‹#› 1 SACCHARIDES © Department of Biochemistry 2010 – E.T. ‹#› 2 Saccharides occur widely in the nature, present in all types of cells – the major nutrient for heterotrophs – energy stores (glycogen, starch) – components of structural materials (glycosaminoglycans) – parts of important molecules (nucleic acids, nucleotides, glycoproteins, glycolipids) – signalling function (recognition of molecules and cells, antigenic determinants) ‹#› 3 Saccharides are polyhydroxyaldehydes and polyhydroxyketons Classification according to the number of monosaccharide units n: • monosaccharides • oligosaccharides: n = 2-10 • polysaccharides: n > 10 (hundreds to thousands monosaccharide units) ‹#› 4 Monosaccharides Aldoses Ketoses Trioses tetroses pentoses hexoses heptoses Aldehyde group Keto group ‹#› 5 Secondary alcoholic groups -CH-OH in monosaccharides are chiral centers -chiral centres are mostly carbon atoms that bind four different groups those atoms are often called "asymmetric" carbon atoms. D-glucose saccharides exists in form of stereoisomers Stereoisomerism and optical activity of saccharides ‹#› 6 Stereoisomers Compounds with the same structural formula but different space arrangement They differ in configuration ‹#› 7 C C C C C O O H H H H O H H C H 2 O H H H O O H C C C C C O O H H H H O H H C H 2 O H H H O O H D-glucose stereoisomer of D-glucose (one of many possible) The number of streoisomers of given compound – equals 2n n-number of chiral centers ‹#› 8 How many possible stereoisomers can be derived from glucose ? j0078711[1] ‹#› 9 Structures of some isomeric aldohexoses (the total number of possible isomers is 16) All of these monosaccharides have specific arrangement (configuration) on chiral centers C C C C C O H O H O H O H H O H H C H 2 O H H H C C C C C O H H O H O H H O H H C H 2 O H H H O C C C C C O H H O O H O H H O H H C H 2 O H H C C C C C O H O H H H O H H O H H C H 2 O H H O D-allose L-glucose D-glucose D-mannose H ‹#› 10 C C C C C O O H H H H O H H C H 2 O H H H O O H Assigning configurations D- and L- (from Latin dexter and laevus) Monosaccharides are classified as D- or L-sugars according to configuration at the configurational carbon atom (the chiral carbon with the highest numerical locant) configurational atom D - monosaccharide: OH- on configurational atom is to the right L- monosaccharide: OH- on configurational atom is to the left ‹#› 11 Common formulas of aldoses and ketoses ( C H O H ) n C O H C O H H C H 2 O H ( C H O H ) n C O H C H O H C H 2 O H C C H 2 O H O ( C H O H ) n C H H O C H 2 O H C C H 2 O H O ( C H O H ) n C O H H C H 2 O H D - aldose L - aldose D - ketose L - ketose ‹#› 12 The configuration on the other chiral centers cannot be deduced from assignement D-, L- (we must remember the configuration of the most common monosaccharides) j0078625[1] ‹#› 13 • Stereogenic centres in molecules of monosaccharides are the cause of their optical activity. • Solutions of mono- and oligosaccharides turn the plane of polarized light. • Optical activity is measured by using polarimeters and usually expressed as specific optical rotation. • Dextrorotatory substances are marked (+), laevorotatory (–). Optical activity of saccharides ‹#› 14 Each monosaccharide exists in form of two optical isomers (enantiomers) !!!!!! At all chiral carbons is opposite configuration C C C C C O O H H H O H H O H H C H 2 O H H H O C C C C C O H H H O O H H H O H H O C H 2 O H H D-glucose L-glucose ‹#› 15 MCAN02556_0000[1] Optical isomers (enantiomers) Specific pair of stereoisomers that differ in configuration at all chiral centers (relation os a subject and its mirror image) ‹#› 16 • have the same chemical properties •they differ by the direction in which they rotate the plane of polarized light (the absolute value of specific optical rotation is the same) •they differ in biological and pharmacological activity Enantiomers Most monosacharides in mammals have configuration D. Enzymes responsible for their metabolism are specific only for this configuration ‹#› 17 glyceraldehyde dihydroxyaceton * One chiral carbon The simplest monosaccharides (trioses) No chiral carbon ‹#› 18 Glyceraldehyde one chiral carbon Þ two enantiomers D-glyceraldehyde L-glyceraldehyde * * (-OH directs to the right) (-OH directs to the left) ‹#› 19 C C C C C H 2 O H O H H H O H H O H H O C C C C C H 2 O H O H H H O O H O H H H C C C C C H 2 O H O H O H H O H O H H H C C C C C H 2 O H O H H O H O H H H H O D - ribose D - arabinose D - xylose D - lyxose D- glyceraldehyde C C H 2 O H C O H O H H C C C C H 2 O H H O H H O H H O C C C C H 2 O H O H O H H O H H D- erythrose D- threose D-aldose tree – derived from D-glyeraldehyde ‹#› 20 C C C C C H H H C H H D-allose D- glyceraldehyde C C H 2 O H C O H O H H C C C C H 2 O H H O H H O H H O C C C C H 2 O H O H O H H O H H D- erythrose D- threose O O H O H O H O H H 2 O H C C C C C O H H O H O H H O H H C H 2 O H H H O C C C C C O H H O O H O H H O H H C H 2 O H H C C C C C O H O H H H O H H O H H C H 2 O H H O D-althrose D-glucose D-mannose C C C C C H 2 O H O H H H O H H O H H O C C C C C H 2 O H O H H H O O H O H H H C C C C C H 2 O H O H O H H O H O H H H C C C C C H 2 O H O H H O H O H H H H O D- ribose D- arabinose D- xylose D- lyxose C C C C C O H H O O H H H O O H H C H 2 O H H H C C C C C O H H O H H H O O H H C H 2 O H O H H C C C C C O H H H H H O O H H C H 2 O H O H H O C C C C C H H O H H H O O H H C H 2 O H H H O O D-gulose D-idose D-galactose D-talose D-aldose tree ‹#› 21 Cyclic forms of monosaccharides Hemiacetals are formed by reaction of carbonyl group with alcohol group ??? Molecules of monosaccharides spontaneously form cyclic hemiacetal forms in solutions. http://www.stolaf.edu/people/giannini/flashanimat/carbohydrates/glucose.swf ‹#› 22 Cyklization: C1 becomes chiral atom =O ® OH........hemiacetal hydroxyl group Þ two new stereoisomers are formed – anomers (a a b ) In cyclic forms of hemiacetals: -OH and -C=O originate from the same molecule ‹#› 23 * * * * C C C O H H H H O C C O H H C H 2 O H O H H O H * * * * * C C C O H H H H O C C O H H C H 2 O H O H H O H * a- anomer – the configuration on the anomeric carbon is the same as the configuration on the configurational carbon atom (in D-forms is OH on the C1 on the right side) b- anomer –the configuration on the anomeric carbon is opposite as the configuration on the configurational carbon atom (in D-forms is OH on the C1 on the left side) a b ‹#› 24 Rings: six-membered pyranoses five-membered furanoses Names of the cyclic forms express the type of the cyclic form and the type of the anomer ‹#› 25 * * * * C C C O H H H H O C C O H H C H 2 O H O H H O H * O O H O H O H O H O H 1 6 Projections of cyclic forms: α-D-glucopyranose Fischer formula Haworth projection ‹#› 26 Rules for drawing Haworth projections (simplyfied) •Heterocycle is expressed by the pentagon or hexagon lying perpendicular to the plane of the paper •Anomeric carbon is on the right-hand end • Oxygen atom is behind •The atoms are numbered clockwise around the ring •Groups that appear to the right in the modified Fischer formula appear below the plane of the ring, those on the left appear above • The group is directed abwards in D-sugars O 1 2 3 CH2OH CH2OH ‹#› 27 H O O O H H H O H O H C H H O H C H 2 O H C C C C C O H H H H O H H C H 2 O H H O O O H H b -D-glucofuranose C C C C C O H H H O H H H C H 2 O H O H H O H O O O H O H O H C H 2 O H b - D-glucopyranose Further possible cyclic forms of glucose ‹#› 28 Cyclic forms of fructose b-D-fructopyranose C H 2 O H C C C H 2 O H C C H O H H O H H H O O O H O H O H H O H C H 2 O H H C H 2 O H 1 2 b -D-fructofuranose D-fructose O C H 2 O H O H O H O H O H 1 ‹#› 29 Epimers – diastereomers differing in configuration at just one chiral carbon atom Enantiomers (optical antipodes): D- and L-form of the same monosaccharide, they differ in configuration at all chiral centres Don't confuse: Diastereomers – stereoisomers that differ in configuration at least at one chiral carbon and are equal in configuration at least at one chiral atom Anomers - cyclic forms of the given monosaccharide that differ in configuration only on the anomeric carbon atom ‹#› 30 Properties of monosaccharides Soluble in water (polar) non soluble in organic solvents Non-electrolytes do not dissociate in aqueous solution More or less sweet to the taste ‹#› 31 Oxidation of monosaccharides C C C C C C H 2 O H O H Aldonic acids Uronic acids Aldaric acids ‹#› 32 C C C C C C H 2 O H O H O H H H H O O H H H O H C C C C C H 2 O H C H 2 O H H H O O H H H O O H C C C C C H 2 O H C H 2 O H O H H H H O O H H H O H C C C C C H 2 O H C H 2 O H H H O H H O O H H H O H D-glucose D-fructose D-glucitol D-mannitol Reduction of carbonyl group Sugar alcohols (alditols) Reduction of fructose provides two alcohols ‹#› 33 1/2 O2 D-gluconic acid With acyclic form proceeds as oxygenation ( oxygen is bonded) Formation of gluconic acid pKa=3,86 ‹#› 34 Formation of cyclic form of gluconic acid – lactone – it proceeds in aqueous solution O O H O H O H C H 2 O H O D-glucono-1,5-lacton -H2O Lactones are „intramolecular (cyclic) esters“ They are formed in reaction between carboxylic and alkohol group in the same molecule, water is released ‹#› 35 Gluconolactone is formed also by oxidation of cyclic form of glucose (proceeds as dehydrogenation) – As in organism mainly cyclic form of glucose is present, this type of glucose oxidation is prevailing. Reaction is catalyzed by glucose-6P-dehydrogenase. D-glucopyranose D-glucono-1,5-lacton -2H O O H O H O H H O H H C H 2 O H mild oxidation H ‹#› 36 Uronic acids Formed by double oxidation of the last carbon In organism it is formed by oxidation of cyclic form of glucose (hemiacetal group is retained) C C C C C C O O H O O H H H H O O H H O H H H D-glucuronic acid O O H O H O H O H C O O H ‹#› 37 C C C C C C H 2 O H O H O H H H H O O H H H O H C C C C C H 2 O H C H 2 O H H H O O H H H O O H C C C C C H 2 O H C H 2 O H O H H H H O O H H H O H C C C C C H 2 O H C H 2 O H H H O H H O O H H H O H D-glucose D-fructose D-glucitol D-mannitol Reduction of carbonyl group Sugar alcohols (alditols) Reduction of fructose provides two alcohols ‹#› 38 Important monosaccharides ‹#› 39 • most abundant sugar in the nature „grape sugar“ contained in starch, glycogen and cellulose • concentration in blood ( 3,3-5,5 mmol/l) is strictly regulated D – Glucose O O H O H O H O H C H 2 O H foto-401-589 ‹#› 40 • epimer of glucose – opposit configuration on C-4 • component of lactose (disaccharide), glycoproteins, glycolipids, proteoglycans D - Galactose O O H O H O H O H C H 2 O H ‹#› 41 • „fruit sugar“ • most wideapread ketose • free in honey, fruits • component of sucrose D – fructose O H O H O H H O H C H 2 O H H C H 2 O H Pak_Pure_Honey.jpg honey image by hilliethekid ‹#› 42 • pentoses • building unit of nucleic acids D-ribose a D-2-deoxyribose O O H O H O H H O O O H H O H H O ‹#› 43 Derivatives of monosaccharides Esters · with phosphoric acid H glucose-1-phosphate O O H O H O H H H O H H C H 2 O H P O O O H O O H H H O H O H H H O H H C H 2 O P O O H H O glucose-6-phosphate Intermediates in metabolism of glucose H ‹#› 44 O O H O H H 2 C O P O H O O H C H 2 O P O O H O H fructose-1,6-bisphosphate OH Intermediate in metabolism of glucose ‹#› 45 Aminosugars O O H H H N H 2 O H H H O H H C H 2 O H D-glucosamine (2-amino-2-deoxy-D-glucose) C H O O H H H N H O H H H O H H C O C H 3 2 O H N-acetylglucosamine Component of proteoglycans and glycoproteins ‹#› 46 O O OH O H C H O H C H 2 O H L-ascorbic acid Derivative of L-gulonic acid Weak diprotic acid ‹#› 47 Sialic acids N H C O C H 3 O H C H O H C O O H O H C H O H C H 2 O H O H O H C H O H C O O H O H C H O H C H 2 O H O H N H 2 Neuraminic acid N-acetylneuraminic acid Component of gangliosides, glycoproteins, proteoglycans ‹#› 48 Glycosides – Derivatives of cyclic forms of monosaccharides arising by reaction on hemiacetal hydroxyl group of a saccharide : – – reaction with alcoholic or phenolic group of another compound O-glycosides with NH- group of another compound N-glycosides ‹#› 49 Methyl-b-D-glucopyranoside Formation of glycosidic bond O O H O H O H O H C H 2 O H + C H 3 O H O O C H 3 O H O H O H C H 2 O H Glycosidic bond -H 2 O ‹#› 50 N-glycosidid bond N-glycosidic bond nucleosides ‹#› 51 Disaccharides • The most important oligosaccharides • Two monosaccharides joined by glycosidic bond O-glycosides two types of these sugars – reducing and nonreducing disaccharides. Reducing disaccharides - formed by a reaction between the anomeric hydroxyl of one monosaccharide and a alcoholic hydroxyl group of another Nonreducing disaccharides - both anomeric hydroxyl groups are linked in the glycosidic bond ‹#› 52 a) Reducing disaccharides Maltose • „malt sugar“ • contained in malt, formed by enzymic hydrolysis of starch in the intestine • 2 molecules of glucose, a - 1,4 glycosidic bond a - maltose 4-O-a-D-glucopyranosyl- a-D-glucopyranose ‹#› 53 Lactose • „milk sugar“ • galactose and glucose, b-1,4 glycosidic bond • milk : cow 4-6% human 6% a - lactose 4-O-b-D-galactopyranosyl-a-D-glucopyranose milk ‹#› 54 b) Nonreducing disaccharides Sucrose Beet/cane sugar name: “glycosyl-glycoside” b-D-fruktofuranosyl-a-D-glucopyranoside 2 glucose a fructose b-2,1 glycosidic bond 1 ‹#› 55 Polysaccharides • several hunreds to thousands monosaccharide units • glycosidic bond : a - glycosidic bond vazba b - glycosidic bond mostly 1® 4 a 1 ® 6 • chains are linear or branched • non soluble in water, some form colloidal solutions • not sweet ‹#› 56 Clasification of polysaccharides Homopolysaccharides Contain one type of monosaccharide (starch, glycogen, cellulose, inulin) Heteropolysaccharides Contain two or more monosaccharides or their derivatives (glycosaminoglycans, hyaluronic acid, glucofructans) ‹#› 57 Biochemical significance of polysaccharides •Store of energy • starch (plants), glycogen (animals) •Structural function • cellulose (plants), proteoglycans of connective tissue (animals) •Component of glycoproteins (affects biological function of proteins) ‹#› 58 Starch •lat. amylum, •Storage polysaccharide of plants •Main source of energy for human •In hot water forms colloidal solution •Monosaccharide subunit is D-glucose, •two types of chains Amylose •20-30 % •a-1,4 bonds •linear (helix) •soluble in water Amylopectin •70-80 % •a-1,4 + a-1,6 bonds •branched •non soluble in water ‹#› 59 Structure of amylose Structure of amylopectin ‹#› 60 Starch is the main source of saccharides in food • it is digested by α-amylase in mouth and intestine •α-amylase hydrolyses α-(1®4) glycosidic bonds • the product of digestion is maltose, isomaltose, they are further digested by specific enzymes • the final product of cleavage is glucose Distinguish: : amylase x amylose !!!! ŠKROB (AMYLUM) ‹#› 61 • storage substance in animals (liver, muscle) • „animal starch“ • formed from sugars taken in food • composed of glucose units • structurally similar to amylopectin branched chain: bonds a-1,4 and a-1,6 ® branching Glycogen Glycogen stores in man Liver 4-6 % of liver mass Muscle 1-2 % of muscle mass ‹#› 62 Glycogen branching α-1,4 α-1,6 ‹#› 63 Cellulose •Most abundant organic compound in plants •Composed of D-glucose, bonds b-1,4 •Fibrous macromolecules joined by hydrogen bonds •Not soluble in water •Not digestible for humans and most animals, is the main component of dietary fibre ‹#› 64 Intra- and inter- molecular hydrogen bonds in cellulose Formation of fibers and bundles. Cotton, wood, hemp, linen, straw, and corncobs are mainly cellulose ‹#› 65 Cellulose cleavage • bonds b-(1®4) can not be cleaved by α-amylase Cellulose is not digestible by human Ruminants have microorganisms in their digestion tract that are producing b-glucosidases – they can utilize cellulose as a source of glucose MCj02994910000[1] ‹#› 66 Dextrans •Polysaccharides containing D-glucose, bonds α-1,6 •Special type of branching (positions 3 and 4) •Formed from saccharose by the action of bacteria •Molecular mass 10 000 – 1 000 000 •Used as artificial substitute of blood plasma (at bleeding or therapy of burns) •Highly branched dextrans prepared artificially are used as molecular sieves for gel chromatography ‹#› 67 Structure of dextran 1,3-branching ‹#› 68 Dextran and caries •bacterias of oral cavity (e.g.. Streptococcus mutans) cleave sucrose to glucose a fructose •bacterial enzyme dextran transglucosylase catalyzes synthesis of dextran from glucose •dextran is not soluble in water and resistant against salivary amylase, it builds up coatings on unclean teeth– it is a mixture of dextrans and bacterias •bacterias metabolize fructose to lactic acid (pKA = 3,86), that has corrosive effect on enamel ‹#› 69 Heteropolysacharides Glycosaminoglycans (mucopolysacharides) • non-branched heteropolysacharides •Components of proteoglycans and peptidoglycans • formed by repeating disaccharide units: [ glycosamin – uronic acid]n Glukosamin, galaktosamin (often acetylated) Glucuronic, galacturonic, iduronic Specific –OH groups may be sulfated ‹#› 70 Major types of glycosaminoglycans (GAG) Heteroglycan •hyaluronic acid •chondroitin-4-sulfate •chondroitin-6-sulfate •keratansulfate •heparin •dermatansulfate Compositon •Glc-NAc, Glc-UA •Gal-NAc-4-sulfate, Glc-UA •Gal-NAc-6-sulfate, Glc-UA, •Gal-NAc, sulfate •Glc-NAc, Glc/Ido-UA, sulfate •Gal-NAc, Glc/Ido-UA, sulfate ‹#› 71 Heparin •Prevents blood clotting in vivo + in vitro •Forms the complex with antitrombin •It is released from basophillic granules of mast cells •Therapeutically used to prevent and treat tromboses, after IM, surgical operations etc. •Preparation of uncoaguable blood ‹#› 72 Glycosaminoglycans are often components of proteoglycans Proteoglycans • complexes of glycosaminoglycans and specific proteins • content of heteroglycans up to 95 %, chains of 10-100 saccharide units • most often O-glykosidic bond between a protein and glycan, end- sequence Gal-Gal-Xyl • present mainly in extracellular matrix of animals protein jádra N-konec řetězce GAG Chains of GAG Core protein It resembles a bottle-brush ‹#› 73 Hyaluronic acid Link protein Core protein Heteroglycans Core proteins are associated with hyaluronate by link proteins Complexes of proteoglycans The length of hyaluronate strand is up to 4000 nm ‹#› 74 Main components of extracellular matrix Fibronectine Cell cytoskeleton Elastic fibres proteoglycans Hyaluronic acid Collagen receptor Meisenberg, Simmons:Principles of Medical Biochemistry ‹#› 75 Nucleosides a nucleotides ‹#› 76 Numbering 1,3-diazine Pyrimidine a derivatives ‹#› 77 Pyrimidine bases N N N H 2 H O N N O H H O N N O H H O C H 3 cytosine uracil thymine 2-hydroxy-4-aminopyrimidine 2,4-dihydroxypyrimidine 2,4-dihydroxy-5-methylpyrimidine ‹#› 78 Tautomerism of pyrimidine bases N N O H H O N N O O H H lactime form (weakly acidic) lactam form (more stabile) ‹#› 79 Purine has special numbering Purine and derivatives ‹#› 80 Purine bases N N N H 2 N N H N N O H N N H H 2 N adenine guanine 6-aminopurine 2-amino-6-hydroxypurine ‹#› 81 N N O H N N H H O N N O H N N H hypoxantine xantine They are formed by metabolism of purine bases 6-hydroxypurine 2,6-dihydroxypurine ‹#› 82 N N O H N N H O H H O Uric acid (acidum uricum) At mammals: final product of purine bases metabolism Uricotel organisms (most of reptiles and birds): it is formed from amino acids. 2,6,8-trihydroxypurine ‹#› 83 N N O H N N H O H H O Tautomeris forms of uric acid lactime lactame D H ‹#› 84 Lactime form is diprotic acid uric acid hydrogenurate urate pKA1 = 5,4 pKA2 = 10,3 2,6,8-trihydroxypurine ‹#› 85 Uric acid is very bad soluble in water or in acidic medium It dissolves in alkaline medium and forms salts ( urates and hydrogenurates) N N O H N N H O N a H O Sodium hydrogenurate ‹#› 86 Consequences of bad solubility in human body Under patological conditions •Formation of renal stones • deposition in joints and tissues (gout) ‹#› 87 DnaW ‹#› 88 base + ribose base + 2-deoxyribose b-N-glycosidic bond Nucleosides ‹#› 89 General structure of nucleoside O base pentosa b - N -glycosidic bond ‹#› 90 Names of nucleosides •Trivial names •Derived from names of bases •ending -idine (pyrimidine nucleosides) •přípona -osine (purine nucleosides) ‹#› 91 Pyrimidine nucleosides O O H O H H O C H 2 O O N H N O O H O H H O C H 2 O N N N H 2 O O H H O C H 2 O O N H N C H 3 uridine cytidine thymidine ‹#› 92 Purine nucleosides O O H O H H O C H 2 N N N N N H 2 O O H O H H N N N N H 2 N H O C H 2 O guanosine adenosine ‹#› 93 O O H O H H O C H 2 N N N N O O H O H H N N N N H O C H 2 O O H H O H inosine xanthosine Purine nucleosides ‹#› 94 Nucleotides Nucleoside + phosphoric acid bound by ester bond to: ribose (C2´,C3´, C5´) deoxyribose (C3´,C5´) ‹#› 95 General structure of nucleotide O base pentosa phosphate 1' 5' b-N-glycosidic bond Ester bond ‹#› 96 Names of nucleotides •nucleoside + 5‘-mono(di, tri) + phosphate •abbreviations AMP, ADP, ATP ………... ‹#› 97 Significance of nucleotides •Building blocks of nucleic acids •Macroergic compounds (ATP, CTP, UTP) •Second messengers (cAMP, cGMP) •Cofactors of enzymes •syntetic analogs - therapeutics • ‹#› 98 Adenosin-5´- monophosphate (AMP) O O H O H C H 2 O P O O O N N N N N H 2 ‹#› 99 Adenosine-5´- triphopshate (ATP) P O O O P O O O O O H O H C H 2 O P O O O N N N N N H 2 ‹#› 100 cAMP – secondary messenger ‹#› 101 NAD+ is dinucleotide ‹#› 102 Flavine adenine dinucleotide (FAD) isoalloxazine ribitol