figure 7.16 acetals and ketals can be formed from hemiacetals and hemiketals, respectively

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Figure 7.16 Acetals and ketals can be formed from hemiacetals and hemiketals, respectively. . Sugar acetals are called glycosides . - glycosides are stable compounds - they do not mutarotate. - PowerPoint PPT Presentation

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Figure 7.16 Acetals and ketals can be formed from hemiacetals and hemiketals, respectively.

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Sugar acetals are called glycosides.- glycosides are stable compounds - they do not mutarotate22Figure 7.18 The structures of several important disaccharides. Note that the notation -HOH means that the configuration can be either or . If the -OH group is above the ring, the configuration is termed . The configuration is if the -OH group is below the ring as shown. Also note that sucrose has no free anomeric carbon atoms.

33Fig. 7-18a, p.216a nonreducing sugar44ACTIVE FIGURE 7.18 The structures of several important disaccharides. Note that the notation XHOH means that the configuration can be either or . If the XOH group is above the ring, the configuration is termed . The configuration is if the XOH group is below the ring. Also note that sucrose has no free anomeric carbon atoms. Test yourself on the concepts in this figure at http://chemistry.brookscole.com/ggb3

Fehlings reaction for aldehyde(can also detect ketones after tautamerization)Trehalose A Natural Protectant for Bugs

Insects use an open circulatory system to circulate hemolymph (insect blood). The blood sugar is trehalose, an unusual, nonreducing disaccharide. Trehalose may act as a natural cryoprotectant, protecting the insect from damage due to freezing temperatures.6

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88 Lactose tolerance is widespread among people who come from areas that have a long history of dairy farming - including Northern Europe, the Middle East and India - or who rely extensively on milk in their diets, such as the Fulani in West Africa or the Masai in East Africa. But adults from other areas - such as East Asia and much of Africa - remain lactose intolerant, and find it difficult to digest milk.99A Variety of Higher Oligosaccharides Occur in Nature

Oligosaccharides occur widely as components of antibiotics (derived from various sources). Figure 7.19 Erythromycin is an antibiotic produced by a strain of Streptomyces erythreus.10A Variety of Higher Oligosaccharides Occur in Nature

Figure 7.19 Streptomycin is an oligosaccharide produced by Stretomyces griseus.Oligosaccharides occur widely as components of antibiotics (derived from various sources).

117.4 What is the Structure and Chemistry of Polysaccharides?Functions: storage, structure, recognition Nomenclature for polysaccharides is based on their composition and structure Homopolysaccharide a polysaccharide that contains only one kind of monosaccharideHeteropolysaccharide a polysaccharide made of several monosaccharidesStarch and glycogen are storage molecules Chitin and cellulose are structural molecules Cell surface polysaccharides are recognition molecules 12StarchA plant storage polysaccharide

Two forms: amylose and amylopectin Most starch is 10-30% amylose and 70-90% amylopectin Branches in amylopectin every 12-30 residues Amylose has alpha(1,4) links, one reducing end The branches in amylopectin are (16).13Amylose and Amylopectin are energy storage molecules in plants

Figure 7.20 Amylose and amylopectin are two forms of starch. Amylopectin is highly branched, with branches occurring every 12 to 30 residues.14The Structure of AmyloseAmylose is poorly soluble in water, but forms micellar suspensions In these suspensions, amylose is helicalIodine fits into the helices to produce a blue color15The Structure of Amylose

Figure 7.21 Suspensions of amylose in water adopt a helical conformation. Iodine (I2) can fit into the middle of the amylose helix to give a blue color that is characteristic and diagnostic for starch.16The Phosphorylase Reaction Releases Glucose Units for Metabolic Energy

Figure 7.22 The starch phosphorylase reactions cleaves glucose residues from amylose, producing -D-glucose-1-phosphate, an energy source for the organism. 17GlycogenThe glucose storage device in animals

Glycogen constitutes up to 10% of liver mass and 1-2% of muscle mass Glycogen is stored energy for the organism Only difference from amylopectin: the frequency of branching Alpha(1,6) branches every 8-12 residues Like amylopectin, glycogen gives a red-violet color with iodine18DextransA small but significant difference from starch and glycogen

If you change the main linkages between glucose from alpha(1,4) to alpha(1,6), you get a new family of polysaccharides - dextrans Branches can be (1,2), (1,3), or (1,4) 19Roles for DextransDextrans formed by bacteria are components of dental plaqueDextrans in plaque presumably provide protection for oral bacteria Cross-linked dextrans are used as "Sephadex" gels in column chromatography These gels, used to separate biomolecules on the basis of size, are up to 98% water!20Structural PolysaccharidesThe composition of structural polysaccharides is similar to storage polysaccharidesBut small structural differences greatly influence propertiesStarch and glycogen linkages consist primarily of (14) linkages. Cellulose consists of (14) linkages

21Cellulose Provides Physical Structure and Strength to PlantsCellulose is a structural polysaccharideIt is the most abundant natural polymer in the worldIt is found in the cell walls of nearly all plantsThe wood and bark of trees are insoluble, highly organized structures formed from cellulose and ligninCotton is almost pure celluloseCotton acetates, made from the action of acetic anhydride on cellulose, are used in dresses, lingerie, and other clothing22The Structural Difference Between Amylose and Cellulose

Figure 7.23 (a) Amylose prefers a helical conformation (due to its bent (14) linkages. (b) Cellulose, with (14) linkages, can adopt a fully extended conformation.23The Structure of Cellulose

Figure 7.24 The structure of cellulose, showing the hydrogen bonds (blue) between the sheets, which strengthen the structure.Intrachain H-bonds in red; interchain H-bonds in green.24How Do Ruminant Animals Digest Cellulose?

Figure 7.25 Giraffes, cattle, deer, and camels are ruminant animals that are able to metabolize cellulose, thanks to bacterial cellulase in the rumen, a large first compartment in the stomach of a ruminant.25Other Structural Polysaccharides Chitin found in the exoskeletons of crustaceans, insects and spiders, and cell walls of fungi It is similar to cellulose, but C-2s are N-acetylCellulose strands are parallel; chitins can be parallel or antiparallel

26Structures of cellulose, chitin and mannan

Figure 7.26 Like cellulose, chitin and mannan form extended ribbons and pack together efficiently, taking advantage of multiple hydrogen bonds.27Other Structural PolysaccharidesAlginates Ca2+-binding polymers in algae Agarose and agaropectin - galactose polymers Glycosaminoglycans - repeating disaccharides with amino sugars and negative charges28The Structure of Agarose in Solution

Figure 7.27 The favored conformation of agarose in water is a double helix with a threefold screw axis.Agarose, a component of agar obtained from marine red algae, is a chain of alternating D-galactose and 3,6-anhydro-L-galactose.Agarose gels are used in laboratories to separate biomolecules on the basis of size29

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