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  2. 2. Carbohydrates are polyhydroxy aldehydes orketones, or substances that yield suchcompounds on hydrolysis.Many, but not all, carbohydrates have theempirical formula (CH2O)n; some also containnitrogen, phosphorus, or sulfur.
  3. 3. There are three major size classes of carbohydrates 1. Monosaccharides simple sugars, consist of a single polyhydroxy aldehyde or ketone unit. The most abundant monosaccharide in nature is the six-carbon sugar D- glucose  Monosaccharides of more than four carbons tend to have cyclic structures.
  4. 4. 2. Oligosaccharides  Consist of short chains of monosaccharide units, or residues, joined by characteristic linkages called glycosidic bonds. The most abundant are the disaccharides, with two monosaccharide units. Typical is sucrose (cane sugar), which consists of the six-carbon sugars D-glucose and D-fructose.  In cells, most oligosaccharides consisting of three or more units do not occur as free entities but are joined to nonsugar molecules (lipids or proteins) in glycoconjugates.
  5. 5. 3. PolysaccharidesPolysaccharides are sugar polymers containingmore than 20 or so monosaccharide units, and somehave hundreds or thousands of units. Some polysaccharides, such as cellulose, are linearchains; others, such as glycogen, are branched. Both glycogen and cellulose consist of recurringunits of D-glucose, but they differ in the type ofglycosidic linkage and consequently have strikinglydifferent properties and biological roles.
  6. 6.  MONOSACCHARIDESAldoses (e.g., glucose) have Ketoses (e.g., fructose) havean aldehyde group at one a keto group, usually at C2.end. H O C CH2OH H C OH C O HO C H HO C H H C OH H C OH H C OH H C OH CH2OH CH2OH D-glucose D-fructose
  7. 7. D-Aldoses
  8. 8. D-ketoses EPIMERS
  9. 9. D vs L Designation CHO CHOD & L designations arebased on the H C OH HO C Hconfiguration about CH2OH CH2OHthe single asymmetric D-glyceraldehyde L-glyceraldehydeC in glyceraldehyde. CHO CHOThe lower H C OH HO C Hrepresentations areFischer Projections. CH2OH CH2OH D-glyceraldehyde L-glyceraldehyde
  10. 10. Sugar NomenclatureFor sugars with more O H O Hthan one chiral C Ccenter, D or L refers to H – C – OH HO – C – Hthe asymmetric C HO – C – H H – C – OHfarthest from the H – C – OH HO – C – Haldehyde or keto H – C – OH HO – C – Hgroup. CH2OH CH2OHMost naturally D-glucose L-glucoseoccurring sugars are Disomers.
  11. 11. Hemiacetal & hemiketal formation H HAn aldehyde canreact with an C O + R OH R O C OHalcohol to form R Ra hemiacetal. aldehyde alcohol hemiacetalA ketone can R Rreact with an C O + "R OH "R O C OHalcohol to form R Ra hemiketal. ketone alcohol hemiketal
  12. 12. Pentoses andhexoses can cyclizeas the ketone oraldehyde reactswith a distal OH.Glucose forms anintra-molecularhemiacetal, as theC1 aldehyde & C5OH react, to forma 6-memberpyranosering, named afterpyran. representations of the cyclic sugars are calledTheseHaworth projections.
  13. 13. 1 CH2OH 2C O HO C H 1 CH2OH 3 HOH2C 6 O H C OH 4 5 H HO 2 H C OH H 4 3 OH 5 OH H 6 CH2OH D-fructose (linear) -D-fructofuranoseFructose forms either a 6-member pyranose ring, by reaction of the C2 keto group with the OH on C6, or a 5-member furanose ring, by reaction of the C2 keto group with the OH on C5.
  14. 14. 6 CH 2OH 6 CH 2OH 5 O 5 O H H H OH H H 4 H 1 4 H 1 OH OH OH OH OH H 3 2 3 2 H OH H OH -D-glucose -D-glucoseCyclization of glucose produces a new asymmetric centerat C1. The 2 stereoisomers are called anomers, & .Haworth projections represent the cyclic sugars as havingessentially planar rings, with the OH at the anomeric C1:  (OH below the ring)  (OH above the ring).
  15. 15. Monosaccharides Are Reducing Agents Monosaccharides can be oxidized by relatively mild oxidizingagents such as ferric (Fe3+) or cupric (Cu2+) ion The carbonyl carbon is oxidized to a carboxyl group Glucose and other sugars capable of reducing ferric or cupricion are called reducing sugars. This property is the basis of Fehling’s reaction, a qualitativetest for the presence of reducing sugar. By measuring the amount of oxidizing agent reduced by asolution of a sugar, it is also possible to estimate the concentrationof that sugar For many years this test was used to detect and measureelevated glucose levels in blood and urine in the diagnosis ofdiabetes mellitus
  16. 16. Sugar derivatives COOH CHO CH2OH H C OH H C OH H C OH HO C H HO C H H C OH H C OH H C OH H C OH H C OH H C OH CH2OH CH2OH COOH D-ribitol D-gluconic acid D-glucuronic acid sugar alcohol - lacks an aldehyde or ketone; e.g., ribitol. sugar acid - the aldehyde at C1, or OH at C6, is oxidized to a carboxylic acid; e.g., gluconic acid, glucuronic acid.
  17. 17. CH2OH CH2OH H O H H O H H H OH H OH H OH OH OH O OH H NH2 H N C CH3 H -D-glucosamine -D-N-acetylglucosamineamino sugar - an amino group substitutes for a hydroxyl.An example is glucosamine.The amino group may be acetylated, as in N-acetylglucosamine.
  18. 18. O H H3C C NH O COO R HC OH H H R= HC OH H OH CH2OH OH H N-acetylneuraminate (sialic acid)N-acetylneuraminate (N-acetylneuraminic acid, alsocalled sialic acid) is often found as a terminal residueof oligosaccharide chains of glycoproteins.Sialic acid imparts negative charge toglycoproteins, because its carboxyl group tends todissociate a proton at physiological pH, as shown here.
  20. 20.  Disaccharides (such as maltose, lactose, and sucrose) consist oftwo monosaccharides joined covalently by an O-glycosidic bond, whichis formed when a hydroxyl group of one sugar reacts with theanomeric carbon of the other Glycosidic bonds are readily hydrolyzed by acid but resist cleavageby base,they can be hydrolyzed to yield their free monosaccharidecomponents by boiling with dilute acid.The oxidation of a sugar’s anomeric carbon by cupric or ferric ion(the reaction that defines a reducing sugar) occurs only with the linearform, which exists in equilibrium with the cyclic form When the anomeric carbon is involved in a glycosidic bond, thatsugar residue cannot take the linear form and therefore becomes anonreducing sugar  The end of a chain with a free anomeric carbon (one not involved in a glycosidic bond) is commonly called the reducing end.
  21. 21. Glc(α1→4)Glc.
  22. 22.  POLYSACCHARIDES (GLYCANS)  Most carbohydrates found in nature occur as polysaccharides, polymers of medium to high molecular weight. Differ from each other in: their monosaccharide units the length of their chains the types of bonds linking the units the degree of branching.  Homopolysaccharides contain only a single type of monomer  Heteropolysaccharides contain two or more different kinds
  23. 23.  Homopolysaccharides serve as: storage forms of monosaccharides that are used as fuels (starch and glycogen)  structural elements in plant cell walls and animal exoskeletons (cellulose and chitin,) Heteropolysaccharides provide extracellular supportfor organisms of all kingdoms.  the rigid layer of the bacterial cell envelope (peptidoglycan) is composed in part of a heteropolysaccharide built from two alternating monosaccharide units.  In animal tissues, the extracellular space is occupied by several types of heteropolysaccharides, which form a matrix that holds individual cells together and provides protection, shape, and support to cells, tissues, and organs.
  24. 24. Homopolysaccharides1. Some Homopolysaccharides Are Stored Forms of Fuel The most important storage polysaccharidesare:  starch in plant cells  glycogen in animal cells  Both polysaccharides occur intracellularly as large clusters or granules  Glycogen and starch ingested in the diet are hydrolyzed by α-amylases, enzymes in saliva and intestinal secretions that break (α1→4) glycosidic bonds between glucose units
  25. 25. StarchContains two types of glucose polymer, amylose and amylopectin  Amylose consists of long, unbranched chains of D-glucose residues connected by (α1→4) linkages, vary in molecular weight from a few thousand to more than a million  Amylopectin also has a high molecular weight (up to 100 million) but is highly branched. The glycosidic linkages joining successive glucose residues in amylopectin chains are (α1→4), the branch points (occurring every 24 to 30 residues) are (α1→6) linkages.
  26. 26. Glycogen  The main storage polysaccharide of animal cells  A polymer of (α1→4)-linked subunits of glucose, with (α1→6)-linked branches, but glycogen is more extensively branched on average, (every 8 to 12 residues) and more compact than starch.  especially abundant in the liver (7% of the wet weight)  also present in skeletal muscle
  27. 27. 2. Some Homopolysaccharides Serve Structural Roles Cellulose Cellulose, a fibrous, tough, water-insoluble substance, is found in thecell walls of plants Cellulose constitutes much of themass of wood, and cotton is almostpure cellulose cellulose molecule is alinear, unbranchedhomopolysaccharide,consisting of 10,000 to 15,000 D-glucose units. The glucose residues in cellulose arelinked by (β1→4) glycosidic bonds
  28. 28.  Most animals cannot use celluloseas a fuel source, because they lackan enzyme to hydrolyzethe (β1→4) linkages. Termites readily digest cellulose (andtherefore wood), but only because theirintestinal tract harbors a symbioticmicroorganism, Trichonympha, thatsecretes cellulase, which hydrolyzesthe (β1→4) linkages Wood-rot fungi and bacteria alsoproduce cellulase
  29. 29. Chitin a linear homopolysaccharide composed ofN-acetylglucosamine residues in β- linkage  the principal component of the hard exoskeletons of nearly a million species of arthropods—insects, lobsters, and crabs A spotted June beetle (Pellidnota punetatia), showing its surface armor  probably the second most abundant (exoskeleton) of chitin. polysaccharide, next to cellulose, in nature.
  30. 30. Heteropolysaccharides1. Bacterial Cell Walls Contain Structural Heteropolysaccharides The rigid component of bacterial cellwalls is a heteropolymer of alternating(β1→4)-linked N-acetylglucosamine andN-acetylmuramic acid residues The linear polymers lie side by side in thecell wall, crosslinked by short peptides The enzyme lysozyme kills bacteria byhydrolyzing the (β1→4)glycosidic bondbetween N-acetylglucosamine and N-acetylmuramic acid Penicillin and related antibiotics killbacteria by preventing synthesis of thecross-links, leaving the cell wall too weakto resist osmotic lysis
  31. 31. 2. Algal Cell Walls Contain Structural Heteropolysaccharides Certain marine red algae, including someof the seaweeds, have cell walls thatcontain agar, a mixture of sulfatedheteropolysaccharides made up of D-galactose and an L-galactose derivativeether-linked between C-3 and C-6 The two major components of agarare the unbranched polymer agarose(Mr ~120,000) and a branchedcomponent, agaropectin The remarkable gel-forming property of agarose makes it useful in the biochemistrylaboratory  Agarose gels are used as inert supports for the electrophoretic separation of nucleic acids, an essential part of the DNA sequencing process  Agar is also used to form a surface for the growth of bacterial colonies  Agar is also used for the capsules in which some vitamins and drugs are packaged
  32. 32. 3. Glycosaminoglycans Are Heteropolysaccharides of the Extracellular Matrix The extracellular space in the tissues ofmulticellular animals is filled with a gel-like material (ground substance), whichholds the cells together and provides aporous pathway for the diffusion ofnutrients and oxygen to individual cells The extracellular matrix is composed ofan interlocking meshwork ofheteropolysaccharides and fibrousproteins such ascollagen, elastin, fibronectin, andlaminin  These heteropolysaccharides, the glycosaminoglycans, are a family of linear polymers composed of repeating disaccharide units Glycosaminoglycans are attached toextracellular proteins to formproteoglycans
  33. 33. Hyaluronic Acid Serve as lubricants in the synovial fluid of joints and give the vitreous humor ofthe vertebrate eye its jellylike consistency An essential component of the extracellular matrix of cartilage andtendons, to which it contributes tensile strength and elasticity as a result of itsstrong interactions with other components of the matrix Hyaluronidase, an enzyme secreted by some pathogenic bacteria, canhydrolyze the glycosidic linkages of hyaluronate, rendering tissues moresusceptible to bacterial invasion  In many organisms, a similar enzyme in sperm hydrolyzes an outer glycosaminoglycan coat around the ovum, allowing sperm penetration
  34. 34. Chondroitin sulfate contributes to the tensile strength of cartilage, tendons, ligaments, and thewalls of the aortaDermatan sulfate (Greek derma, “skin”)  contributes to the pliability of skin and is also present in blood vessels and heart valves. Keratan sulfates  present in cornea, cartilage, bone, and a variety of horny structures formed of dead cells: horn, hair, hoofs, nails, and claws Heparin  a natural anticoagulant made in mast cells (a type of leukocyte) and released into the blood, where it inhibits blood coagulation by binding to the protein antithrombin