CHAPTER 07B

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Section 7.1: Monosaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Important Monosaccharides Glucose ( D -Glucose)- originally called dextrose, it’s found in large quantities throughout the natural world The primary fuel for living cells Preferred energy source for brain cells and cells without mitochondria (erythrocytes) Figure 7.21 a - D -glucopyranose

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Section 7.1: Monosaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Fructose ( D -Fructose) is often referred to as fruit sugar, because of its high content in fruit On a per gram basis, it is twice as sweet as sucrose, therefore it is often used as a sweetening agent in processed food Sperm use sugar as an energy source Figure 7.22 b -D-fructofuranose

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Section 7.1: Monosaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Galactose is necessary to synthesize a variety of important biomolecules Important biomolecules include: lactose, glycolipids, phospholipids, proetoglycan, and glycoproteins Epimerase can interconvert glucose and galactose Galactosemia is a genetic disorder resulting from a missing enzyme in galactose metabolism Figure 7.23 a -D-galactopyranose

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Section 7.1: Monosaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Monosaccharide Derivatives Uronic Acids- a - D - glucuronate (7.24a) and its epimer b - L - iduronate (7.24b) are important in animals D - Glucuronic acid is used in the liver to improve water solubility to remove waste molecules Figure 7.24 Uronic Acids

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Section 7.1: Monosaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Monosaccharide Derivatives Continued Amino Sugars- in amino sugars, a hydroxyl group (usually on carbon 2) is replaced with an amine group D -Glucosamine and D - galactosamine are the most common and often attached to proteins or lipids Figure 7.25 Amino Sugars

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Section 7.1: Monosaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Monosaccharide Derivatives Continued Deoxy Sugars- Monosaccharides that have an –OH replaced by an –H or –CH 3 2-deoxy- D -ribose (7.25b) is the pentose sugar of DNA and fucose (7.25a) is part of ABO blood group determinants Figure 7.26 Deoxy Sugars

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Section 7.2: Disaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Disaccharides Two monosaccharides linked by a glycosidic bond Linkages are named a - or b -conformation and by which carbons are connected (e.g., a (1,4) or b (1,4)) Figure 7.27 Glycosidic Bonds

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Section 7.2: Disaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Disaccharides Continued Lactose ( milk sugar ) is the disaccharide found in milk One molecule of galactose linked to one molecule of glucose ( b (1,4) linkage) It is common to have a lactase deficiency Lactose is a reducing sugar Figure 7.28 a - and b -lactose

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Section 7.2: Disaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Disaccharides Continued Maltose ( malt sugar ) is an intermediate product of starch hydrolysis a (1,4) linkage between two molecules of glucose Does not exist freely in nature Figure 7.29 a - and b -Maltose

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Section 7.2: Disaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Disaccharides Continued Cellobiose is a degradation product of cellulose Cellobiose is composed of two molecules of glucose linked with a b (1,4) glycosidic bond Does not exist freely in nature Figure 7.30 b -Cellobiose

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Section 7.2: Disaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Disaccharides Continued Sucrose is common table sugar (cane or beet sugar) produced in the leaves and stems of plants One molecule of glucose linked to one molecule of fructose, linked by an a , b (1,2) glycosidic bond Glycosidic bond occurs between both anomeric carbons Sucrose is a nonreducing sugar Figure 7.31 Sucrose

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Polysaccharides ( glycans ) are composed of large numbers of monosaccharides connected by glycosidic linkages Smaller glycans made of 10 to 15 monomers called oligosaccharides, most often attached to polypeptides as glycoproteins Two broad classes N- and O-linked oligosaccharides

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press N-linked oligosaccharides are attached to polypeptides by an N-glycosidic bond with the side chain amide group from the amino acid asparagine Figure 7.32 Oligosaccharides Linked to Polypeptides

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Three major types of asparagine-linked oligosaccharides: high mannose , hybrid , and complex O-Glycosidic linkages attach glycans to the side chain hydroxyl of serine or threonine residues, or the hydroxyl oxygens of membrane lipids Figure 7.32 Oligosaccharides Linked to Polypeptides

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Larger glycans may be hundreds or thousands of subunits Polysaccharides can be linear or branched Polysaccharides have been divided into two classes: homoglycans and heteroglycans Homoglycans Have one type of monosaccharide and found in starch, glycogen, cellulose, and chitin Starch and glycogen are energy storage molecules while chitin and cellulose are structural

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Homoglycans Chitin is part of the cell wall of fungi and arthropod exoskeleton Cellulose is the primary component of plant cell walls No fixed molecular weight, because the size is a reflection of the metabolic state of the cell producing them

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Starch- the energy reservoir of plant cells and a significant source of carbohydrate in the human diet Two polysaccharides occur together in starch: amylose and amylopectin Amylose is composed of long, unbranched chains of D -glucose with a (1,4) linkages between them Figure 7.33 Amylose

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Amylose typically contains thousands of glucose monomers and a molecular weight from 150,000-600,000 D The other form is amylopectin , which is a branched polymer containing both a (1,6) and a (1,4) linkages Branch points occur every 20 to 25 residues Figure 7.33 Amylose

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Glycogen is the carbohydrate storage molecule in vertebrates found in greatest abundance in the liver and muscle cells Up to 8–10% of the wet weight of liver cells and 2–3% in muscle cells Similar in structure to amylopectin, with more branch points More compact and easily mobilized than other polysaccharides

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 7.34 (a) Amylopectin and (b) Glycogen

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Cellulose is a polymer of D -glucopyranosides linked by b (1,4) glycosidic bonds It is the most important structural polysaccharide of plants (most abundant organic substance on earth) Figure 7.35 Cellulose

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Pairs of unbranched cellulose molecules (12,000 glucose units each) are held together by hydrogen bonding to form sheetlike strips, or microfibrils Each microfibril bundle may contain 40 of these pairs Important for dietary fiber, wood, paper, and textiles Figure 7.36 Cellulose Microfibrils

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Heteroglycans High molecular weight carbohydrate polymers that contain more than one type of monosaccharide Major types: N- and O-linked glycosaminoglycans (glycans), glycosaminoglycans , glycan components of glycolipids , and GPI ( glycosylphosphatidylinositol ) anchors GPI anchors and glycolipids will be discussed in chapter 11

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Heteroglycans Continued N- and O- Glycans - many proteins have N- and O-linked oligosacchaarides N-linked ( N- glycans ) are linked via a b - glycosidic bond O-linked (O- glycans ) have a disaccharide core of galactosyl - b -(1,3)-N- acetylgalactosamine linked via an a - glycosidic bond to the hydroxyl of serine or threonine residues

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Heteroglycans Continued Glycosaminoglycans (GAGs) are linear polymers with disaccharide repeating units Five classes: hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparin and heparin sulfate, and keratin sulfate Varying uses based on repeating unit

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Section 7.3: Polysaccharides From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press

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Section 7.4: Glycoconjugates From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Glycoconjugates result from carbohydrates being linked to proteins and lipids Proteoglycans Distinguished from other glycoproteins by their high carbohydrate content (about 95%) Occur on cell surfaces or are secreted to the extracellular matrix Figure 7.37 Proteoglycan Aggregate

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Section 7.4: Glycoconjugates From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Proteoglycans Continued All proteoglycans contain GAG chains that are linked to core proteins by N- and O-glycosidic bonds Aggrecan is an example of a type of proteoglycan that is found in abundance in cartilage It is a core protein linked to over 100 chondroitin sulfate and 40 keratin sulfate chains Up to 100 aggrecan are in turn attached to hyaluronic acid to form a proteoglycan aggregate

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Section 7.4: Glycoconjugates From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Proteoglycans Continued Have roles in organizing extracellular matrix and are involved in signal transduction Metabolism of proteoglycans involved in many genetic disorders, including Hurler’s syndrome Figure 7.37 Proteoglycan Aggregate

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Section 7.4: Glycoconjugates From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Glycoproteins Commonly defined as proteins that are covalently linked to carbohydrates through N- and O-linkages Several addition reactions in the lumen of the endoplasmic reticulum and Golgi complex are responsible for final N-linked oligosaccharide structure O- glycan synthesis occurs later, probably initiating in the Golgi complex Carbohydrate could be 1%–85% of total weight

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Section 7.4: Glycoconjugates From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Glycoprotein Functions occur in cells as soluble and membrane-bound forms, and are nearly ubiquitous in living organisms Vertebrate animals are particularly rich in glycoproteins Figure 7.37 Antifreeze Glycoprotein

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Section 7.4: Glycoconjugates From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Functions of glycoproteins include: enzymes, blood clotting, hormone, receptor proteins, transport proteins, and cell adhesion

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Section 7.4: Glycoconjugates From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 7.39 The Glycocalyx

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Section 7.5: The Sugar Code From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Living organisms require large coding capacities for information transfer Profound complexity of functioning systems To succeed as a coding mechanism, a class of molecules must have a large capacity for variation Glycosylation is the most important posttranslational modification in terms of coding capacity More possibilities with hexasaccharides than hexapeptides

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Section 7.5: The Sugar Code From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press In addition to their immense combinatorial possibilities they are also relatively inflexible, which makes them perfect for precise ligand binding Lectins Lectins , or carbohydrate binding proteins, are involved in translating the sugar code Bind specifically to carbohydrates via hydrogen bonding, van der Waals forces, and hydrophobic interactions

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Section 7.5: The Sugar Code From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Figure 7.40 Role of Oligosaccharides in Biological Recognition Lectins Continued Biological processes include: binding to microorganisms, binding to toxins, and involved in leukocyte rolling

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Section 7.5: The Sugar Code From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press The Glycome Total set of sugars and glycans in a cell or organism is the glycome Constantly in flux depending on the cell’s response to environment There is no template for glycan biosynthesis; it is done in a stepwise process Glycoforms can result based upon slight variations in glycan composition of each glycoprotein

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Biochemistry in Perspective From McKee and McKee, Biochemistry , 4th Edition, © 2009 Oxford University Press Sweet Medicine Carbohydrates involvement in health 200 genes encode for glycan processing enzymes and nearly 50% of proteins are linked to a carbohydrate group There are 30 rare genetic disorders classified as congenital disorders of glycosylation Numerous carbohydrate-based drugs: Enzyme inhibitors Enzyme replacement Vaccines Redesigned d rugs

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