L12a Carbohydrates PDF

Carbohydrates Mokrish Ajat Dept. of Veterinary Preclinical Sciences Faculty of Veterinary Medicine UPM [email protected] VPP3021 Veterinary Biochemistry  To be...

Carbohydrates Mokrish Ajat Dept. of Veterinary Preclinical Sciences Faculty of Veterinary Medicine UPM [email protected] VPP3021 Veterinary Biochemistry  To be discussed Introduction and general functions Monosacchrides - classification - sugar derivatives Polysaccharides - carbohydrate analysis - disaccharides - structural polysaccharides - storage polysaccharides - glycosaminoglycans Glycoproteins - proteoglycans - bacterial cell walls - glycoprotein structure and function - glycomics VPP3021 Veterinary Biochemistry  Introduction Carbohydrates or saccharides (Greek: sakcharon – sugar) ‘hydrated carbon’ – (CH2O)n where n³3. Basic units – monosaccharides Sources Gluconeogenesis Photosynthesis (light processed combination of CO2 and H2O)- plant and bacteria VPP3021 Veterinary Biochemistry  General Functions An important source of C for the synthesis of other compounds and of chemical energy for immediate release Source of energy for human, most animal and microorganism Serves as temporary stores of glucose (glycogen, starch) As structural and supportive elements in the cell walls of bacteria, plants, in the connective tissues and cell oats of animal organism (eg. chitin, cellulose) VPP3021 Veterinary Biochemistry  General Functions Components of cell membranes Connective tissue eg. Glygosaminoglycans Antigenicity i.e. tissue types Anticoagulant eg. heparin Monosaccharide- principle components of nucleic acid (DNA and RNA) Serve to lubricate skeletal joints, to provide adhesion between cells. VPP3021 Veterinary Biochemistry  Monosaccharides - classification ¢ Monosaccharide ¢ Classified based of carbonyl group and number of C atoms ¢ Unbranched, single bonded carbon chain ¢ One of the carbon atom is double-bonded to an oxygen atom (carbonyl), each of the other carbon atoms has a hydroxyl group ¢ Carbonyl group, single unit polyhdroxy aldehyde (aldose) = glucose ¢ Carbonyl group, single unit ketone (ketose) - ribulose ¢ The most abundant – D-glucose (others, fructose and galactose ALDOSE KETOSE CHO CH2OH CHOH C O CH2OH CH2OH Glyceraldehyde Dihydroxyacetone (an aldotriose) (a ketotriose) VPP3021 Veterinary Biochemistry  Monosaccharides are classified by the number of carbon atoms they contain CnH2nOn. Name Formula triose C 3H 6 O 3 tetrose C 4H O 8 4 pentose C 5 H 10 O 5 hexose C 6 H 12 O 6 heptose C H O 7 14 7 octose C 8 H 16 O 8 VPP3021 Veterinary Biochemistry  Carbons Category Name Relevant examples 3 Triose Glyceraldehyde (aldotriose), Dihydroxyacetone (ketotriose) 4 Tetrose D-Erythrose (aldotetrose), Erythrulose (ketotetrose) 5 Pentose D- Arabinose, D-Xylose, D-Ribose, 2-D-Deoxyribose (aldopentose) D-ribulose (ketopentose) 6 Hexose D-Glucose, D-Galactose,D- Mannose (aldohexose), D-Fructose (ketohexose) 7 Heptose D-Sedoheptulose 9 Nonose Neuraminic acid also called sialic acid VPP3021 Veterinary Biochemistry  Monosaccharides Metabolic role Glyceraldehyde (aldose) Glu-3-P and Glu-1-P Dihydroxyacetone (ketone) are intermediate in glycolysis D-erythrose Glu-4-P is intermediate in Carb Met D-arabinose cell walls D-ribose RNA 2-D-deoxyribose DNA VPP3021 Veterinary Biochemistry  Monosaccharides role D-glucose Major energy source Sugar of blood Sugar of grape D-fructose Principle sugar of semen Sugar of fetal blood Sugar of fruits and honey D-galactose Sugar of Milk D-mannose Composition of mucopolysaccharides D-sedoheptulose Intermediate in calvin cycle VPP3021 Veterinary Biochemistry  Biologically most common aldoses are boxed VPP3021 Veterinary Biochemistry  Biologically most common ketoses are boxed VPP3021 Veterinary Biochemistry  Cyclization reactions for hexoses VPP3021 Veterinary Biochemistry  Sugar derivatives D-gluconic acid D-glucuronic acid D-glucitol Sorbitol Ascorbic acid Ribitol Myo-Inositol Xylitol Β-D-2-deoxyribose D-Glucosamine D-Galactosamine Please read from text book and expand this note VPP3021 Veterinary Biochemistry VPP3021 Veterinary Biochemistry  Vitamin C – A monosaccharide? Vitamin C, vital for life is a necessary part of our diet because we cannot synthesize it. (Most plants and animals except primates and guinea pigs can make their own Vitamin C). It is needed to maintain health of dentine, cartilage, connective tissue and bone Lack in diet may cause scurvy – impairment of collagen formation Recommended daily allowance ~45mg for adults (60mg if pregnant, 80mg if lactating). VPP3021 Veterinary Biochemistry  Polysaccharides – carbohydrate analysis Please read page 366, chapter 11, Biochemistry 4th edition Voet VPP3021 Veterinary Biochemistry  Glucose Assay ¢ The analytical procedure most often performed in the clinical chemistry laboratory is the determination of glucose in blood, urine, or other biological fluid — this need stems from the high incidence of diabetes in the population VPP3021 Veterinary Biochemistry  Glucose Assay Type 1 ¢ One of the first widely used methods was based on the fact that glucose reacts with 2- methylaniline (o-toluidine) in the presence of acetic acid to give an imine which has a blue- green color with an absorption max in the visible spectrum at 625 nm — the intensity of the absorption at 625 nm is proportional to the glucose concentration VPP3021 Veterinary Biochemistry  ¢ Blood glucose test for diabetics — Based on reaction of o-toluidine with glucose H3C CHO CH N H OH H3C H OH HO H HO H H2N H OH H OH H OH H OH CH2OH CH2OH VPP3021 Veterinary Biochemistry  Glucose Assay Type 2 — the enzyme glucose oxidase is specific for b-D-glucose — molecular oxygen, O2, used in this reaction is reduced to hydrogen peroxide H2O2 — the concentration of H2O2 is determined experimentally, and is proportional to the concentration of glucose in the sample CH2OH HO O HO OH + O2 + H2O OH b-D-Glucopyranose CO2H glucose oxidase H OH HO H H OH + H2O2 H OH Hydrogen peroxide CH2OH D-gluconic acid VPP3021 Veterinary Biochemistry  Glycosidic/glycoside bonds Glycoside: When monosaccharides link together, the linkage is called a glycosidic linkage. A monosaccharide hemiacetal can react with a second molecule of an alcohol to form an acetal O CH3OH O OH H+ OCH3 A ‘glycoside’ bond VPP3021 Veterinary Biochemistry  ¢ Glycosides are named by listing the name of the alkyl or aryl group attached to oxygen followed by the name of the carbohydrate with the ending -e replaced by -ide — b-D-glucopyranoside — a-D-ribofuranoside VPP3021 Veterinary Biochemistry  Dissacharides ¢ In most disaccharides the chemical bond that joins the two monosaccharide units – glycosidic bond that formed when the hydroxy group on one of the sugars reacts with the anomeric carbon on the second sugar. ¢ Glycosidic bond – readily hydrolyzed by acid but resist cleavage by base Abundant in nature: ¢ Sucrose (table sugar, cane sugar, saccharose, or beet sugar), ¢ lactose (milk sugar) ¢ maltose. Others: trehalose, cellobiose, lactulose, kojibiose, nigerose, isomaltose, sophorose, laminaribiose, gentiobiose, maltulose VPP3021 Veterinary Biochemistry  Maltose The major degradation product of starch, is composed of 2 glucose monomers in an α-(1,4) glycosidic bond. From malt, the juice of sprouted barley and other cereal grains. a-1,4-glycoside bond VPP3021 Veterinary Biochemistry VPP3020  Lactose is found exclusively in the milk of mammals and consists of galactose and glucose in a b-(1®4) glycosidic bond. The principle sugar present in milk — about 5% - 8% in human milk, 4% - 5% in cow’s milk b-1,4-glycoside bond VPP3021 Veterinary Biochemistry  Sucrose Prevalent in sugar cane and sugar beets, is composed of glucose and fructose through an a-(1®2)b-glycosidic bond. a-1,2-glycoside bond VPP3021 Veterinary Biochemistry VPP3021 Veterinary Biochemistry  Polysaccharide ¢ Most of the carbohydrates found in nature occur as polysaccharides of high molecular weight ¢ Some serve as storage forms of monosaccharides but some serve as structural elements in cell walls and connective tissues ¢ The monomeric building blocks used to generate polysaccharides can be varied but the predominant monosaccharide found is D- glucose. VPP3021 Veterinary Biochemistry  Two types of polysaccharides ¢ Homopolysaccharides — Contains only a single type of monomeric unit eg. starch (contains only D- glucose), glycogen and cellulose ¢ Heteropolysaccharides — Contains two or more different kinds of monomeric unit eg. hyaluronic acid of connective tissue VPP3021 Veterinary Biochemistry  Structural Polysaccharides Cellulose Chitin VPP3021 Veterinary Biochemistry  β-1,4-glycoside bonds Cellulose Cellulose is the most abundant structural polysaccharide Liner, unbranched homopolysaccharide of D-Glucose units joined by b(1®4) glycosidic bonds It has an average molecular weight of 400,000 corresponding to approximately 2800 D-glucose units per molecule Plant cell walls Maintains shape Withstands osmotic pressure changes VPP3021 Veterinary Biochemistry  Chitin Chitin (invertebrate exoskeleton)- b(1®4) linked N- acetylglucosamine polymer Therefore, like cellulose except N-acetyl group at C-2 in residue. Chitin: is an important structural polysaccharide of invertebrates. Eg in exoskeletons of insects Cell walls of fungi and algae are also a polymer of N- acetylglucosamine with b(1®4) linkages (very strong) VPP3021 Veterinary Biochemistry  Storage Polysaccharides Starch Glycogen VPP3021 Veterinary Biochemistry  Starch Used for energy storage in plant Insoluble in water Abundant in tubers eg. potatoes and seed eg. corn Contain 2 types of glucose polymer a-amylose (15-20%) Amylopectin (80-85% VPP3021 Veterinary Biochemistry  α-amylose Consists of long, unbranched chains of D- glucose units connected by a(1®4)linkages Such chains vary in molecular weight from a few thousand to 500,000 VPP3021 Veterinary Biochemistry  Amylopectin Also has a high molecular weight but is highly branched Chains consist of 24-30 units of D-glucose joined by a(1®4) glycoside bonds and branches created by a(1®6) glycoside bonds VPP3021 Veterinary Biochemistry  Starch Digestion Digestion of starch the main carbohydrate source in mammalian diet, begins in mouth Saliva contains an amylase which randomly hydrolyze the a-1,4-glycoside bonds Further hydrolysis of a- glucosidase And by debranching enzyme VPP3021 Veterinary Biochemistry  Glycogen The main storage polysaccharide of animal cells analogue of starch and is commonly referred to as animal starch, having a similar structure to amylopectin Primary structure of glycogen resembles that of amylopectin but glycogen is more highly branched with branch points occurring every 8 to 14 glucose residues VPP3021 Veterinary Biochemistry  Glycogen made primarily by the liver and the muscles, Abundant in liver (up to 7% of the wet weight) Muscles (1-2% of the muscle mass) can also be made by glycogenesis within the brain and stomach the amount of glycogen stored in the body, especially within the red blood cells, liver & muscles, mostly depends on physical training, basal metabolic rate and eating habits such as intermittent fasting. Small amounts of glycogen are found in the kidneys even smaller amounts in certain glial cells in the brain and white blood cells. The uterus also stores glycogen during pregnancy to nourish the embryo. VPP3021 Veterinary Biochemistry  It is a homopolymer of glucose in a a(1®4) linkage: it is also highly branched, with a(1®6) branch linkages occuring every 8-10 residues Very compact structure results from the coiling of the polymer chains. This compactness allows large amounts of carbon energy to be stored in small volume with little effect on cellular osmolarity VPP3021 Veterinary Biochemistry  Glycogen Storage Disease Caused by defects in glycogen synthesis and inability to breakdown glycogen for usage May caused by genetic disorder or acquired VPP3021 Veterinary Biochemistry  Heteropolysaccharides Polysaccharides composed of two or more types of monosaccharide units The most abundant heteropolysaccharides in the body are the glycosaminoglycans (GAGs). Many are heteropolysaccharide linked to proteins and these are known as proteoglycans VPP3021 Veterinary Biochemistry  GAGs - Structure Glycosaminoglycans are long unbranched polysaccharides containing a repeating disaccharide unit with negatively charged groups The disaccharide units contain either of two modified sugars: N- acetylgalactosamin e (GalNAc) or N- acetylglucosamine (GlcNAc) and a uronic acid such as glucuronate or iduronate VPP3021 Veterinary Biochemistry  GAGs – Location and function usually found in extracellular space in multicellular organisms – to produce a viscous extracellular matrix that resists compression. found in the vitreous humor of the eye and synovial fluid of joints, and in connective tissue like tendons, cartilage, etc, as well as skin. hyaluronan as a component in the synovial fluid lubricant in body joints, heparin as an anticoagulant, chondroitins, which can be found in connective tissues, cartilage, and tendons. VPP3021 Veterinary Biochemistry  GAGs ¢ hyaluronate, ¢ heparan sulfate/heparin, ¢ chondroitin sulfates, ¢ keratan sulfate ¢ dermatan sulfate VPP3021 Veterinary Biochemistry  Hyaluronate Hyaluronic acid or hyaluronate –is a copolymer of D-glucuronic acid and N-acetyl-D-glucosamine (Figure)- found in joint fluids, the inside of the eye and in the intracellular matrix of the human body. Composed of 250 to 25,000 b(1 4) linked disaccharide units that consist of glucuronic (COOH in 6 positions) and N-acetyl-D- glucosamine polymer linked by b(1 3) bond Act as shock absorber and lubricant In solution hyaluronate occupies a volume 1000 times that in its dry state VPP3021 Veterinary Biochemistry  Heparin naturally-occurring anticoagulant produced by basophils and mast cells widely used as an injectable anticoagulant (parenterally) parenterally because it is not absorbed from the gut, due to its high negative charge and large size has the highest negative charge density of any known biological molecule VPP3021 Veterinary Biochemistry  It works by activating antithrombin III, which blocks thrombin from clotting blood. Heparin binds to the enzyme inhibitor antithrombin III (AT) causing a conformational change that results in its activation The activated AT then inactivates thrombin and other proteases can be used in vivo (by injection), and also in vitro to prevent blood or plasma clotting in or on medical devices. Vacutainer brand test tubes containing heparin are usually colored green. Heparin and its derivatives (enoxaparin, dalteparin, tinzaparin) are effective at preventing deep-vein thromboses and pulmonary emboli VPP3021 Veterinary Biochemistry  Chondrotin sulfate Chondroitin sulfate- a major component of cartilage and other connective tissue containing two alternating monosaccharides: D-glucuronic acid (GlcA) and N-acetyl-D-galactosamine (GalNAc). Loss of chondroitin sulfate from the cartilage is a major cause of osteoarthritis. Chondroitin is an ingredient found commonly in dietary supplements used as an alternative medicine to treat osteoarthritis VPP3021 Veterinary Biochemistry  Keratan sulfate found especially in the cornea, cartilage, and bone. The amount of KS found in the cornea is 10 fold higher than it is in cartilage and 2-4 times higher than it is in other tissues Keratan sulfates are large, highly hydrated molecules which in joints can act as a cushion to absorb mechanical shock. VPP3021 Veterinary Biochemistry  Glycoproteins - Proteoglycans Proteoglycans are glycoproteins that are heavily glycosylated. They have a core protein with one or more covalently attached glycosaminoglycan (GAG) chain(s). The chains are long, linear carbohydrate polymers that are negatively charged under physiological conditions, due to the occurrence of sulfate and uronic acid groups VPP3021 Veterinary Biochemistry  Bristles consist of a core protein to which gags most often keratan sulfate and chondroitin sulfate are covalently linked Interaction between core protein and hyaluronate is stabilized by a link protein Oligosaccharides are glycosidically linked to the protein via amide N of specific Asn residues and therefore known as N-linked oligosaccharides Keratan sulfate and chondroitin sulfate chains are covalently bonded to side chain O atoms of specific Ser or Thr residues thus called O-linked oligosaccharides. VPP3021 Veterinary Biochemistry VPP3021 Veterinary Biochemistry  Please read the text book Bacterial cell walls Other glyco-conjugates such as glycoproteins and glycolipids Glycomics VPP3021 Veterinary Biochemistry  What we have discussed Introduction and general functions Monosacchrides - classification - sugar derivatives Polysaccharides - carbohydrate analysis - disaccharides - structural polysaccharides - storage polysaccharides - glycosaminoglycans Glycoproteins - proteoglycans - bacterial cell walls - glycoprotein structure and function - glycomics VPP3021 Veterinary Biochemistry