Carbohydrate Chemistry I PDF

Biochemistry of Carbohydrates Dr/ Nashwa Abdelghaffar Abdel Rahman Maghraby Medical Biochemistry Department ▪ Carbohydrates are substances containing carbon, hydrogen and oxygen ▪ Carbohydrates are aldehyde (CHO) or ketone (C=O) derivatives of polyhydric alcohols (have more than on...

Biochemistry of Carbohydrates Dr/ Nashwa Abdelghaffar Abdel Rahman Maghraby Medical Biochemistry Department ▪ Carbohydrates are substances containing carbon, hydrogen and oxygen ▪ Carbohydrates are aldehyde (CHO) or ketone (C=O) derivatives of polyhydric alcohols (have more than one OH group) or compounds which yield these derivatives on hydrolysis  Importance of carbohydrates 1. The chief source of energy. 2. Important structural components in animal and plant cells. 3. Important part of nucleic acids and free nucleotides and coenzymes. 4. Major antigens are carbohydrates in nature, e.g., blood group substance. 5. Has a biological role as a part of hormones and their receptors and enzymes. Monosaccharides 4. Hexoses: monosaccharides containing 6 carbon atoms. a. Aldohexoses: glucose, mannose, and galactose. b. Ketohexose: fructose. Importance (functions) of Hexoses: 1- Glucose: “grape sugar” - - It is is the most important sugar of carbohydrate: - Glucose is the main sugar in blood - Glucose is one of major sources of energy in the body. - In the liver and other tissues, glucose is converted to all carbohydrates in the body e.g. glycogen, galactose, - It is produced by hydrolysis of starch, dextrins, glycogen, sucrose, maltose and lactose - It appears in urine in diabetes mellitus.  2- Galactose - It can be converted into glucose in the liver. - It is synthesized in mammary gland to make the lactose of milk (milk sugar) - It enters in structure of glycoproteins, glycolipids and mucopolysaccharides in its amine form  3- Fructose: “fruit / semen sugar ” - It is called(or levoulose) because is levorotatory - It is the sweetest sugar known. - It is the main sugar in bee's honey and fruits. - - It is the main sugar of semen - It is obtained from inulin and sucrose hydrolysis - It can be converted into glucose in the liver. 4- Mannose - A constituent of many glycoproteins and sialic acid - Isolated from plant mannans; hence the name Ring (cyclic) structure of sugars  Glyceraldehyde ▪ Is the carbon atom to which 4 different groups or atoms are attached. ▪ Glyceraldehyde is called the reference sugar because it contains one asymmetric carbon atom. ▪ Any substance containing asymmetric carbon atom shows 2 Properties, ✓ Optical activity and ✓ Optical isomerism.  Optical activity ▪ It is the ability of substance to rotate plane polarized light either to the right or to the left. ✓ If the substance rotates plane polarized light to the right so it is called: dextrorotatory or d or (+). ✓ If substance rotates it to the left so it is called: levorotatory or I or (-). ▪ Glucose contains 4 asymmetric carbon atoms. It is dextrorotatory, so it is sometimes named dextrose. ▪ Fructose contains 3 asymmetric carbon atoms. It is levorotatory. so it is sometimes called: LevuIose  Optical isomerism ▪ It is the ability of substance to present in more than one form (isomer). ▪ Isomers are substances which have the same molecular formula but differ in ✓ Distribution of their. atoms into groups (Structural isomerism). ✓ Distribution of these groups and atoms in the space around carbon atoms (Stereo-isomerism).  Structural isomerism - They are isomers that have different structure due to different ways of arrangement of atoms and groups forming the molecule. - Types of structural isomerism are 4 : ✓ Ring isomerism ✓ Functional group isomerism ✓ Positional isomerism ✓ Chain isomerism  Ring isomerism Functional group isomerism (Aldose-Ketose isomerism) EX: - glucopyranose & glucofuranose, EX: - Fructose & glucose - fructopyranose & fructofuranose - erythrose & erythrulose -ribose&ribulose,  Stereo-isomerism - They are molecules having the same structure but differ in position of their different groups and atoms in the space, i.e., in spatial configuration. - The number of stereoisomers = 2n, where n is the number of asymmetric carbon atoms. - There are four types of stereo-isomerism as follows: ✓ D and L isomerism (enantiomers): ✓ Anomers ✓ Epimers ✓ Geometric isomerism D and L isomerism (enantiomers): ▪ They differ in distribution of H and OH groups around the sub-terminal asymmetric carbon atoms. ✓D form has the OH group to the right of the sub-terminal carbon atom (i.e., adjacent to the terminal primary alcohol group-reference carbon atom). ✓L form has the OH on the left ▪ Metabolizable sugars in human body are D-forms only. ▪ Examples are ✓ D- glyceraldehyde and L- glyceraldehyde ✓D-glucose and L-glucose. or ✓D-mannose and L-mannose. Anomers: - They are stereoisomers which differ in distribution of H and OH group around the asymmetric anomeric carbon atom after cyclization of the molecule ✓ C1 in aldoses or ✓ C2 in ketoses - Examples - and -glucose are anomers. Epimers: ▪ Epimers are isomers having more than asymmetric carbon, all are same except only one is different. ✓ Glucose & Mannose are epimers at carbons 2. ✓ Glucose & Galactose are epimers at carbons 4. 1. Sugar acids 2. Sugar alcohols 3. Deoxy sugars 4. Amino sugars 5. Amino sugar acids  Sugar acids - Are produced by oxidation of carbonyl carbon, last carbon or both - L-Ascorbic acid (vitamin C) is an important sugar acid  CHO COOH H C OH H C OH HO C H bromine water, O2 HO C H H C OH H C OH H C OH H C OH CH 2OH CH 2OH D-Glucose D-Gluconic acid CHO CHO H C OH H C OH HO C H H2O2 HO C H H C OH Dil. Nitric acid H C OH H C OH H C OH CH 2OH COOH D-Glucose D-Glucuronic acid CHO COOH H C OH H C OH HO C H O2 HO C H H C OH Conc. Nitric acid H C OH H C OH H C OH CH 2OH COOH D-Glucose D-Glucaric acid  Sugar alcohols Are produced by Reduction of carbonyl carbon Mannitol is injected intravenously to reduce intracranial hypertension in cases of meningitis, cerebral hemorrhage or thrombosis and Is used in kidney function testing  CHO CH2OH CHO CH2OH H2 H C OH H C OH H C OH H C OH HO C H H2 HO C H Na amalgum, H2SO4 CH2OH CH2OH H C OH H C OH Na amalgum, H2SO4 Glyceraldehyde Glycerol H C OH H C OH CH2OH CH2OH Glucose Sorbitol CHO CH2OH CH2OH CH2OH CH2OH H C OH H C OH H C OH C=O HO C H H C OH H2 H C OH HO C H HO C H HO C H H2 H C OH Na amalgum, H2SO4 H C OH H C OH OR H C OH H C OH Na amalgum, H SO 2 4 CH 2OH CH2OH H C OH H C OH H C OH Ribose Ribitol CH2OH CH2OH CH2OH Fructose Sorbitol Mannitol CHO CH 2OH CHO CH 2OH HO C H HO C H H C OH H C OH HO C H H2 HO C H HO C H H2 HO C H H C OH H C OH HO C H Na amalgum, H2SO4 Na amalgum, H2SO4 HO C H H C OH H C OH H C OH H C OH CH 2OH CH 2OH CH 2OH CH 2OH Mannose Mannitol Galactose Dulcitol  3- Deoxysugars ▪ Are produced by replacement of hydroxyl groups by hydrogen atom i.e. one oxygen is missed. ▪ This may occur at either of three places: 1. At C2 gives Deoxy sugar proper, e.g., deoxyribose that enters in structure of DNA., 2. At C6 gives methyl pentoses (Methylose), ✓ L-galactose gives L-fucose enter in the structure of glycoproteins, e.g., blood group substance 3. At C3, as in Sialic acid,  4- Amino sugars ▪ In these sugars, the hydroxyl group attached to C2 is replaced by ✓ an amino or ✓an acetyl-amino group. ▪ Amino sugars enter in glycoproteins. ▪ Examples: ✓ Glucosamine: It enters in heparin and hyaluronic acid ✓ Galactosamine: It enters in chondroitin sulphate. ✓ Mannosamine: It enters in neuraminic and sialic acids..  5- Amino sugar acids ▪ Formed by addition of amino sugars and some acids. ▪ Examples: ✓ Neuraminic acid = Mannosamine + pyruvic acid. 9C ✓ Sialic acid or N-acetylneuraminic acid (NANA) enters in glycolipid.  Disaccharides 1. Reducing Disaccharides ✓ Maltose ✓ Isomaltose ✓ Cellobiose ✓ Lactose 2. Non-Reducing Disaccharides ✓Sucrose ✓Trehlose  Disaccharides ▪ The most Important disaccharide are: 1. Maltose = α-glucose + α -glucose (α 1 - 4 glycosidic bond ). 2. Isomaltose = α - glucose + α -glucose (α 1 - 6 glycosidic bond). 3. Trehalose = α - glucose + α -glucose (α 1 - 1 glycosidic bond). 4. Cellobiose = β - glucose + β -glucose (β 1 - 4 glycosidic bond). 5. Lactose = β- glucose + β - galactose (β 1 - 4 glycosidic bond). 6. Sucrose = α -glucose + β -fructose (α 1 - β 2 glycosidic bond). ▪ Properties: all disaccharide except (trehalose & Sucrose) showing the following characters : ✓ It is a reducing agent (can reduce Benedict’s reagent). ✓ It can be present in α and β forms. ✓ It can form characteristic osazone crystals.  A. Reducing Disaccharides Maltose (malt sugar) It consists of 2 -glucose units linked by -1,4-glucosidic linkage It is produced during digestion of starch. It is hydrolyzed by acids and in human intestine by maltase enzyme. CH 2OH CH 2OH O O H H OH..... H H H 1 4 H H OH H OH O H..... OH OH H OH H OH -Glucose Glucose − and −Maltose  Lactose (milk sugar) ▪ It is formed of β -galactose and β -glucose linked by 1,4-glucosidic linkage ✓ β -galactose participates by C1 ✓ β -glucose participates by C4 ▪ It is excreted in urine of pregnant and lactating females ▪ It is the most suitable sugar for baby feeding as a sweetener for milk because: 1. It is the least sweet sugar so that the baby can nurse a large amount of mother’s milk without getting his appetite lost. 2. Because it has a B-glycosidic linkage it is non-fermentable sugar, so it does not form gases and not cause colic to the infant. 3. It has a laxative effect and prevents constipation and non-irritant to the stomach and does not cause vomiting. 4. Unabsorbed sugar is used as a food for large intestinal bacteria that form a number of vitamins that benefits the baby. 5. It is easily digested and helps absorption of the minerals of milk.  Cellobiose - It is formed of 2 -glucose units linked by -1,4-glucosidic linkage. - It is a reducing disaccharide. - It is the building unit of cellulose. CH 2OH CH 2OH O O H OH H H H 1 O 4 H OH H OH H H OH H OH H OH -Glucose -Glucose Cellobiose  B. Non-reducing Disaccharides 1. Sucrose (invert sugar) It is table sugar and sugar of cane and molasses It is formed of -glucose linked to -fructose by --1,2-linkage. It is a fermentable sugar. The 2 anomeric carbons (C1 of glucose and C2 of fructose) are involved in the linkage, therefore it is: CH 2OH O H ✓ Non-reducing sugar. -Glucose H H 1 OH H ✓ Non osazone forming. OH H OH ✓ Not mutarotating. CH 2OH O O ✓ Not having  or -forms. -Fructose OH 2 H H CH 2OH OH H  It is a dextrorotatory sugar but when it is hydrolyzed by sucrase enzyme or by acid hydrolysis (HCl) the mixture of sugars produced is levorotatory. This is because the levorotatory power of fructose (-92.5) cancels the dextrorotatory power of glucose (+52.5) since they are at equal proportions in the product. This is why this sugar is called invert sugar. - Sucrase enzyme is therefore, also called invertase enzyme.  2. Trehalose It is formed of 2 -glucose units linked by -1,1-glucosidic linkage. Present in ✓ a highly toxic lipid extracted from Mycobacterium tuberculosis. ✓ It is the major sugar of insect hemolymph ✓ fungi and yeast. CH2OH O H OH H H H H H OH H 1 1 OH H HOH2C O OH OH O H OH H -Glucose -Glucose Trehalose All the following are sugar alcohols, EXCEPT: a- Galactitol b- Mannitol c- Xylulose d- Sorbitol Ribitol is: a. Deoxysugar b- Sugar alcohol c- Amino sugar d- Sugar acid Sorbitol is produced by reduction of: a- Glucose or fructose b- Glucose or galactose c- Glucose or mannose d- Galactose or fructose 1. A triose sugar is (A) Glycerose (B) Ribose (C) Erythrose (D) Fructose 2. A pentose sugar is (A) Dihydroxyacetone (B) Ribulose (C) Erythrose (D) Glucose 3. The number of isomers of glucose is (A) 2 (B) 4 (C) 8 (D) 16 4. Two sugars which differ from one another only in configuration around a single carbon atom are termed (A) Epimers (B) Anomers (C) Optical isomers (D) Stereoisomers 1. Isomers differing as a result of variations in configuration of the —OH and —H on carbon atoms 2, 3 and 4 of glucose are known as (A) Epimers (B) Anomers (C) Optical isomers (D) Steroisome 2. The most important epimer of glucose is (A) Galactose (B) Fructose (C) Arabinose (D) Xylose 3. α-D-glucose and β -D-glucose are (A) Stereoisomers (B) Epimers (C) Anomers (D) Keto-aldo pairs 4. Compounds having the same structural formula but differing in spatial configuration are known as (A) Stereoisomers (B) Anomers (C) Optical isomers (D) Epimers 5. The sugar found in DNA is (A) Xylose (B) Ribose (C) Deoxyribose (D) Ribulose The sugar found in milk is: a- Galactose b- Glucose. c- Fructose. d- Lactose. The glycosidic linkage seen in sucrose is: a- Alpha linkage b- Beta 1-4 linkage c- Alpha 1-6 linkage d- Alpha 1-2 linkage Sucrose consists of: a- α Glucose + β glucose b- α Glucose + β fructose c- α Glucose + β galactose d- α Glucose + β mannose Which is a non-reducing sugar? a- Maltose b- Sucrose c- Lactose d- Isomaltose The glycosidic linkage seen in lactose is: a- Alpha 1-4 linkage b- Beta 1-4 linkage c- Alpha 1-6 linkage d- Alpha 1-2 linkage The glycosidic linkage seen in lactose is: a- Alpha 1-4 linkage b- Beta 1-4 linkage c- Alpha 1-6 linkage d- Alpha 1-2 linkage The glycosidic linkage seen in maltose is: a- Alpha 1-4 linkage b- Beta 1-4 linkage c- Alpha 1-6 linkage d- Alpha 1-2 linkage Hydrolysis of maltose will give rise to: a. Glucose only b- Glucose and fructose c- Glucose and galactose d- Glucose and mannose 24. Lactose by hydrolysis gives: a- 2 glucose molecules b- Glucose and mannose. c- Fructose and galactose. d- Glucose and galactose.