Carbohydrates Chemistry PDF

Dr. Mohamed Ahmed Abdelmoneim Lecturer of Biochemistry Carbohydrates Chemistry  Objectives  Illustrate carbohydrates definition and functions.  Classify carbohydrates according to their structure.  Explain the characters and different types of monosacc...

Dr. Mohamed Ahmed Abdelmoneim Lecturer of Biochemistry Carbohydrates Chemistry  Objectives  Illustrate carbohydrates definition and functions.  Classify carbohydrates according to their structure.  Explain the characters and different types of monosaccharides.  Illustrate asymmetric carbon and isomerism.  Explain important sugar derivatives structure and functions.  Clarify the characters and types of disaccharides.  Demonstrate polysaccharides structure and functions.  Explicate complex carbohydrates, glycoproteins and proteoglycans.  Biochemistry The principal types of biological molecules (biomolecules) are: Macro molecules Micro molecules 1. Carbohydrates Vitamins 2. Lipids Minerals 3. Proteins 4. Nucleic acids 5. Enzymes [email protected] [email protected] www.su.edu.eg  Carbohydrates Carbohydrates are organic, polyhydroxy aldehydes, or ketones, derivatives. Biological importance of Carbohydrates Serve several biochemical functions: Major source of metabolic energy, both for plants and animals and represent 60% of our diet.  Used in the biosynthesis of: - Energy transport compound ATP. - Cell membrane - Cell receptors - RNA and DNA - Vitamins (B2 and C ) Form structural elements, such as chitin in animals and cellulose in plants. Form fibers that can help to lower blood glucose and cholesterol levels and prevent constipation.  Dietary sources of Carbohydrates Found in: Fruits Vegetables Legumes (beans, peas) Grains (wheat) Milk Soft drinks Corn  Classification of carbohydrates Based on the number of sugar units in total chain into: Monosaccharides: single sugar unit. Disaccharides: two sugar units. Oligosaccharides: 3 to 10 sugar units. Polysaccharides: more than 10 units.  Monosaccharides Single sugar unit, and simplest units of carbohydrate. Classification of monosaccharides: 1 2 A) According to the presence of aldehyde or ketone group. 1) Aldoses: contain an aldehyde group (CHO ). 2) Ketoses: contain ketone group ( C=O), a ketose can be indicated with the suffix ulose. B) According to the number of carbon atoms in the backbone: C3: Triose. C4: Tetrose. C5: Pentose. C6: Hexose. C) According to the presence of aldehyde or ketone group & number of carbon atoms. Aldoses Ketoses Trioses Glyceraldehyde Dihydroxy acetone (Aldotriose) (Ketotriose) Tetrose Erythrose (Aldotetrose) Erythulose (Ketotetrose) Pentoses Ribose, xylose, arabinose Ribulose, xylulose (Aldopentose) (Ketopentose) Hexoses Glucose, mannose, Fructose (Ketohexose) galactose (Aldohexose)  Biological importance of monosaccharides Ribose: is a component of RNA, ATP, GTP, NAD& FAD. Deoxyribose: is a component of DNA. Glucose: is the sugar of blood & is the important sugar of carbohydrates. Fructose (fruit sugar): is the main sugar of semen. Galactose: is synthesized in mammary gland to make the lactose of milk (milk sugar). Fructose & galactose are converted to glucose in liver. Mannose: is a constituent of many glycoproteins.  Asymmetric carbon (Chiral) Any carbon atom attached to four different atoms or groups. e.g. middle carbon of glyceraldehyde.  Isomerism It is the ability of substance to present in more than one form (isomers). Isomers have the same structural formula but differint structures Structural Sterioisomer Optical different in the spatial different in the order of cnfiguration attachment of atoms Enantiomers Diasteriomers nonsuperimposable mirror images non mirror images Epimers Anomers Any substance having asymmetric carbon (s) posses the following properties: 1. Optical activity: the ability of substance to rotate plane of polarized light either to right (d or +) or to left (l or -).  2. Stereoisomers CHO Compounds having the same structural formula but differing in spatial configuration. H C OH - Number of isomers= 2n where n is the number of CH2OH Glyceraldehyde asymmetric carbon. (reference sugar) Aldotriose.  A. Enantiomers: CHO CHO Are mirror images of each other that aren’t H C OH HO C H CH2OH CH2OH D-Glyceraldehyde L-Glyceraldehyde superimposable, in other words, the configuration OH group on sub-terminal OH group on sub-terminal carbon is written on right side. carbon is written on left side. at each chiral carbon is opposite.  D, L configurations Are related to OH attached to sub terminal asymmetric carbon if OH in the right side (D form), if OH in the left side (L form). Most of the monosaccharides occurring in mammals are of D form.  B. Diasteriomers Are defined as non-mirror image non-identical stereoisomers. Hence, they occur when stereoisomers of a compound have different configurations at stereo-centers (Chiral) and are not mirror images of each other. One carbon different includes: Epimers. Anomers.  Epimers They are stereoisomers that differ in the position of hydroxyl group at only one a symmetric carbon (epimeric carbon). Examples D-glucose and D-galactose are epimers at C4. D-glucose and D-mannose are epimers at C2.  1 CHO Smallest monosaccharide aldose is glyceraldehyde H C OH (Reference sugar). CH2OH Smallest monosaccharide ketose is dihydroxyacetone. CH2OH C O2 CH2OH  Ring structure of monosaccharaides furan pyran There are two forms of ring form: 1- Pyranose ring: includes 5 carbons. 2- Furanose ring: includes 4 carbons. Cyclic structure in Haworth formula, the OH group in the right side of old ring (Fischer) written downwards in Haworth and the OH group in the left side of old ring written upwards in Haworth. N.B Down right, up left Glucose in solution present (99%) in glucopyranose & 1% glucofuranose. 99% of glucopyranose (36%) α, D form & (63%) B, D form. In ketohexoses: e.g. fructose Furanose ring occurs between C2+ C5  Anomeric carbon (α & B configuration) It is the asymmetric carbon atom obtained from active carbonyl sugar group. Carbon number 1 in aldoses and carbon number 2 in ketoses. Anomers: are isomers obtained from the change of position of hydroxyl group attached to the anomeric carbon e.g. α and β glucose are 2 anomers. Also, α and β fructose are 2 anomers. 1. Study the following Fischer projections to answer the questions below. A. Is galactose a D-sugar or an L-sugar? B. Is mannose a D-sugar or an L-sugar? C. Choose either one, and sketch it as it would appear if it was an L-sugar. D. Are these two carbohydrates enantiomers? If not, in how many places do they differ? E. What is the term to describe the relationship between galactose and mannose? 3. Examine the following Haworth projections to answer the questions below. 1.Circle each anomeric carbon 2.Which of the two is the alpha anomer and which is the beta anomer? 3.Are these structures considered enantiomers or anomers? 4.Are these monosaccharides reducing sugars? Explain. 5.Can you convert the alpha anomer to a beta anomer? Explain. 13. Study these Haworth projections to answer the following for each of them. 1. Is it a furanose or a pyranose? 2. Is it an alpha or beta anomer? 3. Circle the anomeric carbon.  Monosaccharide derivatives 1. Sugar acids Aldoses may be oxidized to 3 types of acids A. Aldonic acid: aldehyde group is oxidized to a carboxyl group, e.g. glucose (gluconic). B. Uronic acid: aldehyde is left intact and primary alcohol at the other end is oxidized to COOH, e.g. glucose (glucuronic). C. Aldaric acid: aldehyde and last hydroxyl carbon are oxidized to COOH, e.g. glucose (glucaric).  Sugar acids CHO CHO CHO COOH H C OH H C OH H C OH H C OH HO C H bromine water, O2 HO C H HO C H H2O2 HO C H H C OH H C OH H C OH Dil. Nitric acid H C OH H C OH H C OH H C OH H C OH CH2OH CH2OH CH2OH COOH D-Glucose D-Gluconic acid 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 CH2OH COOH D-Glucose D-Glucaric acid Importance of glucuronic acid: Glucuronic acid is often linked to xenobiotic substances such as drugs, pollutants. Conjugation with bilirubin, and steroid hormones. Formation of glycosaminoglycans.  2- Deoxy Sugars CHO CHO They are produced by replacing OH group on by H C OH H C H H C OH H C OH hydrogen atom i.e. one oxygen missed. H C OH H C OH CH2OH CH2OH Ribose Deoxyribose At C2: deoxyribose that enters in structure of DNA.  3- Amino Sugars They are produced by replacing OH group on C2 by an amino group (NH2) or acetyl amino group. Examples: CH2OH CH2OH 6 CH2O-SO3H Glucosamine: it occurs in heparin & hyaluronic H O H H O H H O H H H H H OH H OH H OH 2 OH OH 2 OH 2 OH OH OH acid. H NH2 H HN C CH3 H NH-SO3H O -D-glucoamine N-acetyl-glucosamine sulfated glucosamine Galactosamine: it occurs in chondroitin sulphate. Importance of amino sugars Formation of glycoprotein, proteoglycan and gangliosides. Some antibiotics contain amino sugar such as erythromycin.  Glycosidic bond It is the bond between a carbohydrate & other compound to form complex carbohydrate. This bond is between OH of anomeric carbon and another compound which may be:. Glycone: sugar unite (disaccharide glycosides). Aglycone: non carbohydrate to form glycoside.  Glycosides These are compounds resulting from condensation between monosaccharides and other compounds. Examples of glycosides: Disaccharides. Sugar nucleotides. Some antibiotics e.g. streptomycin. Cardiac glycosides (Digitalis).  Disaccharides Two monosaccharides linked by glycosidic linkage. Examples : 1- Maltose: 2 -glucose ( 1-4 g.b) (maltase) RS. 2- Isomaltose: 2 -glucose ( 1-6 g.b) RS. 3- Lactose: β-glucose + β-galactose (β 1-4 g.b) (lactase) RS. 4- Sucrose: -glucose + β-fructose (1-β2 g.b) (sucrase) NRS.  Maltose Also named malt sugar, or corn sugar. Composed of two 2 – D- glucose molecules linked by a -1-4 glycosidic bond. Cleavage (digestion) by maltase enzyme. Contain free aldehyde group so has the same properties as monosaccharides (Reducing sugar).  Isomaltose - Like Maltose It is composed of two 2  –D -glucose molecules but linked by a -1,6-glycosidic bond. - Cleavage (digestion) of maltose by isomaltase enzyme. - (Reducing sugar).  Lactose Milk sugar. Formed of β -glucose and β-galactose linked by β 1-4 glycosidic linkage. Non fermentable sugar. Cleavage (digestion) of lactose by lactase enzyme. Reducing sugar.  Sucrose Cane sugar or table sugar. Formed of α-glucose & β-fructose linked by (α1- β2 glycosidic linkage). Cleavage (digestion) by sucrase (invertase) enzyme. Non reducing sugar. All monosaccharides are reducing sugars. All disaccharides (EXCEPT sucrose) are reducing sugars. Oligo- and polysaccharides are non-reducing sugars.  Polysaccharides They are Composed of more than 10 monosaccharide units linked by glycosidic bond. They are of 2 types : A. Homopolysaccharides. B. Heteropolysaccharides.  A. Homopolysaccharides These are composed of repeated units of similar monosaccharide. It include: 1. Starch. 2. Glycogen 3. Cellulose. 4. Inulin  1. Starch (glucosan or glucan) It is formed of α-glucose units linked by α-1,4 glycosidic bonds with few branches at α-1,6 glycosidic bonds. Starch granules Consist of: Amylose Amylopectin A) Amylose(15-20%) It represents the inner part of starch. It formed of non branching structure of glucose units linked together by α-1,4 glycosidic bonds. B) Amylopectin (80-85%) It represents the outer part of starch Each chain of amylopectin is composed branched chain of 24-30 glucose units linked together by α-1,4 glycosidic bonds at along the chain and α-1,6 glycosidic bonds at branched points.  2. Glycogen (Animal starch) Major storage form of carbohydrates in animals. It is a highly branched chain homopolysaccharide. Present mainly in muscle and liver. Formed of α-glucose units linked by α-1,4 glycosidic bonds with many branches at α-1,6 glycosidic bonds. Same structure as starch (branches 12-14 sugar units).  3. Cellulose Forms the wall of plant cells. Formed of straight chain of β-glucose units linked by β-1,4 glycosidic bonds with no branches. properties Not digested in human body due to the absence of hydrolytic enzymes (cellulase) that attack β-link, but it prevents constipation.  4. Inulin Formed from repeated units of (- D- fructose) linked by ( 1-2) bonds. It is not digested by humans. It is important in determining the glomerular filtration rate (GFR).  B. Heteropolysaccharides Formed of different sugar units. 1. Pectins: Esterified D-galacturonic acid resides in α-(1-4) chain. Pectins are found in the fruits (citrus, apples, apricots). Function: used as gelling agents, so used in treatment of infantile diarrhea.  2. Glycosaminoglycans (Mucopolysaccharides) repeated disaccharides units (sugar acid as glucuronic acid + amino sugar glucosamine or galactosamine or acetylated form). properties 1-They are present extracellular except heparin. 2-They are structural component of connective tissue. 3-They act as a lubricant e.g. synovial fluid and vitreous humor. 4- highly compressible.  A-Hyaluronic acid repeated disaccharide units, composed of β glucuronic acid and β N-acetylglucosamine. Hyaluronic acid is sulfate free. Site Synovial fluid Vitreous humor of the eye Embryonic tissue Cartilage Function of Hyaluronic acid: 1- Gel made of hyaluronic acid has good resistance to compression ,thus it acts as a lubricant and shock absorber. 2- permit cell migration during wound repair or morphogenesis. 3- It makes extracellular matrix loose because of its ability to attract water. Hyaluronidase enzyme: This enzyme hydrolyses hyaluronic acid.It is secreted by invasive bacteria. It helps the spread of bacteria through subcutaneous tissue. It is also present in sperm and helps fertilization.  B- Chondroitin sulfate Structure: Glucuronic acid + N-acetylgalactosamine+ sulfate. Site: Cartilages, Tendons, Ligaments, Cornea ,Umbilical cord, Skin and aorta. Function: 1- Binding of collagen of cartilage. 2. Maintained the shape of skeletal system 3- Compressibility of cartilage.  C- Keratan sulfate Structure: repeated disaccharides (galactose) no uronic acid + N-acetylglucosamine+ sulfate. Site: Cornea and proteoglycan of cartilage. Function: Play an important role in corneal transparency  D- Dermatan sulfate Structure: repeated disaccharides iduronic acid + N-acetylgalactosamine+ sulfate. Site: Cornea, sclera, skin, blood vessels and heart valves. Function: In cornea: Play a role with keratin sulphate in corneal transparency. In sclera: play a role in maintaining the overall shape of the eye.  E- Heparin Structure: repeated disaccharides iduronic acid + glucosamine+ sulfate. CH2OSO3H COOH H O O H H H Site: mast cells located along the wall of blood OH H OH O O O vessels of liver, lung, skin, heart and kidney. H OSO3H H NHSO3H Function: It is an anticoagulant produced by the mast cells of the liver.  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).  3- Glycoproteins & proteoglycans Glycoproteins Proteoglycans Main component Primarily protein + some carb. Primarily carb.+ some protein. Carbohydrate Content 10-15% 50-60% Carbohydrate Component oligosaccharides glycosaminoglycans Type of sugar No uronic acid uronic acid Sulfate group No yes Shape of carbohydrates Usually branched Linear, unbranched Examples Collagens, mucins, transferrin, Chondroitin sulfate, dermatan sulfate, immunoglobulins, others heparan sulfate, keratan sulfate, others Functions Extracellular matrix Ground substance and supporting Blood group antigens. tissues as bones , cartilage and Cell receptors tendons. Plasma proteins Cell membrane Hormones, enzyme & Ig  THANK YOU For any questions feel free to contact me by 01147996609