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Chem 1152: Ch. 17

Chem 1152: Ch. 17. Carbohydrates. Introduction. Biomolecules: Organic compounds produced by living organisms Carbohydrates Lipids Proteins Nucleic acids. Functions of carbohydrates Provide energy through their oxidation Supply carbon for synthesis of cell components

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Chem 1152: Ch. 17

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  1. Chem 1152: Ch. 17 Carbohydrates

  2. Introduction Biomolecules: Organic compounds produced by living organisms • Carbohydrates • Lipids • Proteins • Nucleic acids Functions of carbohydrates • Provide energy through their oxidation • Supply carbon for synthesis of cell components • Serve as stored form of chemical energy • Form structural elements of some cells and tissues Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  3. Classes of Carbohydrates (saccharides) Hydrates of carbon Cm(H2O)n characterized by having multiple functional groups • Hydroxyl (alcohols) • Carbonyl (aldehydes or ketones) Mono- and disaccharides are simple sugars glucose fructose galactose ribose deoxyribose sucrose lactose starch glycogen cellulose chitin Fructo-oligosaccharides galactooligosaccharides Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011; http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/sugar.htm

  4. Stereochemistry of Carbohydrates Stereoisomerism: Isomeric molecules can have the same molecular formula and sequence of bonded atoms (constitution), but that differ in the three-dimensional orientations of their atoms in space. Enantiomers: Stereoisomers that are mirror images of each other. Chirality: “Handedness”. Refers to compounds that cannot be superimposed on mirror image. -Defined relative to central, chiral atom (carbon) enantiomers Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011; http://web.fccj.org/~ethall/stereo/stereo.htm

  5. Stereochemistry of Carbohydrates Chiral Carbon: Carbon in organic compound that has four different groups attached to it. Chirality: “Handedness”. Refers to compounds that cannot be superimposed on mirror image. Chiral carbon H H OHC OH C HO CHO C CHO indicates aldehyde CH2OH CH2OH OHC HO OH CHO C C CH2OH CH2OH enantiomers Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  6. Identify Chiral Carbons H OHCCHOH OHC OH C * CH2OH CH2OH CH3CCH2CH3 O CH3CHCH3 OH CH3CHCH2CH3 OH

  7. Identify chiral carbons in glucose H O C 1 C H OH 2 C HO H 3 H C OH 4 H C OH 5 CH2 OH 6 glucose

  8. chiral carbons in glucose Max # of possible stereoisomers = 2n where n = number of chiral carbon atoms p. 528 Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  9. Fischer Projections • Chiral Carbons represented by intersection of two lines • For fischer projections the prefixes (L-) and (D-) do not indicate Levorotatory (L-) and Dextrorotatory (D-) related to rotation of polarized light, but represent orientation of functional groups when compared to glyceraldehyde Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  10. Fischer Projections • When carbonyl is up: • D-family: OH (or NH2) group of chiral C most distant from anomeric center projects to right • L-family: OH (or NH2) group of chiral C most distant from anomeric center projects to left • Anomeric center: Carbonyl (aldehyde or ketone) carbon • Biological systems can only utilize the D- isomers. * * * * * * * * * * * * Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  11. Monosaccharides • Contain single polyhydroxy aldehyde or ketone unit • Further classified based on number of C atoms • Aldehydes contain prefix aldo-, ketones have prefix keto- Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  12. Monosaccharides: D- aldoses Chiral C’s? stereoisomers 2 1 4 2 8 3 16 4 Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  13. Monosaccharides: Chemical Properties • Because aldehydes and ketones react with alcohols to form hemiacetals and hemiketals, all monosaccharides with at least 5 carbon atoms exist predominantly in cyclic forms. • These are depicted using Haworth structures • Ring is drawn with oxygen to the back, and anomeric carbon to the right. • Furanose ring: A 5-member ring containing an oxygen atom. • Pyranose ring: A 6-member ring containing an oxygen atom. Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  14. Glucose (Blood Sugar) • Primary source of energy in cells • Precursor for Vitamin C synthesis • Modified subunits can form long polymer chains • starch, cellulose, glycogen 0.02% 64% 36% Hemiacetal (on C1) • Beta-hydroxy group: OH attached to anomeric carbon above ring. • Alpha-hydroxy group: OH attached to anomeric carbon below ring. Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  15. Fructose • Fruit sugar • Absorbed directly into bloodstream during digestion (like glucose and galactose) • Anomeric carbon is C2 1 2 22% 3 4 5 6 70% Hemiketal (on C2) http://upload.wikimedia.org/wikipedia/commons/1/1e/Fructose-isomers.jpg

  16. Chemical Reactions of Sugars • Open chain forms of monosaccharides (aldehydes, hydroxyketones) can be readily oxidized. • Ex. Use of Benedict’s reagent to oxidize aldehydes and ketones with hydroxy group on adjacent carbon. • At the same time, the cyclic forms are converted to open-chain forms and also react. • Reducing sugars: Monosaccharides that can be oxidized • Oxidation of carbohydrates to CO2 and H2O very important at cellular level, serves as source of heat and energy. Reducing sugar + Cu(II)  oxidized cmpd + Cu2O Deep blue solution Red-orange precipitate Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  17. Other Important Monosaccharides Ribose and Deoxyribose • Used to synthesize RNA and DNA • Used in protein synthesis Phosphodiester bond Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011: http://www.istpace.org/Web_Final_Report/WP_4_chem_subsystems/descr_chem_subsystems/pna_intro/pna_intro.html

  18. Other Important Monosaccharides Galactose • Synthesized in mammary gland, incorporated into milk lactose • Component of the antigens present on blood cells that determine blood type Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  19. Joining Monosaccharides • Monosaccharide units can be joined together by glycosidic linkages. • Glycosidic linkages are same as adding alcohol to hemi- intermediates Hemiacetal intermediate acetal Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  20. Polymerization of Monosaccharide Subunits • Through glycosidic linkages at the hemiacetal carbons, many monosaccharide subunits can be put together to form long, branching chains via 1,4 or 1,6 linkages. • These can be between 2 α, 2 β, or between an α and a β.

  21. Disaccharides Maltose Lactose Sucrose Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  22. Properties of Polysaccharides Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

  23. Plant starches • Components of plant starch built from glucose residues. Amylose (10-20%) No branching Amylopectin (80-90%) Branching 24-30 residues

  24. Structure of glycogen • Polymer built from glucose subunits. • Glucose in Glycogen are connected via α-1,4 or α-1,6 linkage. • α-1,4 linkage makes a linear chain, α-1,6 linkage makes a branch (~every 10 residues). • The end glucose residues without open 1’-OH is called nonreducing ends. • Branches provide more non-reducing ends for rapid degradation.

  25. What is glycogen and why do we need it? • Long-term energy reservoir for glucose in animal and fungal cells. • Found primarily in muscle and liver cells. • Liver produces glycogen for needs of organism, while muscle takes care of only itself. • Glycogen not as energy rich as fatty acids, and is used differently. • Controlled breakdown of glycogen and glucose release maintain blood-glucose levels. • Glucose is the primary fuel used by the brain. • Unlike fatty acids, glucose from glycogen is readily mobilized and can provide energy for sudden, strenuous activity.

  26. Cellulose • Most important structural polysaccharide and single most abundant organic compound on earth. • Provides strength and rigidity to plant cell walls. • Wood is ~50% cellulose. • Contains 300-3000 glucose subunits. • Form extended straight chains that hydrogen bond with parallel chains, creating long, rigid fibers. • Undigestible by humans.

  27. Intramolecular addition of alcohols to aldehyde H O C CH2OH 1 6 * H OH C H OH O C 5 2 H C HO H C C 1 OH H 4 3 H C OH C C 4 3 2 OH H H C OH 5 H OH CH2 OH 6 Intramolecularhemiacetal glucose • C1 is hemiacetal carbon. • Attached to it you will find: H, OH, OR and R, just like non-cyclical compounds.

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