Prentice Hall c2002Chapter 81 Principles of BIOCHEMISTRY Third Edition HORTON MORAN OCHS RAWN SCRIMGEOUR

Prentice Hall c2002Chapter 82 Chapter 8 - Carbohydrates Carbohydrates (“hydrate of carbon”) have empirical formulas of (CH 2 O) n, where n ≥ 3 Monosaccharides one monomeric unit Oligosaccharides ~2-20 monosaccharides Polysaccharides > 20 monosaccharides Glycoconjugates linked to proteins or lipids

Prentice Hall c2002Chapter Most Monosaccharides are Chiral Compounds Aldoses - polyhydroxy aldehydes Ketoses - polyhydroxy ketones Most oxidized carbon: aldoses C-1, ketoses usually C-2 Trioses (3 carbon sugars) are the smallest monsaccharides

Prentice Hall c2002Chapter 84 Aldoses and ketoses Aldehyde C-1 is drawn at the top of a Fischer projection Glyceraldehyde (aldotriose) is chiral (C-2 carbon has 4 different groups attached to it) Dihydroxyacetone (ketotriose) does not have an asymmetric or chiral carbon and is not a chiral compound

Prentice Hall c2002Chapter 85 Fig 8.1 Fischer projections of: (a) L- and D- glyceraldehyde, (b) dihydroxyacetone

Prentice Hall c2002Chapter 86 Fig 8.2 Stereo view of L- and D-glyceraldehyde (L)(D)

Prentice Hall c2002Chapter 87 Fig 8.3 Fisher projections of 3 to 6 carbon D-aldoses D-sugars have the same configuration as D-glyceraldehyde in their chiral carbon most distant from the carbonyl carbon Aldoses shown in blue (next slide) are most important in biochemistry

Prentice Hall c2002Chapter 88 Fig. 8.3

Prentice Hall c2002Chapter 89 Fig. 8.3 (continued)

Prentice Hall c2002Chapter 810 Fig 8.3 (continued)

Prentice Hall c2002Chapter 811 Enantiomers and epimers D-Sugars predominate in nature Enantiomers - pairs of D-sugars and L-sugars Epimers - sugars that differ at only one of several chiral centers Example: D-galactose is an epimer of D-glucose at C-4

Prentice Hall c2002Chapter 812 Fig 8.4 Fisher projections of L- and D-glucose

Prentice Hall c2002Chapter 813 Fig 8.5 Fisher projections of the 3 to 6 carbon D-ketoses (blue structures are most common)

Prentice Hall c2002Chapter 814 Fig. 8.5 (continued)

Prentice Hall c2002Chapter 815 Fig 8.5 (continued)

Prentice Hall c2002Chapter Cyclization of Aldoses and Ketoses Fig. 8.6 Reaction of an alcohol with: (a) An aldehyde to form a hemiacetal (b) A ketone to form a hemiketal

Prentice Hall c2002Chapter 817 Fig 8.7 (a) Pyran and (b) furan ring systems (a) Six-membered sugar ring is a “pyranose” (b) Five-membered sugar ring is a “furanose”

Prentice Hall c2002Chapter 818 Fig 8.8 Cyclization of D-glucose to form glycopyranose Fischer projection (top left) Three- dimensional figure (top right) C-5 hydroxyl close to aldehylde group (lower left)

Prentice Hall c2002Chapter 819 Fig. 8.8 (continued) Reaction of C-5 hydroxyl with one side of C-1 gives , reaction with the other side gives 

Prentice Hall c2002Chapter 820 Fig 8.9 Cyclization of D-ribose to form  - and  -D-ribopyranose and  - and  -D-ribofuranose Continued on next slide

Prentice Hall c2002Chapter 821 Fig. 8.9 (continued) Continued next slide

Prentice Hall c2002Chapter 822 Fig 8.9 (continued)

Prentice Hall c2002Chapter Conformations of Monosaccharides Fig Conformations of  -D-ribofuranose

Prentice Hall c2002Chapter 824 Fig 8.11 Conformations of  -D-glucopyranose (b) Stereo view of chair (left), boat (right) Haworth projectionChair conformation Boat conformation

Prentice Hall c2002Chapter 825 Fig 8.12 Conformations of  -D-glucopyranose Top conformer is more stable because it has the bulky hydroxyl substituents in equatorial positions (less steric strain)

Prentice Hall c2002Chapter Derivatives of Monosaccharides Many sugar derivatives are found in biological systems Some are part of monosaccharides, oligosaccharides or polysaccharides These include sugar phosphates, deoxy and amino sugars, sugar alcohols and acids

Prentice Hall c2002Chapter 827 Table 8.1

Prentice Hall c2002Chapter 828 A. Sugar Phosphates Fig 8.13 Some important sugar phosphates

Prentice Hall c2002Chapter 829 B. Deoxy Sugars In deoxy sugars an H replaces an OH Fig 8.14 Deoxy sugars

Prentice Hall c2002Chapter 830 C. Amino Sugars An amino group replaces a monosaccharide OH Amino group is sometimes acetylated Amino sugars of glucose and galactose occur commonly in glycoconjugates

Prentice Hall c2002Chapter 831 Fig 8.15 Several amino sugars Amino and acetylamino groups are shown in red

Prentice Hall c2002Chapter 832 Fig (continued)

Prentice Hall c2002Chapter 833 D. Sugar Alcohols (polyhydroxy alcohols) Sugar alcohols: carbonyl oxygen is reduced Fig 8.16 Several sugar alcohols

Prentice Hall c2002Chapter 834 E. Sugar Acids Sugar acids are carboxylic acids Produced from aldoses by: (1) Oxidation of C-1 to yield an aldonic acid (2) Oxidation of the highest-numbered carbon to an alduronic acid

Prentice Hall c2002Chapter 835 Fig 8.17 Sugar acids derived from glucose

Prentice Hall c2002Chapter 836 Fig (continued)

Prentice Hall c2002Chapter 837 F. Ascorbic Acid (Vitamin C) L-Ascorbic acid is derived from D-glucuronate Fig 8.18 L-Ascorbic acid

Prentice Hall c2002Chapter Disaccharides and Other Glycosides Glycosidic bond - primary structural linkage in all polymers of monosaccharides An acetal linkage - the anomeric sugar carbon is condensed with an alcohol, amine or thiol Glucosides - glucose provides the anomeric carbon

Prentice Hall c2002Chapter 839 Fig 8.19 Glucopyranose + methanol yields a glycoside

Prentice Hall c2002Chapter 840 A. Structures of Disaccharides Fig 8.20 Structures of (a) maltose, (b) cellobiose

Prentice Hall c2002Chapter 841 Fig (continued) Structures of (c) lactose, (d) sucrose

Prentice Hall c2002Chapter 842 B. Reducing and Nonreducing Sugars Monosaccharides and most disaccharides are hemiacetals (contain a reactive carbonyl group) Called reducing sugars because they can reduce metal ions (Cu 2+, Ag + ) Examples: glucose, maltose, cellobiose, lactose

Prentice Hall c2002Chapter 843 C. Nucleosides and Other Glycosides Anomeric carbons of sugars can form glycosidic linkages with alcohols, amines and thiols Aglycones are the groups attached to the anomeric sugar carbon N-Glycosides - nucleosides attached via a ring nitrogen in a glycosidic linkage

Prentice Hall c2002Chapter 844 Fig 8.21 Structures of three glycosides

Prentice Hall c2002Chapter Polysaccharides Homoglycans - homopolysaccharides containing only one type of monosaccharide Heteroglycans - heteropolysaccharides containing residues of more than one type of monosaccharide Lengths and compositions of a polysaccharide may vary within a population of these molecules

Prentice Hall c2002Chapter 846

Prentice Hall c2002Chapter 847 A. Starch and Glycogen D-Glucose is stored intracellularly in polymeric forms Plants and fungi - starch Animals - glycogen Starch is a mixture of amylose (unbranched) and amylopectin (branched)

Prentice Hall c2002Chapter 848 Fig 8.22 Structure of amylose (a) Amylose is a linear polymer (b) Assumes a left-handed helical conformation in water

Prentice Hall c2002Chapter 849 Fig 8.23 Structure of amylopectin

Prentice Hall c2002Chapter 850 Fig 8.24 Action of  - and  -amylase on amylopectin  -Amylase cleaves random internal  -(1-4) glucosidic bonds  -Amylase acts on nonreducing ends

Prentice Hall c2002Chapter 851 B. Cellulose and Chitin Fig 8.25 Structure of cellulose (a) Chair conformation (b) Haworth projection

Prentice Hall c2002Chapter 852 Fig 8.26 Stereo view of cellulose fibrils Intra- and interchain H-bonding gives strength

Prentice Hall c2002Chapter 853 Fig 8.27 Structure of chitin Repeating units of  -(1-4)GlcNAc residues

Prentice Hall c2002Chapter Glycoconjugates Heteroglycans appear in three types of glycoconjugates: Proteoglycans Peptidoglycans Glycoproteins

Prentice Hall c2002Chapter 855 A. Proteoglycans Proteoglycans - glycosaminoglycan-protein complexes Glycosaminoglycans - unbranched heteroglycans of repeating disaccharides (many sulfated hydroxyl and amino groups) Disaccharide components include: (1) amino sugar (D-galactosamine or D-glucosamine), (2) an alduronic acid

Prentice Hall c2002Chapter 856 Fig 8.28 Repeating disaccharide of hyaluronic acid GlcUA = D-glucuronate GlcNAc= N-acetylglucosamine

Prentice Hall c2002Chapter 857 Fig 8.29 Proteoglycan aggregate of cartilage

Prentice Hall c2002Chapter 858 B. Peptidoglycans Peptidoglycans - heteroglycan chains linked to peptides Major component of bacterial cell walls Heteroglycan composed of alternating GlcNAc and N-acetylmuramic acid (MurNAc)  -(1 4) linkages connect the units

Prentice Hall c2002Chapter 859 Fig 8.30 Glycan moiety of peptidoglycan

Prentice Hall c2002Chapter 860 Fig 8.31 Structure of the peptidoglycan of S. aureus (a) Repeating disaccharide unit, (b) Cross-linking of the peptidoglycan macromolecule (to tetrapeptide, next slide)

Prentice Hall c2002Chapter 861 Fig (continued) (to disaccharide, previous slide)

Prentice Hall c2002Chapter 862 Penicillin inhibits a transpeptidase involved in bacterial cell wall formation Fig 8.32 Structures of penicillin and -D-Ala-D-Ala Penicillin structure resembling -D-Ala- D-Ala is shown in red

Prentice Hall c2002Chapter 863 C. Glycoproteins Proteins that contain covalently-bound oligosaccharides O-Glycosidic and N-glycosidic linkages Oligosaccharide chains exhibit great variability in sugar sequence and composition Glycoforms - proteins with identical amino acid sequences but different oligosaccharide chain composition

Prentice Hall c2002Chapter 864 Four subclasses of O-glycosidic linkages (1) GalNAc-Ser/Thr (most common) (2) 5-Hydroxylysine (Hyl) to D-galactose (unique to collagen) (3) Gal-Gal-Xyl-Ser-core protein (4) GlcNAc to a single serine or threonine

Prentice Hall c2002Chapter 865 Fig O-Glycosidic and N-glycosidic linkages

Prentice Hall c2002Chapter 866 Fig 8.34 Four subclasses of O-glycosidic linkages

Prentice Hall c2002Chapter 867 Fig 8.35 Structures of N-linked oligosaccharides

Prentice Hall c2002Chapter 868 Fig (continued)