Carbohydrate Chemistry PDF

CARBOHYDRATE CHEMISTRY Presented by: Dr, Marwa Hussein Mohamed Lecturer of Biochemistry and Molecular Biology Objectives:- Explain the definition and functions of carbohydrates Classify carbohydrates according to their structure. Explain different types of monosaccharides and...

CARBOHYDRATE CHEMISTRY Presented by: Dr, Marwa Hussein Mohamed Lecturer of Biochemistry and Molecular Biology Objectives:- Explain the definition and functions of carbohydrates Classify carbohydrates according to their structure. Explain different types of monosaccharides and their characteristics. Illustrate various forms of isomerism. Explain important sugar derivatives structure and functions Clarify reducing and non-reducing disaccharides. Discuss polysaccharides structure and functions. Summarize complex carbohydrates.  Definition: 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. Polyhydroxy-aldehydes or polyhydroxy-ketones. General formula: (CH2O)n Have 3 to 7 carbons Example: (C3 H6 O3) Hydrogen and oxygen are present in 1:2 ratio the same ratio as water, so the French called them “Hydrates de Carbon”, i.e., carbo-hydrates Cn(H2O)n.  Importance of carbohydrates: 1. The chief source of energy. 2. Store energy in the form of: starch (in plants) glycogen (in animals and humans) 3. Supply carbon for synthesis of other compounds 4. Important structural components in animal and plant cells. 5. Important part of nucleic acids and free nucleotides and coenzymes. 6. Major antigens are carbohydrates in nature, e.g., blood group substance. 7. Biological role as a part of hormones and their receptors and enzymes. Classification of carbohydrates According to the number of sugar units in the molecule into Monosaccharides They contain one sugar unit, i.e., and the simplest (simple sugars): form of sugars and cannot be further hydrolyzed. Disaccharides: They contain 2 monosaccharide units per molecule They contain 3 – 10 monosaccharide units per Oligosaccharides: molecule and give monosaccharides on acid hydrolysis. They contain more than 10 monosaccharide units Polysaccharides per molecule and give monosaccharides on acid hydrolysis. Monosaccharides They are classified according to the number of carbon atoms (3- 7) into: Trioses, tetroses, pentoses, hexoses, and heptoses. Each of these groups is subdivided according to the type of functional chemical group into: Aldoses Ketoses (Polyhydroxy-aldhydes). (Polyhydroxy-ketones). Trioses: are monosaccharides containing 3 carbon atoms, e.g., A- Aldotriose: Example: glyceraldehyde CH2OH B- Ketotriose: Example: Dihydroxyacetone C=O CH2OH Tetroses: are monosaccharides containing 4 carbon atoms: A. Aldotetroses: CHO CHO CHO Example: Erythrose H C OH HO C H HO C H H C OH HO C H H C OH CH2OH CH2OH CH2OH D-Erythrose L-Erythrose D-Threos CH2OH CH2OH B. Ketotetroses C = O C = O H C OH HO C H Example: Erythrulose CH2OH CH2OH D-Erythrulose L-Erythrulose Pentoses: are monosaccharides containing 5 carbon atoms: CHO CHO CHO CHO A. Aldopentoses: H C OH HO C H HO C H H C OH Example: Ribose, xylose H C OH HO C H H C OH HO C H H C OH HO C H H C OH HO C H CH2OH CH2OH CH2OH CH2OH D-Ribose L-Ribose D-Arabinose L-Arabinose CH2OH CH2OH CH2OH CH2OH C=O C=O C=O C=O B. Ketopentose: H C OH HO C H HO C H H C OH H C OH HO C H H C OH HO C H Example: Ribulose, xylulose CH2OH CH2OH CH2OH CH2OH D-Ribulose L-Ribulose D-Xylulose L-Xylulose Hexoses: are monosaccharides containing 6 carbon atoms. CHO CHO CHO CHOCHO CHO CHO CHO CHO CHOCHO CHOCHO CHO CHO CH A. Aldohexoses: H C OHH HO C C OH HHHOC HO C OHHC HO HHO H H CH HO C C OH HC CH OH C HOHCHHO OHCOHHHHOC C Examples: glucose, mannose, galactose HO C HHO CH C OHHC HO H HO C H HO C H OH H OHCH HO C C OH HC HO C H HO C H OH H OHCH HO C C OH HC H C OHH HO C C OH HHHOC CH OHHC HO OHC H HO CH COHHHHOC HO C OHHC HO H HO H CH HO C C OH HC H C OHH HO C C OH HHHOC CH OHHC HO OHC H HO CH COHHHHOC CH OHHC HO OHCHHO H COHHHHOC C CH2OH CH2CH OH2OH CHCH 2OHCH2OHCH2CH 2OH OH2CH OH2OH CHCH 2OHCH2OHCH2CH 2OH OH2CH OH2OH CH D-GlucoseD-Glucose L-Glucose D-Mannose L-Glucose D-Glucose L-Mannose D-Mannose L-Glucose L-Mannose D-Galactose D-Mannose L-Galactose L-Mannose D-Galactose L D-Ga B. Ketohexoses: CH2OH CH2OH C = O C = O Examples: Fructose HO C H H C OH H C OH HO C H H C OH HO C H CH2OH CH2OH D-Fructose L-Fructose ASYMMETRIC CARBON ATOM: - Asymmetric carbon atom is the carbon atom attached to which 4 different groups or atoms. ASYMMETRIC CARBON ATOM: Carbonyl Carbon - An OH (hydroxyl) group is attached to each carbon except one, which is double bonded to an oxygen (carbonyl carbon). Cyclic structure of monosaccharides A cyclic structure is formed by reaction between the aldehyde or keto group with an alcohol group of the same sugar, making carbonyl carbon asymmetric (now referred as anomeric carbon). The ring structure is either: - Pyran (six-membered ring) - Furan (five-membered ring) Haworth's projection formula: Because Fisher’s formula could not explain some of the chemical and physical characteristics of sugars, Haworth put forth his projection formula. Haworth projection: the molecule is viewed from the side and above the plane of the ring. C and O atoms of the ring are drawn in the plane of the page. H and OH or other side groups are written on perpendicular plane. All groups located on the left side of fisher’s are written upwards. All groups located on the right side of fisher’s are written downwards.  Glucopyranose is formed by reaction between the aldehyde group with subterminal (C5) hydroxyl group of glucose. For glucose in solution, more than 99% is in the pyranose form. H OH HO H C C CH2OH CH2OH H C OH O H C OH O H H OH H H H HO C H HO C H OH H OH H H C OH H C OH H OH OH OH H C O H C O H OH H OH CH2OH CH2OH -D-glucopyranose -D-glucopyranose Glucofuranose is formed by reaction between the aldehyde group with hydroxyl group of C4 on the same glucose H OH HO H C 6 CH2OH C 6 CH2OH H C OH 5 CHOH O H C OH 5 CHOH O H OH HO C H HO C H 4 OH H 1 4 OH H 1 H C O H C O 3 2 H H 3 2 OH H H C OH H C OH CH2OH OH CH2OH H OH H -D-glucofuranose -D-glucofuranose  Fructopyranose is formed by reaction between the keto group with terminal (C6) hydroxyl group of fructose. Fructofuranose is formed by reaction between the keto group with subterminal (C5) hydroxyl group of fructose CH2OH CH2OH 6CH2OH H C OH O 1CH2OH C OH O H 6 1CH2OH HO C H 5 HO C H H OH 2 H C OH H H C OH 5 2 H 4 3 OH H OH H C O H C OH OH 4 3 OH CH2OH OH H CH2 O OH H -D-fructofuranose -D-fructopyranose  Importance of asymmetric carbon atom: Any compound containing asymmetric carbon atom has the following two properties: 1. It makes the compound optically active. 2. Isomerism is created around it.  Ordinary light vibrates in all directions. Ordinary light can be changed to plane polarized light by passing it through a prism made of calcium carbonate. Plane polarized light vibrates in one plane and direction. OPTICAL ACTIVITY Definition: It is the ability of the sugar to rotate the plane of the plane polarized light. The sugar that rotates the light to the right is called dextrorotatory (D or +) such as glucose, galactose and starch and that rotating light to the left is called levorotatory (L or -) such as fructose. Straight chain structure of typical monosaccharide (Glucose)  ISOMERISM Isomers are substances which have the same molecular formula but differ in distribution of their atoms into groups or distribution of these groups and atoms in the space around carbon atoms. e.g. fructose, glucose, mannose, and galactose are isomers of each other having formula C6H12O6 Asymmetric Carbon is an important determinant of Isomerism  ISOMERISM Almost all monosaccharides (except dihydroxy acetone)contain at least one asymmetrical carbon atom (chiral center) and are, therefore, have optical activity (ability to rotate plane polarized light) and optical isomers. The number of isomers is obtained by the formula 2𝑛 n=No of asymmetric carbons atom Forms of Isomerism Monosaccharides exhibit various forms of isomerism: Because they have asymmetric carbon atom ✓ Aldose and Ketose isomerism. ✓Pyranose and Furanose ring structures. ✓D and L Enantiomers. ✓Alphaα and Betaβ anomers. ✓Epimers.  FUNCTIONAL GROUP ISOMERISM Aldose and Ketose isomerism. - These are isomers that have the same carbon skeleton, the same position of substituent group but have different functional group (aldo-/keto-). Aldehydes such as; Ketones such as; Glyceraldehyde, Dihydroxyacetone, Erythrose, Erythrulose, Ribose, Xylose Ribulose, Xylulose, Glucose Fructose  RING ISOMERISM Pyran/furan forms such as glucopyranose and glucofuranose, and fructopyranose and fructofuranose. CH2OH CH2OH 6CH2OH H C OH O 1CH2OH C OH O H 6 1CH2OH HO C H 5 HO C H H OH 2 H C OH H H C OH 5 2 H 4 3 OH H OH H C O H C OH OH 4 3 OH CH2OH OH H CH2 O OH H -D-fructofuranose -D-fructopyranose  D AND L ISOMERISM ENANTIOMERS They differ in distribution of H and OH groups around the asymmetric carbon farthest from the carbonyl group (the sub- terminal carbon or C5). D form has the OH group to the right of the sub-terminal carbon atom. whereas it is on the left in L form. This difference make the two forms (D and L) mirror image to each other due to the change of the position of all H and OH groups into the opposite direction of D form in L form.  They are related to glyceraldehyde which exists in two isomers D and L irrespective o of its optical activity. CHO CHO H C OH HO C H CH2OH CH2OH D-Glyceraldehyde L-Glyceraldehyde OH group on sub-terminal OH group on sub-terminal carbon is written on right side. carbon is written on left side. Most of the naturally occurring monosaccharides are D-sugars. The enzymes responsible for their metabolism are specific for this configuration.  ANOMERS The cyclic structure of aldoses are hemiacetal, since it is formed by reaction between an aldehyde and an alcohol group. Similarly the cyclic structure of ketoses is hemiketal. Creation of anomeric carbon, generates new pair of isomers, the α and β configuration, that are anomers to each others. They differ in distribution of H and OH group around the asymmetric anomeric carbon atom C1 in aldoses or C2 in ketoses. CH2OH CH2OH O O OH H H H H H OH H OH H OH H OH OH H OH H OH -D-Glucose -D-Glucose Modified Fischer projection formula: In α - configuration the, the –OH on the anomeric carbon projects to the same side of the ring  The cyclic Hawroth α and β anomers projection formula:of a sugar in solution spontaneously (but In α slowly) form an equilibrium - configuration, mixture,carbon -OH of anomeric a processis known trans toasCH2OH mutarotation. glucose, the α-glucopyranose makes up 38% of the mixture while β – For(different) group & β-glucopyranose configuration, makes -OH of 62%anomeric carbon is cis to CH2OH (same) o the mixture.  EPIMERS They are isomers which differ in distribution of H and OH groups around a single asymmetric carbon atom other than the anomeric and DL-form creating carbon before the last i.e., without difference on other carbon atoms. Glucose and mannose are C2 epimers, while glucose and galactose are C4 epimers. CHO CHO CHO H C OH HO C H H C OH HO C H HO C H HO C H H C OH H C OH HO C H H C OH H C OH H C OH CH2OH CH2OH CH2OH Glucose Mannose Galactose Galactose and mannose are isomers rather than epimers because they differ in the position of –OH groups at two asymmetric carbons Ribose and arabinose are C2 epimers, while ribose and xylose are C3 epimers. CHO CHO CHO H C OH HO C H H C OH H C OH H C OH HO C H H C OH H C OH H C OH CH2OH CH2OH CH2OH Ribose Arabinose Xylose Arabinose and xylose are isomers rather than epimers because they differ in the position of –OH groups at two asymmetric carbons SUGAR DERIVATIVES 1. Sugar acids 2. Sugar alcohol 3. Amino sugars 4. Deoxy sugars  1.SUGAR CHO ACIDS COOH H C OH H C OH Aldonic acids: Produced by oxidation HO C H ofbromine carbonylwater, carbonO HO C H 2 to carboxylic group. H C OH H C OH Gluconic acid is formed fromH glucose C OHby the effect of H C OH glucose oxidase enzyme CH2OH CH2 OH D-Glucose D-Gluconic acid Clinical Correlates: The oxidation of glucose by glucose oxidase is a highly specific test for glucose used to measure the amount of glucose in urine and in blood using test strips.  CHO CHO 1.SUGAR H C ACIDS OH H C OH HO C H H2O2 HO C H Uronic acids: produced by oxidation H C OHof lastDil. hydroxy Nitric carbon acid H C OH to carboxylic group. H C OH H C OH D-Glucuronic acid from D-GlucoseCH2OH COOH D-Glucose D-Glucuronic acid CHO COOH H C OH H C OH Aldaric acids (Saccharic acid; HO C Dicarboxylic H acid): O HO C H 2 Produced by oxidation of both. H C OH Conc. Nitric acid H C OH e.g D-Glucaric acid from D-glucose H C OH H C OH N.B.: L-ascorbic acid (vit. C) is a sugar acid. CH2OH COOH D-Glucose D-Glucaric acid  2. Sugar alcohols (Alditols) Due to reduction of aldoses and ketoses at the carbonyl carbon. e.g.: Glucose → Sorbitol Mannose → Mannitol Fructose → Sorbitol and Mannitol  3-Amino sugars (hexosamines) : Replacing OH group on C2 by an amino group (NH2) produces them. Components of Glycoproteins, Glycolipids, and Glycosaminoglycans. D-Glucose to D- Glucosamine D-Galactose to D- Galactosamine  4-Deoxysugars: These are sugars in which OH group is replaced by H. At C2: deoxyribose that enters in structure of DNA. CHO CHO H C OH H C H H C OH H C OH H C OH H C OH CH2OH CH2OH Ribose Deoxyribose At C6: L-galactose gives L-fucose that enter the structure of glycoproteins  Disaccharides 1- Reducing Disaccharides It has a free aldehyde group (anomeric carbon) 2- Non-reducing Disaccharides: It has no free aldehyde group (anomeric carbon)  Reducing Disaccharides: The hydroxyl group of anomeric carbon is not linked to another compound by glycosidic bond. The sugar act as a reducing agent react with chromogenic agents (ex, Benedict agent) causing the reagent to be reduced and colored with aldehyde group becoming oxidized A-Maltose (malt sugar): It consists of 2 -glucose units linked by -1,4-glucosidic linkage. Give Glucose + glucose by maltase enzyme. CH2OH CH2OH O O H H OH..... H H H H 1 4 H OH H OH O H..... OH OH H OH H OH -Glucose Glucose − and  −Maltose  CH2OH O H H B-Isomaltose: OH H OH H 1 O H OH It is formed of 2 -glucose linked by -1,6-glycosidic linkage. -Glucose 6CH2 O OH..... H H H OH H OH H..... OH H OH Glucose − and −isomaltose CH2OH CH2OH O O C-Lactose (milk sugar): OH H OH..... H It is formed of -galactose and -glucose linked by -1,4- H 1 O 4 H H OH H glycosidic linkage H OH H H..... OH gives Glucose + galactose by lactase enzyme H OH H OH -Galactose Glucose − and −Lactose  Lactose Intolerance Symptoms: Bloating. Abdominal discomfort. diarrhea Cause ◦ Lactase deficiency Non-reducing Disaccharides: CH2OH O H H -Glucose H Sucrose (table sugar, cane sugar): OH OH H 1 H OH The 2 anomeric carbons (C1 of glucose and C2 of CH2OH O O fructose) are involved in the linkage, -1,2-glycosidic  -Fructose H OH 2 H CH2OH linkage(no free hydroxyl groups). OH H Sucrose give Glucose + fructose by sucrase enzyme. All monosaccharides are reducing sugars. All disaccharides (EXCEPT sucrose) are reducing sugars. Oligo- and polysaccharides are non-reducing sugars.  POLYSACCHARIDES They are condensation products of more than ten monosaccharide units. They may be linear or branched polymers. Can be classified as Composed of a single type Homopolysaccharide monosaccharide building block Examples: Starch, Glycogen, Cellulose. Composed of more than one type of Heteropolysaccharides monosaccharide building block Examples: Glycosaminoglycans A. STARCH: It is the stored form of carbohydrate of plants. It is present in cereals such as wheat, rice and potatoes. It is in the form of starch granules.The core of the granule is amylose (20%) and the shell is amylopectin (80%). Amylose Amylopectin Starch granule 1. Amylose:. Straight chain compound of α-glucose units linked by α-1,4-glucosidic bond. 2. Amylopectin: branched chains α-glucose units linked by α-1,4- glucosidic linkage along the branch and by α-1,6-glucosidic linkage at the branching point.  B. GLYCOGEN: It is the main storage carbohydrate of animals Its structure is similar to amylopectin a branched tree with α -1,4- glucosidic linkage along the branch and α-1,6-glucosidic linkage at the branching point. It is similar to starch, shorter, more branched and more water- soluble. It is mostly found in liver and muscle cells as granules. C. CELLULOSE: It is the major structural component of most plant cell walls. Polymer made from β-glucose units linked primarily between carbons 1 and 4 (similar to starch, but note that the β 1-4 linkage makes a huge difference). It is water-insoluble and indigestible as mammals lack any enzyme that hydrolyze β 1-4 linkage. It is the major food for herbivorous animal where it is fermented into short chain fatty acids.  Amylose of starch: Linear (not branched)  1-4 glycosidic bond  1-4 glycosidic bond cellulose  Heteropolysaccharide ⦁ Polysaccharides composed of more than one type of monosaccharide are termed heteropolysaccharides. ⦁ Glycosaminoglycans (mucopolysaccharides) are linear polymers of repeating disaccharides E.g, Heparin (anticoogulant), Hyluronic acid Keratan and Dermatan sulfate in extracellular matrix of connective tissue and synovial fluid.  ABO BLOOD TYPES  ABO blood types refer to carbohydrates (mucopolysaccharide) on red blood  These chemical markers are oligosaccharides that contain either three or four sugar units.  Sugar units are D-galactose, L-fucose, N-acetylglucosamine, and N-acetylgalactosamine.  Carbohydrates and Blood groups The following shows the carbohydrates and their attachments in type O, type A, and type B blood. Type AB blood has both type A and type B sets on their blood cells. COMPLEX CARBOHYDRATES Carbohydrates can be attached by glycosidic bonds to non-carbohydrate molecules including: 1- Purines and pyrimidines (in nucleic acids) 2- Proteins (in glycoproteins and proteoglycans) 3- Lipids (glycolipids) 4- Aromatic ring (in steroids and bilirubin)