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LECTERE 3

LECTERE 3. THEME: Carbohydrates: classification, chemical and physical properties. Structure of monosaccharides, olihosaccharides, homo- and heteropolisaccharides. Lecturer: Dmukhalska Yevheniya. B. Plan . Carbohydrates. Biological role of carbohydrates in an organism.

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LECTERE 3

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  1. LECTERE 3 THEME: Carbohydrates: classification, chemical and physical properties. Structure of monosaccharides, olihosaccharides, homo- and heteropolisaccharides. Lecturer: Dmukhalska Yevheniya. B.

  2. Plan • Carbohydrates. • Biological role of carbohydrates in an organism. • Classification of carbohydrates. • Structure and stereoisomerism, chemical properties of monosaccharides. • Olygosaccharides. Structure and biological role. • Homopolysaccharides. Structure and biological role. • Heteropolysacchrides. Structure and biological role.

  3. Carbohydrates are polyhydroxy aldehydes such as D-glucose, polyhydroxy ketones such as D-fructose, and compounds such as sucrose that can be hydrolyzed to polyhydroxy aldehydes or polyhydroxy ketones.

  4. Biological role of carbohydrates • Carbohydrate oxidation provides energy. • Carbohydrate storage, in the form of glycogen, provides а short- term energy reserve. • Carbohydrates supply carbon atoms for the synthesis of other biochemical substances (proteins, lipids, and nucleic acids). • Carbohydrates form part of the structural framework of DNA and RNA molecules. • Carbohydrate "markers" on cell surfaces play key roles in cell -cell recognition processes.

  5. Classification • Monosaccharides are carbohydrates that contain a single polyhydroxy aldehyde or polyhydroxy ketone unit. Glucose, fructose. • Oligosaccharides are carbohydrates that contain from two to ten monosaccharide units. Lactose, sucrose. • Polysaccharides are carbohydrates made up of many monosaccharide units. Cellulose, starch.

  6. Classification of monosaccharides. • Monosaccharides are classified by the basis of type of carbonyl group, which are present in molecule: • Aldoses are monosaccharides that contain an aldehyde group. • Ketoses are monosaccharides that contain а ketone group. • Monosaccharides are often classified by number of carbon atoms. • А six-carbon monosaccharide is an hexose; • A five-carbon monosaccharide – pentose; • A four-carbon monosaccharide – tertrose.

  7. The smallest aldose, and the only one whose name does not end in “ose,” is glyceraldehyde, an aldotriose.

  8. Any organic molecule containing а single carbon atom with four different groups attached to it exhibits chirality. • А chiral center is an atom in а molecule that has four different groups tetrahedrally bonded to it. It is asymmetric atom. • Enantiomers are stereoisomers whose molecules are nonsuperimposable mirror images of each other.

  9. Properties of enantiomers • Enantiomers are said to be optically active because of the way they interact with plane-polarized light. An optically active compound is а compound that rotates the plane of polarized light.

  10. An enantiomer that rotates plane-polarized light to the right is said to be dextrorotatory (the Latin dexter means "right"). An enantiomer that rotates plane-polarized light to the left is said to be levorotatory (the Latin laevus means "left"). • А plus or minus sign inside parentheses is used to denote the direction of rotation of plane-polarized light by а chiral compound. The notation (+) means rotation to the right (clockwise), and (-) means rotation to the left (counterclockwise). Thus the dextrorotstory enantiomer of glucose is (+)-glucose. • An equimolar mixture of two enantiomers is called а racemic mixture, or а racemate. Since а racemic mixture contains equal numbers of dextrorotating and levorotating molecules, the net optical rotation is zero. А racemic mixture is often specified by prefixing the name of the compound with the symbol ( )

  11. Stereoisomerism results either from the presence of а chrial center or from structural rigidity caused by restricted rotation about chemical bonds. • Enantiomers: Stereoisomers that are nonsuperimposable mirror images of each other. Enantiomers rotate plane-polarized light in different directions. (+) Enantiomers are dextrorotatory (clockwise), and (-) enantiomers are levorotatory (counterclockwise). • Diastereomers - stereoisomers that are not mirror images of each other. • Epimers are called such diastereomers that differ in configuration at only one asymmetric carbon.

  12. Configurations of Aldoses

  13. Configurations of Ketoses

  14. Biologically important monosaccharides. D-Galactose D-Glucose D-Fructose D-Ribose 2-Deoxy-D-ribose

  15. Haworth Projection Formulas

  16. The D or L form of а monosaccharide is determined by the position of the terminal СН2ОН group on the highest-numbered ring carbon atom. In the D form, this group is positioned above the ring. In the L form, which is not usually encountered in biological systems, the terminal CH2OH group is positioned below the ring.

  17. or  configuration is determined by the position of the -ОН group on carbon-1. In а  configuration OH group is positioned above the ring; in an  configuration OH group is positioned below the ring. • -D-Monosaccharide-D-Monosaccharide

  18. Haworth projection and Fischer projection -form-form

  19. Mutarotation. • - and -forms of monosaccharides are readily interconverted when dissolved in water. • This spontaneous process, called mutarotation. • A slow change in optical rotation to an equilibrium value is known as mutarotation.

  20. Oxidation • Weak oxidizing agents, such as Tollens, Fehling's, and Benedict's solutions, oxidize the carbonyl (aldehyde) group end of а monosaccharide to give a glyconic acid. Oxidation of glucose produces gluconic acid.

  21. Strong oxidizing agents can oxidize both ends of а monosaccharide at the same time to produce а dicarboxylic acid - aldaric acids. For glucose, such an oxidation produces glucaric acid.

  22. In biological systems enzymes can oxidize the primary alcohol end of an aldose, to produce а gylcuronic acid. For glucose, such an oxidation produces D-glucuronic acid.

  23. Reduction. • Aldoses and ketoses, the product of the reduction is the corresponding polyhydroxy alcohol (sugar alcohol). The reduction D-glucose gives D-glucitol (D-sorbitol).

  24. Osazone Formation

  25. Glycoside Formation. Methyl--D-glucoside Methyl--D-glucoside

  26. Acylation and Alkylation of Monosaccharides

  27. Phosphate ester formation -D-Glucose-1-phosphate -D-Glucose-6-phosphate

  28. Amino Sugar -D-Glucosamine -D-Glalactosamine N-acety1-D-glucosanune

  29. Isomerization

  30. Oligosaccharides • Upon hydrolysis, а disaccharide produces two monosaccharides, а trisaccharide three monosaccharides, а hexasaccharide six monosaccharides, and so on. • Disaccharides are carbohydrates composed of two monosaccharide units covalently bonded to each other. • The common disaccharides have the general formula C12H22O11. • Disaccharides are sweet-testing crystalline, water-soluble substances, easily hydrolysed by enzymes and dilute mineral acids.

  31. Biological role • Within the human body, oligosaccharides are often found associated with proteins and lipids in complexes that have both structural and regulatory functions. • Free oligosaccharides, other than disaccharides, are seldom encountered in biological systems. • Complete hydrolysis of an oligosaccharide produces monosaccharides.

  32. Disaccharides may be of two types, namely non-reducing and reducing depending on the fact that С1 of one hexose is linked to the carbonyl carbon at in or any other carbon atom of other hexose.

  33. Nоn-reducing disaccharides. In these disaccharides the two hexose units are linked together through their reducing groups which is С, in aldoses and С, in ketoses. Important example of non-reducing disaccharides is sucrose. Reducing disaccharides. In these disaccharides, one hexose unit is linked through its reducing carbon to the non-reducing carbon (C4 or С6). Maltose and lactose – reducing disaccharides.

  34. Disaccharides formation Monosaccharide + monosaccharide = disaccharide + Н2O (Functioning as а (Functioning as (Glycoside) hemiacetal or an alcohol) а hemiketal)

  35. Disaccharide

  36. Maltose • Malt sugar, is produced whenever the polysaccharide starch breaks down, as happens in plants when seeds germinate and in human beings during starch digestion. • Structurally, maltose is made up of two D-glucose units, one of which must be -D-glucose. • -D-Glucose -D-Glucose -(1-4)-linkage • The glycosidic linkage between the two glucose units is called an (1 - 4) linkage. Maltose is а reducing sugar.

  37. Lactose is made up of а -D-galactose unit and а D-glucose unit joined by -(1 - 4) glycosidic linkage. • -D-galactose -D-Glucose (1 - 4)-linkage • Lactose is а reducing sugar

  38. The two monosaccharide units present in -D-sucrose molecule are -D-glucose and -D-fructose. It is instead an ,(1-2) glycosidic linkage. Sucrose is а non-reducing sugar

  39. Sucrose is dextrorotatcry. Sucrose hydrolysis (digestion) produces an equimolar mixture of glucose and fructose. Now since fructose is more strongly laevorotatory than the dextrorotatory property of glucose, the mixture (product) after hydrolysis will be laevorotatory. dextrorotatcry laevorotatory This reaction is also as inversion of sugar because the dextrorotatory case sugar is converted into laevorotatory product due to hydrolysis. The mixture of glucose and fructose is called invert sugar..

  40. А polysaccharide (glucans) • А polysaccharide contains many monosaccharide units bonded to each other by glycosidic linkages. • Polysaccharides may be divided into two classes: homopolysaccharides, which are composed of one type of monosaccharide units, and heteropolysaccharides, which contain two or more different types of monosaccharide units. • Homoglycans (glucans or glucosans): starch, glycogen and cellulose. They are made of only glucose. • Heteropolysaccharides (Mucopolysaccharides): hyaluronic acid and chondroitin sulphates. They are made up of different monosaccharide units.

  41. Cellulose.Structurally, cellulose is а linear (unbranched) D-glucose polymer in which the glucose units are linked by (1-4) glycosidic bonds.

  42. Starch is а polysaccharide containing only glucose units. Two different polyglucose polysaccharides can be isolated from most starches: amylose (15-20%) and amylopectin (80-85%) • Amylose: Up to 1000 glucose units; no branching; molecular mass is 50,000 amu or more • Amylopectin: Up to 100,000 glucose units; branch points every 24-30 glucose units; molecular mass is 300,000 or more for • Glycogen: Glycogen is about three times more highly branched than amylopectin, and it is much larger, with а molar mass of up to 3,000,000 amu.Up to 1,000,000 glucose units; branch points every 8-12 glucose units. • Liver cells and muscle cells are the storage sites for glycogen in humans.

  43. Amylose Amylopectin

  44. (1,4)-O--D-Glucopyranosyluronic acid-(1,3)-2-acetamindo-2-deoxy--D-glucopyranose. • Hyaluronic acid:It consists N- acetylglucosamine (NAG) and glucuronic acid linked according to the principle discussed above. Note also, in this structure, the alternating pattern of glycosidic bond types, (1 - 3) and  (1-4). It is а highly viscous substance and has а molecular weight in several 100 millions. • Hyaluronic acid is а principal component of the ground substance of connective tissue. Among other places it is found in skin, synovial fluid, vitreous hemour of the eye, and umbilical cord. Synovial fluid which contains about 0.02 – 0.05% of hyaluronate.

  45. Chondroitinsulphate. It has similar structure as hyaluronic acid with the difference that the N-acetyl glucosamine unit of the latter is replaced by N-acetyl galactosamine 6 sulphate unit. The two other chondriotin sulphates are А and В; the type А nas sulphate group in position 4 while the type В has L-iduronate (а stereoisomer оf D-glucuronic acid) in place of D-glucuronic acid. Chondroitin sulphates are found in cartilage, bone, heart valves, tendons and cornea. (1,4)-O--D-Glucopyranosyluronic acid-(1,3)-2-acetamindo-2-deoxy-6-O-sulfo--D-galactopyranose

  46. Dermatansulfate. Varying amounts of D-glucuronic acid may be present. Concentration increases during aging process. (1,4)-O--L-Idopyranosyluronic acid-(1,3)-2-acetamindo-2-deoxy-4-O-sulfo--D-galactopyranose

  47. Heparin. It is naturally occurring anticoagulant found mainly in the liver, and also in lung, spleen, kidney and iatestinal mucosa. It prevents blood clotting by inhibiting the prothrombin-thrombin conversion and thus eliminating the thrombin effect on fibrinogen. This polysaccharide is composed of glucosamiae-N-sulphate aad sulphate ester of glucuronic acid linked via 1  4 - 1 4 linkages (difference from hyaluronic acid and chondroitin sulphates). (1,4)-O--D-Glucopyranosyluronic acid-2-sulfo-(1,4)-2-sulfamindo-2-deoxy-6-O-sulfo--D-glucopyranose

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