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Carbohydrates Dr Seemal Jelani Introduction to Biochemistry 1 5/23/2017 Carbohydrates Most abundant Their abundance in human body is low but constitute about 75% by mass of dry plant materials Green (chlorophyll-containing) plants produce carbohydrates via photosynthesis A major source of energy from our diet composed of the elements C, H and O. They also called saccharides, which means “sugars.” Dr Seemal Jelani Biochemistry Introduction to 2 5/23/2017 Carbohydrates They are produced by photosynthesis in plants. such as glucose are synthesized in plants from CO2 from the air, H2O from the soil, and energy from the sun absorbed in chlorophyll to form carbohydrates and O2 Oxidized in living cells to produce CO2, H2O, and energy. Dr Seemal Jelani Biochemistry Introduction to 3 5/23/2017 Uses of carbohydrates in plants Cellulose (carbohydrates) serve as structural elements Starch (carbohydrates) provide energy reserves for the plants Dr Seemal Jelani Biochemistry Introduction to 4 5/23/2017 Dietary intake of plant materials is the major carbohydrate source for humans and animals Functions: Carbohydrate oxidation provides energy Carbohydrate storage in the form of glycogen provides a short-term energy reserve Carbohydrates supply carbon atoms for the synthesis of other biochemical substances (proteins, lipids, nucleic acids) Carbohydrate form part of the structural framework of DNA and RNA Dr Seemal Jelani Biochemistry Introduction to 5 5/23/2017 Classification of Carbohydrates The types of carbohydrates are • Monosaccharides, the simplest carbohydrates. • Disaccharides, which consist of two monosaccharides. • Polysaccharides, which contain many monosaccharides. Dr Seemal Jelani Biochemistry Introduction to 6 5/23/2017 General Formula Cn H2n On Carbohydrates are Polyhydroxy aldehydes, Polyhydroxy ketones The carbohydrate glucose is Polyhydroxy aldehyde and the carbohydrate fructose is Polyhydroxy ketone Dr Seemal Jelani Biochemistry Introduction to 7 5/23/2017 CHIRALITY: Handedness in molecules A chiral object is not superimposable on its mirror image they do not possess a plane of symmetry Two forms of a chiral object are known as enantiomers dr seemal jelani 8 5/23/2017 Mirror image dr seemal jelani 9 5/23/2017 Mirror image dr seemal jelani 10 5/23/2017 Non superposable dr seemal jelani 11 5/23/2017 Chiral HANDS dr seemal jelani 12 5/23/2017 Chiral dr seemal jelani Shells 13 5/23/2017 The plane has the same thing on both sides for the flask There is no mirror plane for a hand dr seemal jelani 14 5/23/2017 If an object has a plane of symmetry it is necessarily the same as its mirror image The lack of a plane of symmetry is called “handedness”, Chirality dr seemal jelani 15 5/23/2017 Hands, gloves are prime examples of chiral object They have a “left” and a “right” version dr seemal jelani 16 5/23/2017 Why this chapter? Handedness is important in organic and biochemistry Molecular handedness makes possible specific interactions between enzymes and substrates dr seemal jelani 17 5/23/2017 Chirality in daily life Most Biomolecules in nature are chiral (sugars, DNA, proteins, amino acids, steroids) Human proteins are exclusively built from L-amino acids; this involves receptors which are chiral dr seemal jelani 18 5/23/2017 The Reason for Handedness: Chirality Molecules that are not superimposable with their mirror images are chiral (have handedness) A plane of symmetry divides an entire molecule into two pieces that are exact mirror images dr seemal jelani 19 5/23/2017 Functional groups in carbohydrates Aldehydes CHO Ketone C=O Dr Seemal Jelani Biochemistry Introduction to Aldose Ketose 20 5/23/2017 Chirality in carbohydrates Fischer projections Carbohydrates may contain more than one chiral center FP represents a method for giving molecularity specifications in two dimensions FP is a two dimensional notation for showing the spatial arrangement of groups about chiral centers in molecule Dr Seemal Jelani Biochemistry Introduction to 21 5/23/2017 Stereoisomers Enantiomers Diastereomers Handedness (Right and left) D and L Fischer Projection for 2,3,4-trihydroxybutanal Epimers Dr Seemal Jelani Biochemistry Introduction to 22 5/23/2017 Properties of Enantiomers Structural isomers have different properties Diastereoisomers have different properties Enantiomers have same properties expect two: Their interaction with plane polarized light Their interaction with other chiral substances Dr Seemal Jelani Biochemistry Introduction to 23 5/23/2017 PLANE-POLARIZED LIGHT Polarimeter: a device for measuring the extent of rotation of plane-polarized light Dr Seemal Jelani Chem-241 24 5/23/2017 Plane-Polarized Light optical activity Light vibrating in all planes to direction of propagation Plane-polarized light: light vibrating only in parallel planes Plane-polarized light the vector sum of left and right circularly polarized light Optically Activity Enantiomers (chiral) interact with circularly polarized light rotating the plane one way with R center and opposite way with S result: rotation of plane-polarized light clockwise (+) or counterclockwise (-) Plane-Polarized Light Change in the polarized plane? (polarimeter) achiral sample no change in the plane Plane-Polarized Light Change in the polarized plane? (polarimeter) rotates the plane Classification of Monosaccharides Monosaccharides consist of 3-6 carbon atoms typically. A carbonyl group (aldehyde or ketone). Several hydroxyl groups. 2 types of monosaccharide structures: Aldoses and ketoses Dr Seemal Jelani Biochemistry Introduction to 29 5/23/2017 Aldoses O ║ C─H aldose │ H─ C─OH │ H─ C─OH │ CH2OH Aldoses are monosaccharides with an aldehyde group with many hydroxyl (-OH) groups. triose (3C atoms) tetrose (4C atoms) pentose (5 C atoms) hexose (6 C atoms) Erythose, an aldotetrose Dr Seemal Jelani Biochemistry Introduction to 30 5/23/2017 Ketoses CH2OH │ C=O ketose │ H─ C─OH │ H─ C─OH │ H─C─OH │ CH2OH Ketoses are monosaccharides with a ketone group with many hydroxyl (-OH) groups. Fructose, a ketohexose Dr Seemal Jelani Biochemistry Introduction to 31 5/23/2017 Learning Check Identify each as aldo- or keto- and as tetrose, pentose, or hexose: O CH2OH C H H C OH C O H C OH HO C H H C OH H C OH H C OH CH2OH CH2OH ketopentose aldohexose Dr Seemal Jelani Biochemistry Introduction to 32 5/23/2017 Structures of Monosaccharides Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings Dr Seemal Jelani Biochemistry Introduction to 33 5/23/2017 Fischer Projections A Fischer projection is used to represent carbohydrates. places the most oxidized group at the top. shows chiral carbons as the intersection of vertical and horizontal lines. Dr Seemal Jelani Biochemistry Introduction to 34 5/23/2017 Chiral Carbon Carbon linked to four different groups CH3CHOHC6H5 Dr Seemal Jelani Biochemistry Introduction to 35 5/23/2017 D and L Notations In a Fischer projection, the −OH group on the chiral carbon farthest from the carbonyl group determines an L or D isomer. left is assigned the letter L for the L-form. right is assigned the letter D for the D-form. Dr Seemal Jelani Biochemistry Introduction to 36 5/23/2017 Examples of D and L Isomers of Monosaccharides O O C H C H H O OH HO H H OH H OH CH2OH D-glucose Dr Seemal Jelani Biochemistry HO C H H OH H H OH OH CH2OH D-ribose Introduction to 37 H H OH H OH HO H CH2OH L-galactose 5/23/2017 D-Glucose found in fruits, corn syrup, and honey. an aldohexose with the formula C6H12O6 known as blood sugar in the body. The monosaccharide in polymers of starch, cellulose, and glycogen. Dr Seemal Jelani Biochemistry Introduction to 38 5/23/2017 D-Fructose is a ketohexose C6H12O6. is the sweetest carbohydrate. CH2OH C O HO C H is found in fruit juices and honey. H C OH H C OH converts to glucose in the body. CH2OH D-Fructose Dr Seemal Jelani Biochemistry Introduction to 39 5/23/2017 Cyclic Structures Cyclic structures are the widespread form of monosaccharides with 5 or 6 carbon atoms. O O Dr Seemal Jelani Biochemistry Introduction to 40 5/23/2017 The cyclic forms of monosaccharides result from the ability of their carbonyl group to react intramolecularly with a –OH group Cyclic structure is formed when the –OH group on C-5 reacts with the aldehyde group or ketone group The result is a cyclic hemiacetal or cyclic hemiketal Dr Seemal Jelani Biochemistry Introduction to 41 5/23/2017 Steps for cyclisation for D-Glucose All –OH groups to the right in the projection formula appear below the ring whereas –OH gps to the left in FP appear above the ring Dr Seemal Jelani Biochemistry Introduction to 42 5/23/2017 Drawing the Cyclic Structure for Glucose Number the carbon chain and turn clockwise to linear open chain. H O H H OH H C 1 H 2C OH HO 3C H H 4C OH H 5C OH 6CH Dr Seemal Jelani Biochemistry form a O HOCH2 C C C C C H OH OH H OH 6 5 4 3 2 1 2OH Introduction to 43 5/23/2017 The –OH gp on C-5 adds across then C=O to give two stereoisomers In aq. Solu of D- glucose, a dynamic equilibrium exists among the α, β, and open chain forms and there is continual interconversion among them A freshly mixed solution of pure α- D- Glucose slowly converts to a mixture of both α & β-D-glucose by an opening and closing of the cyclic structure. At equilibrium 63% is β-D-glucose and 37% are α-Dglucose and less than 0.01% in open chain Dr Seemal Jelani Biochemistry Introduction to 44 5/23/2017 Cyclic Structure for Glucose STEP 2 Fold into a hexagon. Bond the C5 –O– to C1. Place the C6 group above the ring. Write the –OH groups on C2 and C4 below the ring. Write the –OH group on C3 above the ring. Write a new –OH on C1. Dr Seemal Jelani Biochemistry Introduction to 45 CH2OH 6 5 O 4 OH 1 OH 3 2 OH OH 5/23/2017 Cyclic Structure for Glucose (cont) STEP 3 Write the new –OH on C1 • down for the form. • up for the form. CH2OH O CH2OH O OH OH OH OH OH OH OH OH -D-Glucose Dr Seemal Jelani Biochemistry Introduction to -D-Glucose 46 5/23/2017 Summary of the Formation of Cyclic Glucose Dr Seemal Jelani Biochemistry Introduction to 47 5/23/2017 Alcohols react with the carbonyl groups of aldehydes and ketones to give hemiacetal Dr Seemal Jelani Biochemistry Introduction to 48 5/23/2017 -D-Glucose and β-D-Glucose in Solution When placed in solution, cyclic structures open and close. -D-glucose converts to β-D-glucose and vice versa. at any time, only a small amount of open chain forms. CH2OH CH2OH O OH OH Dr Seemal Jelani Biochemistry O O C OH H OH OH OH -D-glucose (36%) H O OH OH CH2OH D-glucose (open) (trace) Introduction to 49 OH OH OH β-D-glucose (64%) 5/23/2017 Intramolecular Cyclic hemiketal Structure of Fructose Fructose and other ketoses with a long carbon chain also cyclizes to form hemiketal D-fructose and D-ribose form a fivemembered ring Dr Seemal Jelani Biochemistry Introduction to 50 5/23/2017 Cyclic Structure of Fructose Fructose is a ketohexose. forms a cyclic structure. reacts the —OH on C-5 with the C=O on C-2. CH2OH C O CH2OH HO C H CH2OH OH H C OH H C OH CH2OH O O OH OH OH CH2OH OH OH α-D-fructose -D-fructose CH2OH D-fructose Dr Seemal Jelani Biochemistry Introduction to 51 5/23/2017 Haworth Projection This is two dimensional notation that specifies the 3dimensional structure of cyclic form of carbohydrate Dr Seemal Jelani Biochemistry Introduction to 52 5/23/2017 The D and L form of a monosaccharide is determined by the position of the terminal CH2OH gp on the highest-numbered ring carbon atom In D-form, this group is positioned above the ring In L-form the terminal CH2OH gp is positioned below the ring (not encountered in biological systems) Dr Seemal Jelani Biochemistry Introduction to 53 5/23/2017 α and β configurations is determined by the position of the –OH gp on carbon no 1 relative to the CH2OH In β-configuration both of these gps point in the same direction In α-configuration the two gps point in opposites direction Dr Seemal Jelani Biochemistry Introduction to 54 5/23/2017 Reactions of Monosaccharides Oxidation Reduction Glycoside formation Phosphate ester formation Amino sugar formation Dr Seemal Jelani Biochemistry Introduction to 55 5/23/2017 Oxidation Yield three different types of oxidation products Oxidizing agent used to determined the product Weak oxidizing Agent: Tollen's Reagent Benedict Solution Reducing Sugars Is a carbohydrate that gives a positive test with TR, FS and BS Dr Seemal Jelani Biochemistry Introduction to 56 5/23/2017 Strong oxidizing agent oxidizes both end of monosaccharide i.e Terminal pri-alcohol and carbonyl group to give dicarboxylic acid Such polyhydroxy dicarboxylic acids are known as – aric acids The oxidation of glucose gives Glucaric acid Dr Seemal Jelani Biochemistry Introduction to 57 5/23/2017 Reduction Carbonyl group present in a monosaccharide ( aldose, ketose) can be reduced to a Hydroxyl group using Hydrogen as a reducing group Product is called Sugar Alcohol D- Glucitol is also known as D-sorbitol These are used as moisturizing agents in foods and cosmetics because of their affinity for water Dr Seemal Jelani Biochemistry Introduction to 58 5/23/2017 Glycoside Formation Cyclic forms of monosaccharides are hemiacetals and hemiketals react with alcohols to form Acetals and Ketals The general name for monosaccharide acetals and Ketals is Glycoside Glycoside It is an Acetal or a Ketal formed from a cyclic monosaccharide Dr Seemal Jelani Biochemistry Introduction to 59 5/23/2017 Glycoside produced from glucose is Glycoside Glycoside produced from galactose is Galactoside Exist in α and β forms Named as by listing alkyl or aryl group attached to the oxygen followed by the name of a monosaccharide involved with the suffix-ide Dr Seemal Jelani Biochemistry Introduction to 60 5/23/2017 Phosphate Ester formation The –OH gp of a monosaccharide can react with Oxoacids to form Esters Phosphate esters are formed from phosphoric acid and various monosaccharides commonly encountered in biological system Example Specific enzymes in the body catalyze the esterification of the carbonyl group (C1) and the primary alcohol (C6) of glucose to give Glucose-1-Phosphate Glucose-6-Phosphate Dr Seemal Jelani Biochemistry Introduction to 61 5/23/2017 These phosphate esters of glucose are stable in aqueous solution and play important roles in the metabolism of carbohydrates Dr Seemal Jelani Biochemistry Introduction to 62 5/23/2017 Amino Sugar formation Amino sugars of glucose, mannose and galactose are common in nature They are produced by replacing the –OH group on carbon 2 on the monosaccharide with an amino group Amino sugars and their N-acetyl-derivatives are important building blocks of polysaccharides such as cartilage The N-acetyl derivatives of D-glucosamine and D-galactosamine are present in the biochemical markers on red blood cells, which distinguish the various blood type Dr Seemal Jelani Biochemistry Introduction to 63 5/23/2017 Disaccharides Dr Seemal Jelani Biochemistry Introduction to 64 5/23/2017 Important Disaccharides A disaccharide consists of two monosaccharides. Monosaccharides Dr Seemal Jelani Biochemistry Disaccharide glucose + glucose maltose + H2O glucose + galactose lactose + H2O glucose + fructose sucrose + H2O Introduction to 65 5/23/2017 Disaccharides Monosaccharide + Monosaccharide (Functioning as (Functioning as A hemiacetal or an alcohol) hemiketal) Disaccharide + H2O glycoside Dr Seemal Jelani Biochemistry Introduction to 66 5/23/2017 Maltose Maltose is A disaccharide also known as malt sugar. Composed of two D-glucose molecules. Obtained from the hydrolysis of starch. Used in cereals, candies, and brewing. Found in both the - and β - forms. The Glycosidic linkage between the two glucose units is called (1-4) linkage Dr Seemal Jelani Biochemistry Introduction to 67 5/23/2017 Glycosidic Formation Cyclic forms of monosaccharides are hemiacetals and hemiketals, they react with alcohols to form acetals and Ketals The bond that links two monosaccharides of a disaccharide together is called a Glycosidic linkage A Glycosidic linkage is the carbon-Oxygen-carbon bond that joins the two components of Glycoside together Dr Seemal Jelani Biochemistry Introduction to 68 5/23/2017 Formation of Maltose Free α-OH Dr Seemal Jelani Biochemistry Introduction to 69 5/23/2017 Cellobiose Produced as an intermediate in the hydrolysis of the polysaccharide cellulose Contains two D-glucose monosaccharide units Differ from maltose –must have a β- configuration β- (1-4)Glycosidic linkage Reducing sugar having three isomeric forms in Aq. Solu and on hydrolysis produces two D-glucose molecules Dr Seemal Jelani Biochemistry Introduction to 70 5/23/2017 Difference in maltose and Cellobiose Different in biological behaviors Differences are related to stereochemistry of their glycosidic linkages Maltase enzyme which breaks glucose-glucose α (1-4) linkage present in maltose is present in maltose is found in human body and in yeast That’s why maltose is easily digested by human body and readily fermented by yeast Dr Seemal Jelani Biochemistry Introduction to 71 5/23/2017 Both the human body and yeast lacks enzyme cellobiase which is needed to break the glucoseglucose β (1-4) glycosidic linkage of Cellobiose Cellobiose cannot be digested by humans or fermented by yeast Dr Seemal Jelani Biochemistry Introduction to 72 5/23/2017 Lactose Lactose is a disaccharide of β-Dgalactose and α- Dglucose. contains a β -1,4glycosidic bond. α-form is found in milk nearly 49% and milk products. α-form Dr Seemal Jelani Biochemistry Introduction to 73 5/23/2017 Sucrose Sucrose or table sugar • is obtained from sugar cane and sugar beets. • consists of α-D-glucose and β-D-fructose.. • has an α,β-1,2-glycosidic bond. α-D-glucose β -D-fructose Dr Seemal Jelani Biochemistry Introduction to 74 5/23/2017 Sweetness of Sweeteners Sugars and artificial sweeteners differ in sweetness. are compared to sucrose (table sugar), which is assigned a value of 100. Dr Seemal Jelani Biochemistry Introduction to 60 000 75 5/23/2017 Learning Check Identify the monosaccharides in each of the following: A. lactose (1) α-D-glucose (2) β-D-fructose (3) β-D-galactose B. maltose (1) α-D-glucose (2) β-D-fructose (3) β-D-galactose C. sucrose (1) α-D-glucose (2) β-D-fructose (3) β-D-galactose Dr Seemal Jelani Biochemistry Introduction to 76 5/23/2017 Polysaccharides Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings Dr Seemal Jelani Biochemistry Introduction to 77 5/23/2017 Polysaccharides Polysaccharides Are polymers of D-glucose. Include Amylose and Amylopectin, starches made of α-D-glucose. Include glycogen (animal starch in muscle), which is made of α-D-glucose. Include cellulose (plants and wood), which is made of β-D-glucose. Dr Seemal Jelani Biochemistry Introduction to 78 CH2OH O OH OH OH OH α-D-Glucose 5/23/2017 Structures of Amylose and Amylopectin Dr Seemal Jelani Biochemistry Introduction to 79 5/23/2017 Amylose Amylose is a polymer of α-Dglucose molecules. linked by -1,4 glycosidic bonds. a continuous (unbranched) chain. Dr Seemal Jelani Biochemistry Introduction to 80 5/23/2017 Amylopectin Amylopectin is a polymer of α-Dglucose molecules. is a branched-chain polysaccharide. has α-1,4-glycosidic bonds between the glucose units. has α-1,6 bonds to branches. Dr Seemal Jelani Biochemistry Introduction to 81 5/23/2017 Dextrins Starches like amylose and amylopectin hydrolyze to dextrins (smaller polysaccharides) Contain 3-8 glucose units Dr Seemal Jelani Biochemistry Introduction to 82 5/23/2017 Glycogen Glycogen is the polysaccharide that stores α-D-glucose in muscle. is similar to amylopectin, but is more highly branched. Dr Seemal Jelani Biochemistry Introduction to 83 5/23/2017 Cellulose Cellulose is a polysaccharide of glucose units in unbranched chains. has β-1,4-glycosidic bonds. cannot be digested by humans because humans cannot break down β-1,4-glycosidic bonds. Dr Seemal Jelani Biochemistry Introduction to 84 5/23/2017