Monosaccharide

Monosaccharides, sometimes known as "simple sugars," are the basic building blocks of carbohydrates. Most monosaccharides are colorless and water soluble, and some are sweet to taste. The monosaccharides familiar to most people are glucose and fructose, both of which are present as ingredients in many types of food. Monosaccharides contain varying numbers of carbon atoms, and this is used as a means of categorizing monosaccharides. Monosaccharides with two carbon atoms are diose, those with three carbon atoms are triose, those with four carbon atoms are tetrose, and so on. Glucose is a hexose monosaccharide because it contains six carbon atoms. It is difficult to find monosaccharides with more than eight carbon atoms because these molecules are unstable and tend to break down. Monosaccharides often attach themselves to one another to form larger, more complex molecules such as disaccharides and polysaccharides. Monosaccharides have different chemical properties depending on their molecular structure.

Brief History

Monosaccharides, disaccharides, and polysaccharides are the three different types of carbohydrates. Monosaccharides belong to one of two classes: ketoses and aldoses. The means of determining whether a monosaccharide is a ketose or aldose is to assess whether the monosaccharide’s functional group (each monosaccharide has only one functional group) is an aldehyde or ketone. An aldehyde is an organic compound that contains a formyl group, while a ketone is another type of carbonyl group, one without a hydrogen atom attached and available for being oxidized.

One of the first scientists to study monosaccharides in detail was Emil Fischer, who was active during the latter part of the nineteenth century. Fischer developed a special notation to describe the structure and composition of monosaccharides, known as Fischer projection, and this notation is still used for this purpose. In Fischer projections, the ketone or aldehyde appears at the top of a vertical structure, with the other atoms in the structure appearing below it

Monosaccharides are found in most living things. In animals, they appear in the bloodstream as they are transported from one part of the body to another, allowing the organism to transfer energy (stored in the monosaccharide’s chemical bonds) from one location to another. When they reach their destination they are broken down, and the chemical energy stored in their molecular bonds is released so that it can be used by the organism’s cells. Monosaccharides can be thought of as high capacity batteries because they are able to store a large amount of potential energy inside themselves—much more energy than other substances. Because energy is required in order to sustain life, organisms able to assess sources of monosaccharides will have access to greater amounts of energy in the form of food, and thus be better equipped to survive. Human beings may have evolved in such a way as to be attracted to the taste of monosaccharides, as an incentive to acquire and consume them, because doing so provides more food energy and thus a higher chance of survival.

Overview

Glucose is the monosaccharide most people are familiar with, in part because it is so common. Its ubiquity is due to the fact that it is produced by plants through photosynthesis. Plants use energy from the sun to combine together water (which consists of hydrogen and oxygen) and carbon dioxide in the air, and the result is the carbohydrate glucose, made of carbon, hydrogen, and oxygen. This glucose is then incorporated into the plant and used by the plant to store and carry energy in the chemical bonds. With some plants, the energy stored in the glucose does not remain in the plant, but is consumed by other organisms so that they can acquire the energy it contains. Glucose is a primary energy source for organisms as simple as bacteria and as complex as human beings.

In human beings, the starches that contain glucose are made available as energy through the operation of a complex digestive process that involves many different organs. When glucose-bearing starch (a polysaccharide) is ingested, the first step in the process is for enzymes in the saliva to begin breaking down the starch. This prepares the starch for the next stage, which occurs in the stomach and intestines. There, enzymes released by the pancreas further break down the starches into disaccharides. When these disaccharides reach the walls of the intestine, disaccharidase enzymes there break the disaccharides down into monosaccharides. These monosaccharides then pass through the intestinal wall via capillaries and reach the bloodstream. The monosaccharides are carried in the blood to the liver, where they are converted to glucose and then sent throughout the body as a means of carrying stored energy to cells.

Monosaccharides appear in one form or another in almost every form of food. The monosaccharide fructose, for example, is also known as fruit sugar because it is contained in many fruits such as watermelon, mangoes, apples, and pears. Fructose is present in many sweeteners used in cooking and baking, such as honey and agave syrup. The monosaccharide glucose is also a sweetener, known as dextrose, used in packaged food and in medicine. Glucose appears naturally in foods such as blueberries, cantaloupe, and papaya.

People with certain dietary needs or digestive issues must sometimes pay strict attention to whether they are consuming monosaccharides, disaccharides, or polysaccharides. Those who follow the specific carbohydrate diet (SCD) are restricted from eating polysaccharides and disaccharides, but may freely consume monosaccharides. This means that they must avoid grains and vegetables with high starch content, and instead choose foods with lower amounts of starch, such honey and some vegetables. As is often the case with dietary restrictions, there is an absence of agreement on the exact nature of the benefits that can be expected by following such a strict regimen; some people insist that following SCD is completely ineffective, while others insist that it has permitted them to regain a quality of life that they previously had thought unattainable due to their medical condition.

Bibliography

Benkeblia, Noureddine. Polysaccharides: Natural Fibers in Food and Nutrition. Boca Raton: CRC, Taylor, 2014. Print.

Fujii, M., et al. "Monosaccharide Composition of the Outer Membrane Lipopolysaccharide and O-Chain from the Freshwater Cyanobacterium Microcystis Aeruginosa NIES-87." Journal of Applied Microbiology 113.4 (2012): 896–903. MEDLINE with Full Text. Web. 13 July 2015.

Grace, Olwen M., et al. "Monosaccharide Analysis of Succulent Leaf Tissue in Aloe." Phytochemistry 93 (2013): 79–87. MEDLINE with Full Text. Web. 13 July 2015.

Jordan, David S., James M. Daubenspeck, and Kevin Dybvig. "Rhamnose Biosynthesis in Mycoplasmas Requires Precursor Glycans Larger Than Monosaccharide." Molecular Microbiology 89.5 (2013): 918–928. MEDLINE with Full Text. Web. 13 July 2015.

Lütteke, Thomas, and Martin Frank. Glycoinformatics. New York: Humana, 2015. Print.

Reddy, Rachamalla Maheedhar, Akshay Srivastava, and Ashok Kumar. "Monosaccharide-Responsive Phenylboronate-Polyol Cell Scaffolds for Cell Sheet and Tissue Engineering Applications." Plos One 8.10 (2013): e77861. MEDLINE with Full Text. Web. 13 July 2015.

Restaino, Odile Francesca, et al. "Monosaccharide Precursors for Boosting Chondroitin-Like Capsular Polysaccharide Production." Applied Microbiology and Biotechnology 97.4 (2013): 1699–1709. MEDLINE with Full Text. Web. 13 July 2015.

Sompong, Weerachat, et al. "A Comparative Study of Ferulic Acid on Different Monosaccharide-Mediated Protein Glycation and Oxidative Damage in Bovine Serum Albumin." Molecules 18.11 (2013): 13886–13903. MEDLINE with Full Text. Web. 13 July 2015.