Carbohydrates PDF

12/8/2024 Carbohydrates 1 Carbohydrates importance Carbohydrates are the most abundant organic molecules in nature. They have a wide range of function, including providing a significant fraction of energy in the body, and serving as cell m...

12/8/2024 Carbohydrates 1 Carbohydrates importance Carbohydrates are the most abundant organic molecules in nature. They have a wide range of function, including providing a significant fraction of energy in the body, and serving as cell membrane components. Carbohydrates also serve as a structural component of many organisms: The cell walls of many bacteria.(PEPTIDOGLYCAN) The exoskeleton of many insects. (CHITIN) The fibrous cellulose of plants. (CELL WALL) 2 1  12/8/2024 Classification of sacchrides 1-According to the number of carbon atoms. 2. According to the number of saccharic units 3 1. According to the number of carbon atoms > Monosaccharides are also classified according to the number of carbon atoms they contain: (trioses), (tetroses), (pentoses), (hexoses), (heptoses) 4 2  12/8/2024 According to the number Of saccharic units 1 – Monosaccharides : Aldoses : Glucose - Ribose. Ketoses : Fructose. 2 – Disaccharides : Sucrose , Maltose , Lactose. 3 - Polysaccarides : a – Oligosaccarides : > 3 – 10 unite of saccharic unite # Raffinose (3 unit) b – Polysaccharides : 1 – Homoglucan : Starch , Glucogen. 2 – Heteroglucan : Hyalaronic , Chondrantin. Heparin 4. Derived carbohydrates – sugar acids, sugar alcohols, deoxysugars, and sugar amines 5 Monosaccharides Monosaccharides has the general formula (CH2O)6 and contains either an Active aldehyde group (aldose) or active ketone group (ketose) The simplest sugars with 3 carbon atoms are called trioses. Trioses either aldotriose as Glyceraldehyde or Ketotriose as Dihydroxyacetone 6 3  12/8/2024 Classification of Monosaccharides based on their spatial orientation (stereochemistry). A monosaccharide can be classified as a D or L isomer, depending on the spatial orientation of the –H and –OH groups attached to the carbon atom adjacent to the terminal primary alcohol group. The D isomer is represented when the –OH is written to the right of this carbon in the Fischer projection formula. The L isomer is represented when this –OH is written to the left. 7 ALDOSE SUGER 8 4  12/8/2024 KETON SUGER 9 10 5  12/8/2024 Isomers: Compounds that have the same chemical formula but have different structures are called isomers.  Ex: fructose, glucose, manose, and galactose are all isomers of each other, having the same chemical formula: C6 H12 O6 11 Epimers Carbohydrates isomers that differ in configuration around only one specific carbon atom. o Galactose and Glucose are C-4 epimers: Their structures differ only in the position of the OH group at carbon 4. o Glucose and mannose are C - 2 epimers. 12 6  12/8/2024 Enantiomers A special type of isomerism is found in the pairs of structures that are mirror images of each other. These mirror images are called enantiomers D & L-sugar. 13 The majority of the sugars in human are D-sugars. Racemases Enzymes are able to interconvert L- and D- isomers. 14 7  12/8/2024 The reaction of an alcohol with an aldehyde (hemiacetal), or with a ketone hemiketal 15 Cyclization of Monosaccharides D-glucose exists in three different forms: The open-chain form, and two cyclic forms:  1 - α-D-glucopyranose  2 - β-D-glucopyranose 16 8  12/8/2024 Cyclization of the Open-chain form of D- glucose Tetroses and larger sugars can cyclize by reaction of the aldehyde or ketone group on anther carbon atom of the sugar. – Glucose mainly cyclize to form a six-membered pyranose ring – Fructose form five-membered furanose ring. 17 Haworth projection formula Anomers of D- glucopyranose exist, depending on whether the hydroxyl group attached to the carbon atom C1: below the plane of the ring (the alpha form ) above the plane of the ring ( beta form ) 18 9  12/8/2024 19 Enzymes are able to distinguish between these two structures and use one or the other preferentially > For example, glycogen is synthesized from α-D- glucopyranose, whereas cellulose is synthesized from β-D- glucopyranose 20 10  12/8/2024 Haworth projection formula 1 CH2OH 2 c O 6 1 3 HO c H HOH2C OH CH2OH HOH2C O CH2OH 5 2 4 H c OH c H HO c H HO H OH 5 H c OH c c O 4 3 H OH H 6 CH2OH OH H (α ) -D-Fructofuranose D-Fructose (A ring from of fructose) Anomeric carbon New asymmetric center 21 Cyclization of the Open- chain form of D- glucose 22 11  12/8/2024 Anomeric carbon : the most oxidized carbon (the one attached to two oxygen atoms. Two configurations α β 23 DISACCHARIDES A disaccharide is formed when two monosaccharides become joined by a glycosidic bond. The bond may be an alpha or beta bond depending on the configuration of the anomeric carbon atom involved in the bond. 24 12  12/8/2024 Reducing and Nonreducing Sugar Usually, the anomeric carbon atom of only one of the two monosaccharides is involved in the bond so that the disaccharide still has one free aldehyde or ketone group and still reducing. However, in sucrose both anomeric carbon atoms are bonded together so that sucrose is a non-reducing disaccharide. 25 Naming Glycosidic Bonds 26 13  12/8/2024 27 Disacchrides Disacchrides are formed when the anomeric carbon of one sugar molecule interact with one of several OH groups in the other sugar molecule. 1. Maltose: polymer of glucose resides α(1→4) 2. Cellobiose: consists of two glucose molecules linked by a β (1→4) bond 1. Lactose : galactose + glucose. β (1→4) 2. Sucrose: glucose + fructose. α(1→4) 28 14  12/8/2024 Lactose Maltose Sucrose 29 Oligosaccarides Consist of 3 – 10 unite of saccharic unite. eg. Raffinose. 30 15  12/8/2024 General Characteristics of Polysaccharides Alternate name is glycan Consist from more than 10 units of 4. Homopolysaccharides monosaccharidse, joined together by – starch glycosidic bonds. – glycogen Not sweet and don’t show positive tests – cellulose with Tollen’s and Benedict’s solutions – chitin Limited water solubility 5. Heteropolysaccharides Classified as – hyaluronic acid 1. Storage polysaccharides: starch, – heparin glycogen – chondroitin sulfate 2. Structural polysaccharides: cellulose, Chitin 3. Acidic polysaccharides : heparin, hyaluronic acid 31 Types of Polysaccharidse Polysaccharidse or glucans are two types: 1 –Homo-polysaccharides: Homoglucan. 2 – Hetero-polysaccharidse: Heteroglucan. 32 16  12/8/2024 HOMO-POLYSACCHARIDES: Homoglucan Homopolysaccharides are those Carbohydrates which on hydrolysis give the same type of Monosacchreidse units. The major members of homopolysaccharides are:  Glycogen, Starch, Cellulose, Inulin Dextran. 33 34 17  12/8/2024 Storage polysaccharides: Starch & Glycogen Starch is – the most common storage homoglycan of Glucose in plants and glycogen in animals. – Starch is present as a mixture of amylose & amylopectin. (α- amylase, debranching enzyme). Glycogen – contains the same types of linkages found in amylopectin, – the branches are smaller and more frequent occurring every 9 to 12. – It is larger than the starch molecules (50 000) 35 Structure of amylose (a) Structure of amylose. Amylose, one form of starch, is a linear polymer of glucose residues linked by (1-->4)-D-glucosidic bonds. 36 18  12/8/2024 Structure of amylopectin Amylopectin, a second form of starch, is a branched polymer. The linear glucose residues of the main chain and the side chains of amylopectin are linked by (1-->4)-D-glucosidic bonds, and the side chains are linked to the main chain by (1-->6)-D-glucosidic bonds. 37 STARCH→↓ MALTOSE→↓ GLUCOSE Amylase Maltase amylopectin 38 19  12/8/2024 Structural Polysaccharides 1. Cellulose Yields D-glucose upon hydrolysis yet man & the carnivorous animals can’t utilize cellulose as a source of glucose. Human‘s digestive juices lack the enzyme cellulase that hydrolyze - 1,4- glucosidic linkages. Ruminants (cows, goats) and termites have, within their digestive tracts, microorganisms that produce cellulase 39 39 Structural Polysaccharides Chitin Similar to cellulose in both function and structure Polymer of N-acetyl-D- glucosamine bound by β-1  4 glycosidic linkages (has a linear extended structure like cellulose) Function is to give rigidity to the exoskeletons of crabs, lobsters, shrimp, insects, and other arthropods 40 40 20  12/8/2024 Complex Carbohydrates Carbohydrates can be attached by glycosidic bonds to non-carbohydrate structures, including: - Purine and pyrimidine bases. - Aromatic rings (steroids and bilirubin). - Proteins (glycoproteins). - Lipids (glycolipids). 41 N- and O-glycosides If the group on the non-carbohydrate molecule to which the sugar is attached is an – NH2 group, the structure is an N- glycoside and the bond is called an N- glycosidic link. If the group is an –OH, the structure is an O-glycoside and the bond is an O-glycosidic link. 42 21  12/8/2024 Hetero-polysaccharidse (Heteroglucan) Heteroglucan are those Carbohydrates which on hydrolysis yield different sugars or their derivatives. like glucouronic acid, amines, alcohol, sulphuric acid. Examples: – Hyaluronic Acid, – Chondroitin Sulphates, – Heparin, Keratin Sulphates – Dermatan Sulphates 43 Glycosaminoglycans,, and Glycoproteins Glycosaminoglycans (GAGs) are large complexes of negatively charged hetero -polysaccharide chains. Glycosaminoglycans have the special ability to bind large amounts of water, thereby producing the gel-like matrix that forms the basis of the body’s ground substance, which, along with fibrous structural proteins such as collagen and elastin. 44 22  12/8/2024 Glycosaminoglycans (GAGs) composed of repeating: [acidic sugar-amino sugar]n disaccharide units. 45 Proteoglycans They are generally Glycosaminoglycans associated with a small amount of protein, forming proteoglycans, which typically consist of over 95% carbohydrate. Proteoglycans consist of a core protein to which long, unbranched, glycosaminoglycan chains are attached. Structure of proteoglycans All of the glycosaminoglycans, except hyaluronic acid, are found covalently attached to protein, forming proteoglycan monomers. Proteoglycan aggregates: The proteoglycan monomers associate with a molecule of hyaluronic acid to form proteoglycan aggregates. The association is not covalent, but occurs primarily through ionic interactions between the core protein and the hyaluronic acid. The association is stabilized by additional small proteins called link proteins 46 23  12/8/2024 Examples of proteoglycan: 1. Hyaluronic Acid Structures: Consist of repeating units of D- glucouronic acid and N-acetyl-glucosamine. Locations and functions: It present in the synovial fluid of joints and acts as a lubricant and shock absorbent. It also present in the skin, and in vitreous humor of the eye. It form a protective covering around ovum. Hyaluronidase enzyme which present in semen plays an important role in fertilization by acting on hyaluronic acid present in covering of ovum 47 Examples of proteoglycan: 2. Chondroitin Sulphates Chondroitin sulphates consist of repeating units of: – N-acetylgalactosamine and glucouronic acid. Most abundant GAGs in the body Chondroitin sulphates are present in various tissues as cartilages, skin, tendons, bones, cornea and heart valves. 48 24  12/8/2024 Examples of proteoglycan: 3. Heparin Heparin contains repeating units of sulphated glucosamine and sulphated glucouronic acid. Heparin act as anticoagulant and present in liver, lungs, thymus, spleen and blood. 49 Glycoproteins They are proteins to which oligosaccharides are covalently attached Glycoproteins contain highly variable amounts of carbohydrate. For example, immunoglobulin IgG, contains less than 4% of its mass as carbohydrate, whereas human gastric glycoprotein (mucins) contains more than 80% carbohydrate. 50 25  12/8/2024 Membrane-bound glycoproteins participate in a broad range of cellular phenomena, including  Cell surface recognition (by other cells, hormones, and viruses),  Cell surface antigenicity (such as the blood group antigens), and  As components of the extracellular matrix and of the  Mucins of the gastrointestinal and urogenital tracts, where they act as protective biologic lubricants.  All of the globular proteins present in human plasma are glycoproteins. 51 26