnose Heptoses Ketoheptoses Mannoheptulose Sedoheptulose Above 7 Octoses Nonoses Neuraminic acid Multiple Disaccharides Cellobiose Isomaltose Isomaltulose Lactose Lactulose Maltose Sucrose Trehalose Turanose Trisaccharides Maltotriose Melezitose Raffinose Tetrasaccharides Stachyose Other oligosaccharides Acarbose Fructooligosaccharide ( FOS ) Galactooligosaccharide ( GOS ) Isomaltooligosaccharide ( IMO ) Maltodextrin Polysaccharides Beta - glucan Oat beta - glucan Lentinan Sizofiran Zymosan Cellulose Chitin Chitosan Dextrin / Dextran Fructose / Fructan Inulin Galactose / Galactan Glucose / Glucan Glycogen Hemicellulose Levan beta 2 → 6 Lignin Mannan Pectin Starch Amylopectin Amylose Xanthan gum GND : 4170482 - 4 LCCN : sh85086973 NDL : 00572703 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Monosaccharide&oldid=845603559 '' Categories : Monosaccharides Carbohydrate chemistry Hidden categories : Articles needing additional references from July 2009 All articles needing additional references Wikipedia articles needing context from September 2013 Articles with multiple maintenance issues Wikipedia articles with GND identifiers Wikipedia articles with LCCN identifiers Wikipedia articles with NDL identifiers Talk Contents About Wikipedia Asturianu Azərbaycanca বাংলা Bân - lâm - gú Беларуская Беларуская ( тарашкевіца ) ‎ Български Bosanski Català Čeština Deutsch Eesti Ελληνικά Español Esperanto Euskara فارسی Français Frysk Gaeilge Galego 한국어 Հայերեն हिन्दी Hrvatski Ido Bahasa Indonesia Íslenska Italiano עברית Қазақша Kurdî Кыргызча Latviešu Lietuvių Magyar Македонски Bahasa Melayu Nederlands 日本 語 Norsk Norsk nynorsk Occitan Polski Português Română Русский Scots Shqip Simple English Slovenčina Slovenščina Српски / srpski Srpskohrvatski / српскохрватски Basa Sunda Suomi Svenska தமிழ் ไทย Türkçe Українська Tiếng Việt 粵語 中文 56 more Edit links This page was last edited on 12 June 2018, at 22 : 02 ( UTC ). 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Question: the minimum number of carbon in a monosaccharide is
Answer: 3