Science, Tech, Math › Science Monosaccharide Definition and Functions Share Flipboard Email Print Fructose is an example of a monosaccharide. PASIEKA / Getty Images Science Chemistry Biochemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated January 13, 2020 A monosaccharide or simple sugar is a carbohydrate that cannot be hydrolyzed into smaller carbohydrates. Like all carbohydrates, a monosaccharide consists of three chemical elements: carbon, hydrogen, and oxygen. It is the simplest type of carbohydrate molecule and often serves as the basis for forming more complex molecules. Monosaccharides include aldoses, ketoses, and their derivatives. The general chemical formula for a monosaccharide is CnH2nOn or (CH2O)n. Examples of monosaccharides include the three most common forms: glucose (dextrose), fructose (levulose), and galactose. Key Takeaways: Monosaccharides Monosaccharides are the smallest carbohydrate molecules. They cannot be broken down into simpler carbohydrates, so they are also called simple sugars.Examples of monosaccharides include glucose, fructose, ribose, xylose, and mannose.The two main functions of monosaccharides in the body are energy storage and as the building blocks of more complex sugars that are used as structural elements.Monosaccharides are crystalline solids that are soluble in water and usually have a sweet taste. Properties In pure form, monosaccharides are crystalline, water-soluble, colorless solids. Monosaccharides have a sweet flavor because the orientation of the OH group interacts with the taste receptor on the tongue that detects sweetness. Via a dehydration reaction, two monosaccharides can form a disaccharide, three to ten can form an oligosaccharide, and more than ten can form a polysaccharide. Functions Monosaccharides serve two main functions within a cell. They are used to store and produce energy. Glucose is a particularly important energy molecule. Energy is released when its chemical bonds are broken. Monosaccharides are also used as building blocks to form more complex sugars, which are important structural elements. Structure and Nomenclature The chemical formula (CH2O)n indicates a monosaccharide is a carbon hydrate. However, the chemical formula doesn't indicate the placement of the carbon atom within the molecule or the chirality of the sugar. Monosaccharides are classified based on how many carbon atoms they contain, the placement of the carbonyl group, and their stereochemistry. The n in the chemical formula indicates the number of carbon atoms in a monosaccharide. Each simple sugar contains three or more carbon atoms. They are categorized by the number of carbons: triose (3), tetrose (4), pentose (5), hexose (6), and heptose (7). Note, all of these classes are named with the -ose ending, indicating they are carbohydrates. Glyceraldehyde is a triose sugar. Erythrose and threose are examples of tetrose sugars. Ribose and xylose are examples of pentose sugars. The most abundant simple sugars are hexose sugars. These include glucose, fructose, mannose, and galactose. Sedoheptulose and mannoheptulose are examples of heptose monosaccharides. Aldoses have more than one hydroxyl group (-OH) and a carbonyl group (C=O) at the terminal carbon, while ketoses have the hydroxyl group and carbonyl group attached to the second carbon atom. The classification systems may be combined to describe a simple sugar. For example, glucose is an aldohexose, while ribose is a ketohexose. Linear vs. Cyclic Monosaccharides may exist as straight-chain (acyclic) molecules or as rings (cyclic). The ketone or aldehyde group of a straight molecule can reversibly react with a hydroxyl group on another carbon to form a heterocyclic ring. In the ring, an oxygen atom bridges two carbon atoms. Rings made of five atoms are called furanose sugars, while those consisting of six atoms are the pyranose form. In nature, the straight-chain, furanose, and pyranose forms exist in equilibrium. Calling a molecule "glucose" could refer to straight-chain glucose, glucofuranose, glucopyranose, or a mixture of the forms. Ribose exists in both straight-chain and cyclic forms. Bacsica / Getty Images Stereochemistry Monosaccharides exhibit stereochemistry. Each simple sugar can be in either D- (dextro) or L- (levo) form. The D- and L- forms are mirror images of each other. Natural monosaccharides are in the D- form, while synthetically produced monosaccharides are usually in the L-form. The D- and L- forms of glucose share a chemical formula, but are oriented differently. NEUROtiker / public domain Cyclic monosaccharides also display stereochemistry. The -OH group replacing oxygen from the carbonyl group can be in one of two positions (commonly drawn above or below the ring). The isomers are indicated using the prefixes α- and β-. Sources Fearon, W.F. (1949). Introduction to Biochemistry (2nd ed.). London: Heinemann. ISBN 9781483225395.IUPAC (1997) Compendium of Chemical Terminology (2nd ed.). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications. Oxford. doi:10.1351/goldbook.M04021 ISBN 0-9678550-9-8.McMurry, John. (2008). Organic Chemistry (7th ed.). Belmont, CA: Thomson Brooks/Cole.Pigman, W.; Horton, D. (1972). "Chapter 1: Stereochemistry of the Monosaccharides". In Pigman and Horton (ed.). The Carbohydrates: Chemistry and Biochemistry Vol 1A (2nd ed.). San Diego: Academic Press. ISBN 9780323138338.Solomon, E.P.; Berg, L.R.; Martin, D.W. (2004). Biology. Cengage Learning. ISBN 978-0534278281.