1 Boardworks High School Science Monosaccharides
2 Introducing carbohydratesBoardworks High School Science Monosaccharides Carbohydrates are a group of substances used as both energy sources and structural materials in organisms. All carbohydrates contain carbon, hydrogen and oxygen, with the general formula: Cx(H2O)y. There are three main groups of carbohydrates: monosaccharides – these are simple sugars, with the general formula (CH20)n, where n can be 3–7 disaccharides – these are “double sugars”, formed from two monosaccharides polysaccharides – these are large molecules formed from many monosaccharides.
3 Boardworks High School Science MonosaccharidesGlucose Boardworks High School Science Monosaccharides Glucose is an abundant and very important monosaccharide. It contains six carbon atoms, so it is a hexose sugar. Its general formula is C6H12O6. Glucose is the major energy source for most cells. It is highly soluble and is the main form in which carbohydrates are transported around the body of animals. The structure of glucose can be represented in different ways: Teacher notes Students should familiarize themselves with all of these representations of glucose. straight chain ring ring (simplified)
4 Boardworks High School Science MonosaccharidesAlpha and beta glucose Boardworks High School Science Monosaccharides Glucose exists in different forms called structural isomers. Two common isomers are alpha glucose and beta glucose. 6 6 5 5 alpha glucose beta glucose 4 1 4 1 3 2 3 2 The only difference between these two isomers is the position of the –OH group attached to carbon 1. In alpha glucose it is below the carbon, and in beta glucose it is above the carbon. Teacher notes The red numbers refer to the carbon atoms. A six-membered ring containing five carbon atoms and one oxygen atom is called a pyranose ring. This minor structural difference has a major effect on the biological roles of alpha and beta glucose.
5 Fructose and galactoseBoardworks High School Science Monosaccharides Two other important hexose monosaccharides are fructose and galactose. fructose galactose Fructose is very soluble and is the main sugar in fruits and nectar. It is sweeter than glucose. Teacher notes Like glucose, fructose and galactose exist as alpha and beta structural isomers. Note that fructose is sometimes shown as a pyranose ring (i.e. with five rather than four carbon atoms in the ring) rather than the furanose ring shown here. Galactose is not as soluble as glucose and has an important role in the production of glycolipids and glycoproteins.
6 Boardworks High School Science MonosaccharidesPentoses Boardworks High School Science Monosaccharides Pentose monosaccharides contain five carbon atoms. Like hexoses, pentoses are long enough to form a ring. Two important pentose molecules are the structural isomers ribose and deoxyribose. These are important constituents of RNA and DNA. 5 5 1 4 4 1 3 2 3 2 Teacher notes The red numbers refer to the carbon atoms. A five-membered ring containing four carbon atoms and one oxygen atom is called a furanose ring. . ribose deoxyribose The only difference between them is that ribose has one H atom and one –OH group attached to carbon 2, whereas deoxyribose has 2 H atoms and no –OH group.
7 The formation of disaccharidesBoardworks High School Science Monosaccharides
8 Maltose, sucrose and lactoseBoardworks High School Science Monosaccharides Maltose (malt sugar) is formed from two glucose molecules joined by an alpha 1–4 glycosidic bond. Sucrose (table sugar) is formed from glucose and fructose joined by an alpha 1–4 glycosidic bond. Teacher notes Note that: maltose contains two alpha glucose molecules (hence the alpha glycosidic bond) sucrose contains alpha glucose (hence the alpha glycosidic bond) and beta fructose lactose contains beta galactose (hence the beta glycosidic bond) and alpha glucose The gray circle indicates the glycosidic bond. Lactose (milk sugar) is formed from galactose and glucose joined by a beta 1–4 glycosidic bond.
9 Benedict’s test for reducing sugarsBoardworks High School Science Monosaccharides
10 Mono- and disaccharidesBoardworks High School Science Monosaccharides