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Similar a Carbohydrates: Definition, Classification and Biomedical Importance
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Carbohydrates: Definition, Classification and Biomedical Importance
- 2. • Definition: Carbohydrates are defined chemically as aldehyde or ketone derivatives of the higher polyhydric alcohols, or compounds which yield these derivatives on hydrolysis.
- 3. Biomedical Importance • Chief source of energy. • Most abundant dietary source of energy. Brain cells and RBCs are almost wholly dependent on carbohydrates as the energy source. • Participate in the structure of cell membrane & cellular functions (cell growth, adhesion and fertilization). • Constituents of compound lipids and conjugated proteins. • Degradation products act as “promoters” or ‘catalysts’. • Lactose principal sugar of milk—in lactating mammary gland.
- 4. • Constituents of mucopolysaccharides which form the ground substance of connective tissues. • Inherited deficiency of certain enzymes in metabolic pathways of different carbohydrates can cause diseases, e.g. galactosemia, glycogen storage diseases (GSDs), lactose intolerance, etc. • Derangement of glucose metabolism is seen in diabete smellitus. • Certain carbohydrate derivatives are used as drugs like cardiac glycosides/antibiotics.
- 5. • The Glycemic Index (GI) is a relative ranking of carbohydrate in foods according to how they affect blood glucose levels. Carbohydrates with a low GI value (55 or less) are more slowly digested, absorbed and metabolised and cause a lower and slower rise in blood glucose and, therefore usually, insulin levels. High GI value = more than 70.
- 6. 1 •Monosaccharide 2 •Oligosaccharides 3 •Polysaccharides Carbohydrates are divided into three major groups Classification
- 8. Monosaccharides • Also called ‘simple’ sugars are those which cannot be hydrolysed further into simpler forms. • General formula : Cn(H2O)n They can be subdivided further: (a) Depending upon the number of carbon atoms they possess, as trioses, tetroses, pentoses, hexoses (b) Depending upon whether aldehyde (– CHO) or ketone (– CO) groups are present as aldoses or ketoses
- 10. Trioses • Both D-glyceraldehyde and dihydroxyacetone occur in the form of phosphate esters, as intermediates in glycolysis. They are also the precursors of glycerol, which the organism synthesises and incorporates into various types of lipids. Tetroses • Erythrose-4-P occurs as an intermediate in hexosemonophosphate shunt which is an alternative pathway for glucose oxidation.
- 11. Pentoses • D-ribose is a constituent of nucleic acid RNA; also as a constituent of certain coenzymes, e.g. FAD, NAD,coenzyme A. • D-2-deoxyribose is a constituent of DNA. • Pentosuria is an inborn error of metabolism which is characterized by the excretion of 1 to 4 g of the pentose L-xylulose in the urine per day. • Pentosuria is the result of a defect in the glucuronic acid oxidation pathway. In this route of carbohydrate metabolism the carboxyl carbon atom of D-glucuronic acid is removed in a series of reactions, giving rise to the pentose L-xylulose.
- 12. Hexoses Glucose • It is the chief physiological sugar present in normal blood. • All tissues utilise glucose for energy. Erythrocytes and Brain cells utilise glucose solely for energy purposes. • Stored as glycogen in liver and muscles mainly.
- 13. Galactose • Occurs as a constituent of milk sugar lactose and also in tissues as a constituent of galactolipid and glycoproteins. • It is an epimer of glucose and differs in orientation of H and OH on carbon-4. • It is less sweet than glucose and less soluble in water. • Galactose is metabolized by conversion initially to glucose 1-phosphate (G1P), which can then be converted either to G6P or to glycogen • It is dextrorotatory in nature.
- 14. Fructose • It is a ketohexose and commonly called as fruit sugar, as it occurs free in fruits. • Pure fructose is much sweeter than other types of sugar. • Seminal fluid is rich in fructose and sperms utilise fructose for energy. • Crystalline fructose is used in enhancing the taste in food industries. • Fructose does not acutely raise blood glucose. As such, fructose has a lower glycemic index than do starch-based foods.
- 15. D-mannose • It does not occur free in nature but is widely distributed in combination as the polysaccharide mannan, e.g. in ivory nut. • In the body, it is found as a constituent of glycoproteins. Sedoheptulose • It is a ketoheptose found in plants of the sedum family. Its phosphate is important as an intermediate in the HMP-shunt and has been identified as a product of photosynthesis
- 16. Oligosaccharide • Oligosaccharides(Greek: oligo-few) contain 2- 1O monosaccharide molecules joined by glycosidic bond.
- 17. DISACCHARIDES • Three most common disaccharides of biological importance are: Maltose, Lactose and Sucrose. • Their general molecular formula is C12H22O11 and they are hydrolysed by hot acids or corresponding enzymes as follows: C12H22O11 + H2O → C6H12O6 + C6H12O6
- 18. Maltose • Maltose or malt sugar is an intermediary in acid hydrolysis of starch and can also be obtained by enzyme hydrolysis of starch. • In the body, dietary starch digestion by Amylase in gut yields maltose, which requires a specific enzyme maltase to form glucose.
- 19. Lactose • Lactose is milk sugar and found in appreciable quantities in milk . • It is not very soluble and is not so sweet. • On hydrolysis it yields one molecule of D-Glucose and one molecule of D-Galactose.
- 20. Sucrose • Ordinary table sugar is sucrose. It is also called as ‘Cane sugar’, as it can be obtained from sugarcane. • Also obtained from sugar beet, and sugar maple. Also occurs free in most fruits and vegetables, e.g. pineapples,and carrots. It is very soluble and very sweet and on hydrolysis yields one molecule of D- Glucose and one molecule of D-Fructose.
- 21. Sucrose is dextrorotatory (+62.5°) but its hydrolytic products are laevorotatory because fructose has a greater laevorotation than the dextrorotation of glucose. As the hydrolytic products invert the rotation, the resulting mixtures of glucose and fructose (hydrolytic products) is called as Invert Sugar and the process is called as Inversion.
- 22. POLYSACCHARIDES • Polysaccharides are more complex substances. Some are polymers of a single monosaccharide and are termed as Homopolysaccharides (Homoglycans), e.g.starch, glycogen. • Heteropolysaccharides (heteroglycans) contain two or more different monosaccharide units. Eg: Hyaluronic Acid, Heparin
- 23. HOMOPOLYSACCHARIDES (HOMOGLYCANS) Starch • Starch is a polymer of glucose, and occurs in many plants as storage foods. It may be found in the leaves, and stem, as well as in roots, fruits and seeds where it is usually present in greater concentration.
- 24. Glycogen • Glycogen is the reserve carbohydrate of the animal, hence it is called as animal starch. • It has been shown to be present in plants which have no chlorophyll systems, e.g. in fungi and yeasts. It is also found in large amounts in oysters and other shell fish. In higher animals, it is deposited in the liver and muscle as storage material which are readily available as immediate source of energy.
- 25. Cellulose • Cellulose is a polymer of glucose. It is not hydrolyzed readily by dilute acids, but heating with fairly high concentrations of acids yields, the disaccharide Cellobiose and D-Glucose. • Cellobiose is made up of two molecules of D- Glucose linked together by β-Glucosidic linkage between C1 and C4 of adjacent glucose units. Agar • It is a homopolysaccharide. Made up of repeated units of galactose which is sulphated. Present in seaweed. It is obtained from them
- 27. HETEROPOLYSACCHARIDES/ MUCOPOLYSACCHARIDES (MPS) • In general, heteropolysaccharides contain two or more different monosaccharide units. • They are long chains of sugar molecules that are found throughout the body, often in mucus and in fluid around the joints.
- 28. Hyaluronic Acid • A sulphate free mucopolysaccharide. • It is composed of repeating units of N-acetyl glucosamine and D-Glucuronic acid.
- 29. Heparin • It is also called α-Heparin. It is an anticoagulant present in liver and it is produced mainly by mast cells of liver (Originally isolated from liver). • In addition, it is also found in lungs, thymus, spleen, walls of large arteries, skin and in small quantities in blood. • It is a polymer of repeating disaccharide units of D-Glucosamine and L-Iduronic acid.
- 30. Chondroitin Sulphates • They are principal MPS in the ground substance of mammalian tissues and cartilage. They occur in combination with proteins and are called as Chondroproteins. • Four chondroitin sulphates have been isolated so far. They are named as chondroitin SO4 A, B, C and D.
- 32. Isomerism • Isomerism is the Phenomenon in Which More than One Compounds have the Same Chemical Formula but Different Structures.
- 33. Structural Isomerism • Structural Isomers have the same molecular formula but different arrangements of atoms. • There are three types of structural isomers: chain isomers, functional group isomers and positional isomers. • Eg : Aldose-Ketose Isomerism Glucose and Fructose are isomers of each other. Molecular Formula: C6H12O6
- 35. Stereoisomerism • Stereoisomers are molecules that share the same molecular formula and arrangement of atoms, differ from one another in 3-dimensional space. • Geometric isomers (called cis/trans isomers) can arise when a double bond or ring is present in a molecule. • Chiral carbon is the carbon atom about which all the 4 groups are different . • D and L enantiomers refer to the configurational stereochemistry of the molecule. L isomers have the hydroxyl group attached to the left side of the asymmetric carbon furthest from the carbonyl, while D isomers have the hydroxyl group on the right side
- 36. D & L -- Isomerism
- 38. Optical isomerism • Optical isomers are named like this because of their effect on plane polarized light. • Optical activity describes the phenomenon by which chiral molecules are observed to rotate polarized light in either a clockwise (Right side) or Anticlockwise (Lest side) direction. • Right = dextrorotatory (+) (d) • Left = levorotatory (-) (l) • A racemic mixture is a 50:50 mix of two enantiomers. No matter how many molecules are in a mixture, it is racemic if there are equal numbers of the two enantiomers.
- 40. Epimerism • Those stereoisomers which are differing in its configuration at only one chiral carbon atom are called as Epimers. • For example, glucose and galactose are Epimers of each other. • They differ in only in the position of hydroxyl group at C4 (chiral carbon atom).
- 42. Anomerism • Anomers are cyclic monosaccharides or glycosides that are epimers, differing from each other in the configuration of C-1 if they are aldoses or in the configuration at C-2 if they are ketoses. • Eg: α-D-Glucopyranose and β-D-glucopyranose are anomers.
- 45. Benedict’s test • The principle of Benedict's test is that when reducing sugars are heated in the presence of an alkali(pH 10.6), they get converted to powerful reducing compounds known as enediols. • Enediols reduce the cupric ions (Cu2+) present in the Benedict's reagent to cuprous ions (Cu+) which get precipitated as insoluble red copper oxide. • Any sugar with free aldehyde/keto group will reduce the Benedict's reagent. Therefore, this is not specific for glucose.
- 47. Osazone Formation • All reducing sugars will form osazones with excess of phenyl hydrazine when kept at boiling temperature. • Glucose, fructose, galactose and mannose formed needle shape osazone. • Maltose formed sun flower shape osazone.
- 49. Molisch’s test • All carbohydrates when treated with conc. sulphuric acid undergo dehydration to give fufural compounds. These compounds condense with Alpha-napthol to form colored compounds. • Molish test is given by sugars with at least five carbons because it involves furfural derivatives, which are five carbon compounds.
- 51. Fehling’s test • Same principle as benedicts test • Fehling’s A contains 7% copper sulphate and Fehling’s B contains sodium potassium tartarate. • Fehling's test can be used as a generic test for monosaccharides. It will give a positive result for aldose monosaccharides (due to the oxidisable aldehyde group) but also for ketosemonosaccharides, as they are converted to aldoses by the base in the reagent, and then give a positive result.
- 53. Barfoed’s Test • This test is based on the same principle as Benedict’s test. • But, the test medium is acidic. • In acidic medium (pH 4.6) monosaccharides react faster than disaccharide. • Barfoed’s reagent contains copper acetate in glacial acetic acid.
- 55. Seliwanoff’s test • Seliwanoff’s test is a chemical test which distinguishes between aldose and ketose sugars. • Ketohexoses like fructose on treatment with HCl form 5-hydroxymethylfurfural, which on condensation with resorcinol gives a cherry red complex.
- 57. Iodine Test