Carbohydrates 1 Dr Vivek Joshi

Contents and Learning Objectives Introduction Functions General classification Various representation Monosaccharide structure and isomerism Disaccharides- Sucrose, Lactose & Maltose Polysaccharides- Starch, Glycogen Acidic Polysaccharides: biological importance 2

Introduction Proximate principle of the diet-Carbohydrate, Lipid, Protein Carbohydrate: ◦ Energy: 4 kcal/gm ◦ 60-70% of energy ◦ Preferred fuel ◦ Brain and RBC are wholly dependent on Glucose for their energy needs Lipid: ◦ Energy: 9 kcal/gm ◦ Concentrated fuel substance Protein: ◦ Tissue building material ◦ Many special functions- enzymes, antibodies, carrier molecules etc. 3

Functions of Carbohydrates Source and storage of energy In structure of connective tissue Synthesis of biologically important compounds like:  Ribose and Deoxyribose in Nucleic acid  Glycoprotein in Hormones, Blood group substances  Glycolipid in Nervous tissue  Proteoglycan in mucous secretion  Glucuronic acid in detoxification 4

Carbohydrates: Definition & Name “Polyhydroxylated aldehyde and ketone derivatives or compounds that gives these compounds on hydrolysis”  “ hydrate of carbon”  Empiric formula: C n (H 2 O) m  Saccharide: simpler members of carbohydrate family (saccharum=sugar, for sweet taste)  Suffix: ‘-ose’  Prefix: tri-, tetr-, pent-, hex- etc. indicates number of carbon atoms  Carbohydrates  Containing aldehyde group= aldoses  Containing ketone group= ketoses 5

Carbohydrates Classification Monosaccharide [One sugar unit-C n H 2n O n or C n (H 2 O) n ]  Triose (3C)  Tetrose (4C)  Pentose (5C)  Hexose (6C)  Heptose (7C) Disaccharide [Two sugar units-C n (H 2 O ) (n-1) ]  Sucrose (Glucose and Fructose)  Maltose (Glucose and Glucose)  Lactose (Glucose and Galactose) Oligosaccharide [3-10 sugar units]  Stacchyrose, Raffinose Polysaccharide [>10 sugar units]  Starch  Glycogen  Cellulose  Hyaluronic acid  Heparin 6

7 Aldoses: Monosaccharides

8 Ketoses: Monosaccharides

Various Representation Fischer Projection Formulas: ◦ A two dimensional representation showing the configuration of a stereocenter; ◦ Horizontal lines represent bonds projecting forward ◦ Vertical lines represent bonds projecting toward the back ◦ D and L varieties Cyclic Structure: ◦ Pyran: six membered ring ◦ Furan: five membered ring Haworth Projection: ◦ A flat ring as is viewed through its edge ◦ α and β varieties Conformational Representation: ◦ Chair 9

Monosaccharide Structure and Isomerism  Types of isomerism 1. Functional isomerism:  Aldose & Ketose 2. Stereoisomerism:  D and L 3. Anomerism:   and  4. Optical Isomerism:  d(+) and l(-) 5. Epimerism 10

1. Functional isomerism Exhibited by the monosaccharides having the same molecular formula but different functional groups Sugar with Aldehyde group- Aldose sugar Sugar with Keto group- Ketose sugar Monosaccharides are subclassified as: AldoseKetose Triose (3C)GlyceraldehydeDihdroxy acetone Tetrose (4C)Erythrose Erythrulose Pentose (5C)RiboseRibulose Hexose (6C)GlucoseFructose Heptose (7C)HeptoseSedoheptulose 11 Pentoses and hexoses are the most abundant monosaccharides in living cells

2. Streioisomerism Exhibited by the monosaccharides having the same molecular formula but differ in the arrangement of H and OH group around penultimate (last but one) carbon atom Asymmetric/Chiral carbon which is farthest from the functional group. D-sugar: -OH group on penultimate carbon atom is on the right L-sugar: -OH group on penultimate carbon atom is on the left 12

2. Streioisomerism (contd.) 13 D-Sugar: Naturally occurring Normally metabolized in the body. L-Sugar: Occur rarely Normally NOT metabolized in the body. Present in toxins, poison and Antibiotics

3. Anomerism  Exhibited by the sugars having the same molecular formula but differ in the arrangement of H and OH group around anomeric carbon atom  Anomeric carbon: due to cyclization, carbonyl carbon becomes new chiral center  [To remember, C bonded with functional group is anomeric carbon]  Anomeric carbon atom ◦ Involved in hemiacetal ring formation in Aldose ◦ Involved in hemiketal ring formation in Ketose ◦ C1 in Glucose ◦ C2 in Fructose   Anomer: -OH on the Right   Anomer :-OH on the Left 14 Note: Acetal is a molecule with two single bonded oxygens attached to the same carbon

3. Anomerism (contd.) Sugars that contain ≥ 4 carbons exist primarily in cyclic forms in aqueous solutions. Pyranose = 6-membered ring Furanose = 5-membered ring 15

3. Anomerism (contd.) 16 Glucose  C1 of Glucose forms hemiacetal ring with C5  Fischer projection  OH on the right at C1 -   OH on the left at C1-   Haworth projection  OH below the plane at C1 -   OH above the plane at C1 - 

3. Anomerism (contd.) 17 Fructose  C2 of Fructose forms hemiketal ring with C5  Fischer projection  OH on the right at C2 -   OH on the left at C2 -   Haworth projection  OH below the plane at C2 -   OH above the plane at C2 - 

3. Anomerism (contd.) 18 Glucose in solution - more than 99% is in the pyranose form β-D- Glucopyranose (62%) is the most predominant form of Glucose in blood.

3. Anomerism (contd.) 19 Fructose in solution – primarily in the furanose form

4. Optical Isomerism Exhibited by the sugars having the same molecular formula but differ in optical activity Beam of plane polarized light is made to pass through the solution of a compound ◦ dextrorotatory – d(+): Light rotated towards clockwise ◦ levorotatory – l(-): Light rotated towards anticlockwise Racemic mixture: Equimolar concentration of optical isomers ◦ No net optical rotation The specific rotation, [  ] D : Optical rotation expression under standard conditions ◦ The observed rotation when light of nanometer* (nm; 1 nm = m) wavelength is used with a sample pathlength l of 10 cm and a sample concentration C of 1 g /mL * Light of nm, sodium D line, is the orange light emitted from common sodium lamps 20

5. Epimerism  Exhibited by the sugars having the same molecular formula but differ in the arrangement of H and OH group around a single asymmetric carbon atom other than anomeric carbon atom  Glucose and Galactose are epimers at C4  Glucose and Mannose are epimers at C2  Epimerase enzyme: interconverts these epimers 21

Glycosidic bond  In Di, Oligo and Polysaccharides: Sugar units linked by glycosidic linkage  Glycosidic bond/linkage is formed by the condensation of the –OH group of the anomeric carbon of one sugar and an –OH group at any position on another sugar  Common Glycosidic linkage-Between C1 of the first sugar and the – OH at C4 of the second sugar (1 → 4 linkage) 22

Disaccharides A carbohydrate containing two monosaccharides units joined together by glycosidic bond ◦ Sucrose ◦ Lactose ◦ Maltose 23

Sucrose  Glucose + Fructose  Table sugar, Present in Fruits and Honey  Also from cane Sugar (sugarcane) and beet sugar   1,2-glycosidic bond  Non reducing sugar: because both anomeric carbons (C1 of glucose and C2 of fructose) are involved in glycosidic bond and not free to react 24

Lactose Galactose + Glucose Milk sugar  -1,4 glycosidic bond between C1 of Galactose and C4 of Glucose Reducing sugar: as the functional group (-CHO on C1) of 2 nd glucose is not involved in glycosidic bond and free to react, i.e. can be oxidized Also note  bonds in comparison to  bonds  bonds oriented above the plane of ring (as in anomers) 25

Maltose  Glucose + Glucose  Malt sugar   -1,4 glycosidic bond  Reducing sugar : as the functional group (-CHO on C1) of 2 nd glucose is not involved in glycosidic bond and free to react, i.e. can be oxidized  Also note  bonds below the plane of ring 26

Disaccharides: Must Remember! Common Name MonomersBondingReduction? SucroseTable sugarGlucose + Fructose  1,2-glycosidic bond Non-reducing LactoseMilk sugarGalactose + Glucose  -1,4- glycosidic bond Reducing MaltoseMalt sugarGlucose + Glucose  -1,4- glycosidic bond Reducing 27

Polysaccharides “a carbohydrate consisting of large numbers of monosaccharide units joined by glycosidic bonds” A. Starch B. Glycogen C. Cellulose 28

Starch Storage form of carbohydrate in plants Found in potatoes, corn, and cereal grains Polymer of only D-glucose Has two components 1. Amylose (20-25%): Continuous, un-branched chain of around 4,000 D-glucose units D-glucose residues - linked with  -1,4-glycosidic bonds 29

Starch (contd.) 2. Amylopectin (75-80%): ◦ Branched chains ◦ Around 10,000 Glucose residues united by  -1,4 linkages ◦ Branching point after every Glucose units with  -1,6- linkages 30

Glycogen  Storage form of carbohydrate in Animals  Stored in the liver and muscle  Polymer of around 10 6 glucose units  Glycosidic bonds are similar to amylopectin, but has more branches  Branches after every 8-10 glucose units  Total amount in human body = grams 31

All the bonds: Must Remember! Di/PolysaccharideBonds SucroseDi  1,2-glycosidic bond LactoseDi  -1,4 glycosidic bond MaltoseDi  -1,4 glycosidic bond Starch: (a) AmylosePoly only  -1,4-glycosidic bonds (b) Amylopectin  -1,4-glycosidic bonds with  -1,6- linkages at branches GlycogenPoly  -1,4-glycosidic bonds with  -1,6- linkages at branches CellulosePoly β -1, 4- glycosidic bonds 32

Acidic Polysaccharides “a group of polysaccharides that contain carboxyl groups and/or sulfuric ester groups, and play important roles in the structure and function of connective tissues”. Now being called Glycosaminoglycans There is no single general type of connective tissue. Rather, there are a large number of highly specialized forms, such as cartilage, bone, synovial fluid, skin, tendons, blood vessels, intervertebral disks, and cornea. Most connective tissues are made up of collagen, a structural protein, in combination with a variety of acidic polysaccharides. 33

Hyaluronic acid Simplest acid polysaccharide Contains from 300 to 100,000 repeating units. It is most abundant in embryonic tissues and in specialized connective tissues such as ◦ the synovial fluid, the lubricant of joints in the body, and ◦ the vitreous of the eye where it provides a clear, elastic gel that maintains the retina in its proper position. 34

Thank You 35