Tiêu đề 9. CARBOHYDRATES AND RELATED PRODUCTS.pdf ✅

PHARMD GURU Page 1 INTRODUCTION: They are organic compounds found in the major part of fruits, vegetables, legumes and cereal grains. They carry out many functions in all living organisms. These are large biomolecules, consisting of carbon (C), hydrogen (H) and oxygen (O) in their basic structure. Chemically, they are simple organic compounds that are aldehydes or ketones with many hydroxyl groups added on each carbon atom which are not part of either of these both functional groups. The basic formula is Cm(H2O)n where “m” is different from “n”. The hydrogen and oxygen ratio is 2:1, hence they are known as hydrates of carbon. So, carbohydrate is defined as polyhydroxy aldehydes or polyhydroxy ketones which give these on hydrolysis and contains at least one chiral carbon atom. Carbohydrates are produced in green plants by photosynthesis and serve as a major source of energy in animals. They also serve as structural components, such as cellulose in plants and chitin in some animals. CLASSIFICATION: Carbohydrates are of three types namely simple sugar, polysaccharides and oligosaccharides (Fig. 5.8). The simplest carbohydrates are the three-carbon sugars, i.e. monosaccharides, and further cannot be hydrolysed to simple sugars. CARBOHYDRATES AND RELATED PRODUCTS
PHARMD GURU Page 2 Depending on the number of carbon atoms, monosaccharides are further classified into following:  Bioses are two-carbon compounds, but do not occur in free form in the nature.  Trioses are three-carbon compounds. They are in the form of phosphoric esters. Example: Glyceraldehyde.  Tetroses are four-carbon compounds. Examples: Erythrose, Threose.  Pentoses are five-carbon compounds and occur in plants. They are the products of polysaccharides such as hemicelluloses, mucilage etc. Examples: Ribose, Arabinose, Xylose etc.  Hexoses are six-carbon molecules and are abundantly available. On hydrolysis they produce starch and inulin. Examples: Glucose, Fructose etc. MONOSACCHARIDES:  Monosaccharides are classified according to three different characteristics: the placement of carbonyl group, the number of carbon atoms they contain, and their chiral handedness.  If the carbonyl group is an aldehyde, the monosaccharide is an aldose, and if the carbonyl group is a ketone, the monosaccharide is a ketose.  Aldose or aldo sugar containing compounds are glucose, galactose, ribose etc., whereas ketose or keto sugar containing compound is fructose.  Depending on the chemical nature of the sugar, they are also classified as reducing and non-reducing sugars. REDUCING SUGAR: Contain a hemiacetal or hemiketal group. Sugars include glucose, galactose, fructose, maltose, lactose. NON-REDUCING SUGAR: Hemiacetal groups are absent. Sucrose and all polysaccharides are present in this group. Heptoses contain seven carbon atoms and so on. Disaccharides are the compounds in which two monosaccharides are joined together and these are the simplest polysaccharides. Examples: Sucrose, lactose etc. Sucrose = Glucose and Fructose; Lactose = Galactose and Glucose; Maltose = Glucose and Glucose.
PHARMD GURU Page 3 TRISACCHARIDES: Trisaccharides are oligosaccharides composed of three monosaccharides with two glycosidic bonds connecting in between them. Examples: Raffinose (Glucose + Fructose + Galactose). POLYSACCHARIDES: Polysaccharides are polymeric carbohydrates that are composed of long or branched chains of monosaccharide units bounded together by glycosidic bonds. They are of two types viz. Structural polysaccharides and Digestible polysaccharides. Former one are digestible by herbivorous species — cellulose, lignin, dextrans, mannans, inulin, pentosans, pectic acids, algic acids, agar and chitin. Later one is starch.
PHARMD GURU Page 4 OLIGOSACCHARIDES: Oligosaccharides are saccharide polymers containing a small number of simple sugars. Some examples are fructo-oligosaccharides (FOS), which are found in many vegetables. FUNCTION: 1) They are used for energy storage and production. Starch and glycogen, respectively in plants and animals, are stored as carbohydrates from which glucose can be mobilized for energy production. 2) They exert a protein-saving action. 3) The presence of carbohydrates is necessary for the normal lipid metabolism. 4) Glucose is indispensable for the maintenance of the integrity of nervous tissue and red blood cells. 5) Two sugars, ribose and deoxyribose, are part of the bearing structure, respectively of the RNA and DNA and present in the nucleotide structure. 6) They take part in detoxifying processes. For example, at hepatic level glucuronic acid, synthesized from glucose, combines with endogenous substances, as hormones, bilirubin etc. 7) Carbohydrates are also found linked to many proteins and lipids. Within cells they act as signals that determine the metabolic fate or intracellular localization of the molecules which are bound. 8) Two homopolysaccharides, cellulose and chitin, serve as structural elements. 9) The cellulose in plants is used to manufacture paper, wood for construction, and fabrics. CHEMICAL TESTS: MOLISCH TEST:  Molisch reagent is mixed with a dilute solution of carbohydrate.  The test reagent dehydrates pentoses to form furfural (top reaction) and dehydrates hexoses to form 5-hydroxymethyl furfural (bottom reaction).  The furfurals further react with alpha-naphthol present in the test reagent to produce a purple product.  Pentoses and hexoses form five-member oxygen containing rings on dehydration.