Polysaccharides represent an almost unmanageably differentiated and large group of different carbohydrates consisting of a concatenation of more than 10 identical or even different monosaccharides glycosidically linked to each other. They are biopolymers that play a major role in human metabolism as energy stores, as structural elements in membranes, as components of proteins (proteoglycans), and for immunomodulation.
What are polysaccharides?
Polysaccharides, also known as glycans or polysaccharides, belong to the carbohydrate group of substances. Polysaccharides are formed by the concatenation of at least 10 monosaccharides that are linked together glycosidically. They can consist of linkages of up to several tens of thousands of monosaccharides, which also have lateral branching. Saccharides consisting of a glycosidic linkage of fewer than 10 monosaccharides are called di-, tri-, or oligosaccharides. The linked monosaccharides can consist of the same or different monosaccharides. Consequently, they are then homoglycans or heteroglycans. While saccharides up to the level of oligosaccharides taste sweet, polysaccharides are neutral in taste and hardly soluble in water. In principle, a distinction can be made between an O-glycosidic and an N-glycosidic bond. It is remarkable that this group of substances, which is so important for metabolism, is usually composed exclusively of the three elements carbon, hydrogen and oxygen. These are the three elements that are abundantly available almost everywhere in the Earth’s biosphere. In some cases, nitrogen (N), which is also available in unlimited quantities, also plays a role. Many polysaccharides can be described with the following chemical formula (Cx(H2Oy)n. Here, x usually takes the value 5 or 6 and y takes the value x minus 1.
Function, effect and tasks
The substance group of polysaccharides performs three important main functions in human metabolism (metabolism). They serve as energy stores in the form of glycogen, as substances that provide structure and strength, and they exert an influence on the immune system. Glycogen is a homoglycan composed of up to 50,000 glucose monomers in strong branching. It assumes the role of short- to medium-term energy storage. For longer-term energy storage, glycogen is introduced into fat metabolism and converted into body fat. During intense muscular activity or other energy requirements, the body can initially draw on glycogen stores because the individual glucose molecules can be released from glycogen with little effort. The plant counterpart to glycogen is starch (amylopectin and amylose). Polysaccharides play a special role as a component of the glycocalyx, the membrane that envelops human and animal cells as a protection against desiccation and phagocytosis, and as an intercellular means of communication. As a component of proteoglycans, which make up the bulk of the extracellular matrix, polysaccharides provide the necessary strength and cohesion of the various tissues. Heteroglycans also play an important role in cartilage formation in the form of glycosaminoglycans, which are composed of disaccharide units. This is hyaluronic acid, which has an enormous water-binding capacity as well as other special properties. Certain polysaccharides, which are mainly found in medicinal plants or fungi, are said to have an immunomodulating effect. This means that allergic reactions of the immune system or even autoimmune reactions are said to be improved by specific polysaccharides.
Formation, occurrence, properties, and optimal values
A mixture of monosaccharides, oligosaccharides, and polysaccharides is usually ingested with carbohydrate-containing foods. While monosaccharides are usually already converted in the mouth by the enzyme amylase into glucose, the form of sugar that can be utilized by the body, the higher-order sugars, oligo- and polysaccharides, must first be fractionated, which occurs mainly in the first section of the small intestine by means of specific sugar-degrading enzymes. Most of the enzymes are contributed to the small intestine by the pancreas.The “broken down” parts of the polysaccharides are absorbed by the intestinal mucosa of the small intestine and introduced into the portal vein, where they are transported to the liver for further processing. The glucose that is not immediately required as an energy source by muscles or, for example, the central nervous system, or for other purposes by the metabolic system, after being converted back into depot-ready glycogen, enters decentralized depots where it can be retrieved at short notice at any time. The process is very dynamic, since it also serves in part to regulate the glucose level in the blood, so that the specification of an optimal value does not seem reasonable.
Diseases and disorders
The most common inherited or acquired metabolic disease related to sugar metabolism is diabetes mellitus (diabetes). In this case, the body’s metabolism is unable to regulate glucose levels in the blood, and a persistent, elevated, glucose level tends to develop. In most cases, the pancreas is no longer able to produce enough insulin to break down the excess glucose, or insulin resistance sets in. This means that the blood glucose level does not respond or responds too little to insulin. In the case of diabetes, the consumption of digestible carbohydrates – including polysaccharides – must be well controlled and adjusted to the intended activity and the current blood glucose level. A common problem is lactose intolerance, which is caused by a genetic enzyme deficiency. Lactose (milk sugar) is broken down in the intestine to glucose and galactose. However, this requires the presence of the enzyme galactase. About 10 to 20 percent of Central Europeans suffer from a genetic deficiency of galactase. Consumption of products containing lactose causes digestive problems in those affected because fermentation processes occur in the intestine.
