Configuration of Monosaccharides
The configuration of monosaccharides refers to the spatial arrangement of atoms around the asymmetric carbon atoms in the molecule. Monosaccharides can have different configurations, such as D or L, based on the orientation of the hydroxyl group on the chiral carbon farthest from the carbonyl group. This configuration is important in determining the properties and functions of monosaccharides in biological systems.
6 Key excerpts on "Configuration of Monosaccharides"
eBook - ePub- James N. BeMiller(Author)
- 2018(Publication Date)
...A chiral carbon atom is a carbon atom that can exist in two different spatial arrangements (configurations). Chiral carbon atoms can be recognized easily because they are carbon atoms that have each of their four tetrahedral bonds connected to different atoms or groups of atoms. The two different arrangements of the four groups in space (configurations) are what are called nonsuperimposable mirror images (Fig. 1.1). In other words, one is the reflection of the other that one would see in a mirror, with everything on the right in one configuration on the left in the other and vice versa (Box 1.2). Monosaccharides are carbohydrate molecules that cannot be broken down by hydrolysis 2 into simpler (smaller) carbohydrate molecules. Hence, monosaccharides are at times referred to as “simple sugars” or just :sugars," which infers that they are the simplest (smallest) of the carbohydrates. (The term saccharide is derived from saccharose, which is an old term for cane sugar. Now, it refers to any carbohydrate, especially a monosaccharide; but as subsequent chapters on oligo- and polysaccharides indicate, it can be applied to any size carbohydrate. Mono is derived from the Greek word for one. In chemistry, it often means containing only one, so the term monosaccharide means one saccharide or one sugar, indicating that it is a molecule composed of only one sugar unit and not of two or more sugar units joined together). Monosaccharides are the monomeric units of oligosaccharides (Chapter 3) and polysaccharides (Chapter 4), both of which contain more than one saccharide (sugar) unit and can be hydrolyzed to release their constituent monosaccharides. The common monosaccharides used as building blocks for oligo- and polysaccharides found in foods contain a group termed as the saccharose group. Figure 1.1 Chiral carbon atom. (A), (B), (D), and (E) represent different atoms or functional groups 2 attached to carbon atom (C)...
- Kim S Suvarna, Christopher Layton, John D. Bancroft(Authors)
- 2018(Publication Date)
- Elsevier(Publisher)
...Typical monosaccharides have the empirical formula (CH 2 O) n, where n is a value between 3 and 9. Glucose (Fig. 13.1) is a six-carbon simple carbohydrate which is not charged or ionized and referred to as a neutral sugar. Other neutral sugars include mannose, galactose and fructose. Monosaccharides contain asymmetric carbons referred to as chiral centers and the letters D or L at the beginning of a name refer to the structure of one of the chiral carbons within the molecule. D -Monosaccharides predominate in nature. The high numbers of hydroxyl (OH) groups present in the monosaccharide make most of them extremely water soluble. The majority of monosaccharides within a tissue specimen are lost during fixation and tissue processing due to their small size and water solubility and, as a result are not easily demonstrated by most histochemical techniques. The basic monosaccharide structure however, represents the building blocks of larger, more complex carbohydrates. The chemical and physical properties of the polysaccharides and glycoconjugates are largely determined by the types of monosaccharide which make up these molecules and the various reactive groups within them. Polysaccharides These are large macromolecules composed of multiple monosaccharides joined by covalent bonds known as glycosidic linkages. Fig. 13.2 demonstrates an α1–4 glycosidic linkage connecting two units of glucose which is the predominant linkage in the polysaccharides starch and glycogen. Additionally, some of the glucose units of these polysaccharides may have more than one glycosidic linkage, forming a branching structure resembling a tree. Starch and glycogen are large macromolecules with molecular weights exceeding 1 x 10 6 Daltons...
eBook - ePubBiochemistry
An Organic Chemistry Approach
- Michael B. Smith(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...The general carbohydrate structure shown above contains one carbohydrate unit and it is categorized as a monosaccharide. If two monosaccharides are coupled together, the resulting molecule is a disaccharide and a molecule with three monosaccharide units is a trisaccharide. The structures shown for the disaccharide show both the open-chain form (A) and the pyranose form (B ; see Section 13.2 and Figure 13.4), as discussed in Section 14.2. Likewise, the trisaccharide is shown as the open-chain form (C) and the pyranose form (D), as discussed in Section 14.2. Linking 5–15 monosaccharides yields an oligosaccharide. A polysaccharide has > 15 monosaccharides linked together. Note that in both disaccharides and trisaccharides the monosaccharides are linked together by an acetal linkage (Sections 3.7 and 7.5.A). 13.2 Monosaccharides Monosaccharide glycose derivatives are the main focus, but the other categories of carbohydrates will be discussed. Glycoses are subdivided into aldoses where the carbonyl unit is an aldehyde, and ketoses, where the carbonyl unit is a ketone. This discussion begins with the characteristics and properties of glycoses, their structures, and how to name them. The basic unit of a glycose is shown, and there are several different monosaccharide glycoses. The carbon of each hydroxymethyl (CHOH) unit is a stereogenic center, so there are several diastereomers for most carbohydrates. Each time a CH 2 OH unit is added, another stereogenic center is added, which increases the number of diastereomers. Each diastereomer will have a (+) and a (–) form (enantiomers). For the glycose where n = 1 (three carbons) there is one stereogenic center and there are two stereoisomers (the two enantiomers), following the 2 n rule (Section 1.18)...
eBook - ePub- Jose Perez-Castineira(Author)
- 2020(Publication Date)
- De Gruyter(Publisher)
...Most naturally occurring sugars are D (Figure 3.2, Table 3.1). The classical D-L terminology for isomerism preceding the trivial names of monosaccharides (and aminoacids, as we shall see in Chapter 4) is preferred by biochemists over the Cahn–Ingold–Prelog rules [ 8 ]. The latter is more systematic, but rather cumbersome for these compounds, thus, the IUPAC systematic name for D-glucose would be (2 R,3 S,4 R,5 R)-2,3,4,5,6-pentahydroxyhexanal. Table 3.1: Some monosaccharides of nutritional interest. Sources Pentoses L-Arabinose Plant exudates, hemicelluloses, pectines (dietary fiber) D-Xylose Hemicelluloses (dietary fiber) 2-deoxy-D-ribose DNA D-ribose RNA Aldohexoses L-Fucose (6-deoxy-L-galactose) Human milk, plant exudates, and mucous membranes D-Galactose Milk (as lactose), oligo- and polysaccharides, cerebrosides D-Glucose Frequent and ubiquitous (sugar, milk, starch, cellulose …) D-Mannose Homo- or heteropolysaccharides, glycoconjugates Ketohexoses (or hexuloses) D-Fructose Fruits, honey, sacarose The most abundant in human nutrition are underlined. 3.2.2 Cyclic forms of monosaccharides Monosaccharides are readily soluble in water due to the presence of hydroxyl groups that form hydrogen bonds with the surrounding water molecules. In aqueous solutions, monosaccharides exist as an equilibrium mixture of acyclic and cyclic forms. In the latter, one of the hydroxyl groups reacts with the carbonyl group producing cyclic hemiacetals (Figure 3.3). Five- and six-membered rings are structurally favoured, the former being named furanoses and the latter pyranoses...
eBook - ePub- David Hames, Nigel Hooper(Authors)
- 2011(Publication Date)
- Taylor & Francis(Publisher)
...SECTION J – CARBOHYDRATE METABOLISM J1 Monosaccharides and disaccharides Key Notes Aldoses and ketoses A monosaccharide has the general formula (CH 2 O) n and contains either an aldehyde group (an aldose) or a ketone group (a ketose). The free aldehyde or ketone group can reduce cupric ions (Cu 2+) to cuprous ions (Cu +) and hence such a monosaccharide is called a reducing sugar. Stereoisomers The D and L stereoisomers of sugars refer to the configuration of the asymmetric carbon atom furthest from the aldehyde or ketone group. The sugar is said to be a D isomer if the configuration of the atoms bonded to this carbon atom is the same as for the asymmetric carbon in D -glyceraldehyde. Ring structures Tetroses and larger sugars can cyclize by reaction of the aldehyde or ketone group with a hydroxyl group on another carbon atom of the sugar. Glucose mainly cyclizes to form a six-membered pyranose ring whilst other sugars form five-membered furanose rings. Two forms (anomers) of D -glucopyranose exist, depending on whether the hydroxyl group attached to the anomeric carbon atom (C-1) lies below the plane of the ring (the α form) or above the plane of the ring (β form). In solution, the α and β forms interconvert via the open-chain form (mutarotation). The pyranose ring can exist in either boat or chair conformations but the chair form predominates since the side groups, which are usually OH groups, are less sterically hindered in this conformation. Disaccharides A disaccharide is formed when two monosaccharides become joined by a glycosidic bond. The bond may be an α- or β-bond depending on the configuration of the anomeric carbon atom involved in the bond. Usually the anomeric carbon atom of only one of the two monosaccharides is involved in the bond so that the disaccharide still has one free aldehyde or ketone group and is still reducing...
eBook - ePub- Raymond S. Ochs(Author)
- 2021(Publication Date)
- CRC Press(Publisher)
...4 Carbohydrates Carbohydrates are most commonly encountered as the sweetener sucrose and as starch, the nutrient of bread and pasta. The carbohydrates are literally hydrates of carbon, having the empirical formula (CH 2 O) n. Because they possess both hydroxyl and carbonyl groups, they are a step up in complexity from lipids. Unlike lipids, carbohydrates are generally very soluble in water. The Latin word for sugar is saccharide ; this is commonly used in the term polysaccharides. Sugars are nutrients for both animals and plants. Animals use sugars for rapid (i.e., minute-to-minute) energy production and lipids for long-term storage. Plants use sugars for energy exclusively, except at the seed stage. Sugars have greater weight than lipids, making them less suitable for long-term energy storage for organisms with mobile lifestyles (i.e., animals and seeds). The reason for the greater mass of sugars is two-fold. Sugars contain more oxygen atoms and are thus denser than lipids. Sugars also associate with water (through hydrogen bonding), further increasing their weight. Aside from providing energy, sugars have a wide variety of roles once they are chemically modified, such as cell–cell recognition and signaling. The specificity of blood group types derives from sugars attached to membrane lipids of red blood cells. Proteins secreted from cells are usually covalently linked to sugars. Thus, sugars are integral to biological function. We begin our study of sugars with the simplest ones: the monosaccharides. 4.1 Monosaccharides Monosaccharides have a single carbonyl group, which occurs at the first or second carbon atom. All remaining carbons have an attached hydroxyl group. There are two classes of monosaccharides: aldoses and ketoses. Aldoses (aldehydes) have the carbonyl at carbon one, whereas ketoses (ketones) have the carbonyl at carbon two. The “-ose” suffix (as in aldose and ketose) usually indicates that a compound is a sugar...
