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Carbohydrates
Most abundant organic molecules in nature. Carbohydrates are one of three macronutrients. They are primarily composed of elements carbon, hydrogen and oxygen. General formula C (^) x(H 2 O) y. Carbohydrates, also known as saccharides or carbs, provide energy for the body. Each gram of carbohydrates provides 4 calories. The body breaks carbohydrates down into glucose, which is the primary energy source for the brain and muscles. They serve as the storage form of energy. They participate in the structure of cell membrane and cellular functions.
They are structural components of many organisms which include cellulose of plants, exoskeleton of some insects. Carbohydrates are precursors for many organic compounds such as fats, amino acids. Classification : Based on the number of sugar units : Monosaccharides Oligosaccharides Polysaccharides Monosaccharides (simple sugars) : Simplest group of carbohydrates. They cannot be further hydrolysed. Monosaccharides are classified based on functional group : Aldoses & Ketoses.
on hydrolysis. Based on the number of monosaccharide units present, oligosaccharides are further subdivided into : Disaccharides – eg: sucrose (glucose + fructose), lactose (glucose + galactose), maltose (glucose + glucose) Trisaccharides – eg : Raffinose Tetrasaccharisdes - eg : stachyose Pentasaccharide – eg : verbacose Polysaccharides : Composed of more than 10 sugar units. Having high molecular weight. Tasteless and they can form colloids with water. Polysaccharides
Classified as, Homopolysaccharides : possess single type of monosaccharide. Eg : starch, glycogen. Hetero polysaccharides : possess 2 or more different monosaccharide units. Eg : Heparin, chodroitin sulphate. Monosaccharides Properties : They do not undergo Hydrolysis. They are soluble in water, they are sweet in taste. They’re reducing sugars (because of the presence of free -CHO or free -CO group) They exhibit stereoisomerism. Eg : glucose, fructose, mannose, galactose.
Due to the presence of the keto group, it results in the formation of intramolecular hemiketal form. In this arrangement, C5-OH combines with the ketonic group present in the second position. This results in the formation of furanose ring structures, α-D-fructofuranose and β-D-fructofuranose. Mannose : Mannose is a sugar monomer of the aldohexose series of carbohydrates. Glucose
Galactose is also found in complex carbohydrates and in carbohydrate- containing lipids called glycolipids, which occur in the brain and other nervous tissues of most animals.
Uses of Galactose : Galactose is a simple sugar that is essential for the body's metabolism and the delivery of energy. It is crucial during the early stages of human development. Galactose is beneficial for the digestive system, as it maintains healthy levels of intestinal bacteria. This improves food digestion and also strengthens the body's resistance to infections. It is used in clinical trials to study the treatment and diagnosis of Hepatitis C, Hepatic Cancer, Wilson's Disease, Diabetic Macular Oedema, and Focal Segmental Glomerulosclerosis, among others. It is also largely employed as a pathway to generate glucose fuel for the human body.
It is composed of two components : Amylose (α-amylose), a long unbranched straight-chain component. Made up of D-glucose units linked by α (1-4) glycosidic bond. Enzymatic hydrolysis of amylose by amylase gives maltose. Amylose is responsible for the blue colour formed by the reaction with iodine due to the incorporation of iodine into the helical structure of amylose. Amylose and Amlyopectin
Amylopectin (β-amylose), a branched chain polysaccharide. Made up of D- glucose units joined by α (1-4) and α (1-6) glycosidic bond. Branched chain polymer. On hydrolysis, yields isomaltose. Insoluble in cold water but soluble in hot water. Cellulose : The most abundant of all biomolecules in the biosphere. Cellulose occurs in the cell walls of plants. It is made up of β -D-glucose molecules linked together by β-1, 4-glycoside linkage. Thus, it resembles the structure with amylose except that the glucose units are linked together by β-1, 4-glycoside linkage. Insoluble in water but soluble in ammoniacal cupric hydroxide solution.
Cellulose is a relatively inert material and is completely degraded only under the most drastic conditions. Glycogen : It is the major reserve food in animals and is often called ‘animal starch’. Glycogen is stored in the liver and muscles of animals. Glycogen is a branched-chain polysaccharide and resembles amylopectin very much in structure, rather than amylose. But has more Glucose residues per molecule and about one-and-a- half times as many branching points. Also the chains are shorter (10–20 glucose units). More soluble in water than amylopectin. Hence, it readily forms suspension even in cold water.
It is a nonreducing sugar and gives red colour with Iodine. The red colour, however, disappears on boiling and reappears on cooling. On incomplete hydrolysis with α-1,4-glucanmaltohydrolase, glycogen yields maltose. However, the acids completely hydrolyze it into glucose. Heteropolysaccharides : Heteropolysaccharides are made up of more than one type of monosaccharide unit. Also called mucopolysaccharides or glycosaminoglycans. Composed not only of a mixture of simple sugars but also of derivatives of sugars such as amino sugars and uronic sugars. They are gelatinous in nature. Most of these act as structural support material for connective tissue or mucous substances of the body.
The high viscosity of the synovial fluid and its role as biological lubricant is largely due to the presence of its hyaluronic acid content. It is a straight-chain polymer of alternating units of D-glucuronic acid and N-acetyl- D-glucosamine (NAG) held together by β-1 → 3 glycosidic bond. Disaccharide units are joined by β-1 → 4 linkage. Hyaluronic acid, upon hydrolysis by hyaluronidase yields an equimolar mixture of D-glucuronic acid, D-glucosamine and acetic acid. Chondroitin sulfate : Derivatives of chondroitin Widely distributed and form major structural components of cartilage, tendons and bones. It is composed of repeating units of D-glucuronic acid and N-acetyl-D- galactosamine 4-sulfate joined by β(1-3) linkage.
The disaccharide units are linked by β(1-4) linkage. Heparin : Heparin acts as an anticoagulant. It prevents coagulation of blood by inhibiting the prothrombin - thrombin conversion. This eliminates the effect of thrombin on fibrinogen. It is present in liver, lung, arterial walls and, indeed, wherever mast cells are found, possibly for the purpose of neutralizing biogenic amines. (e.g. histamine). It is composed of alternating units of N-sulfo-D-glucosamine-6-sulfate and D- glucuronic-2-sulfate linked by α(1-4) linkage. Dermatan sulfate : It is found mainly in skin but also is in vessels, heart, lungs.
