Sp14 9Carbohydrates

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    MO figure

    Carbohydrates

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    Topics Covered in this Module

    Diversity of Structure and Function in Carbohydrate Molecules

    Polysaccharides

    Major Objectives of this Module

    Classify monosaccharides based on molecular characteristics.

    Relate structures of polysaccharides to their functions in cells and

    organisms.

    Understand how monosaccharides are classified based on molecular

    characteristics.Explain how a glycosidic linkage forms by a dehydration synthesis

    reaction.

    Classify monosaccharides based on molecular characteristics.

    Relate structures of polysaccharides to their functions in cells andorganisms.

    Understand how monosaccharides are classified based on molecular

    characteristics.

    Explain how a glycosidic linkage forms by a dehydration synthesis

    reaction.

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    Polymer - A high molecular weight compound consisting oflong chains that may be open, closed, linear, branched, orcross-linked.

    The chains are composed of repeating units, called

    monomers, which may be identical or different.

    Macromolecules are Polymers

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    HO

    HO

    Polymerization is a dehydration reaction: monomer in,

    water out

    HO

    H

    OH+ Water

    H

    Monomer

    Monomer

    H

    H

    OHH

    Monomer

    MonomerHO+

    H

    HO

    HO

    H

    H

    Water

    Depolymerization is a hydrolysis reaction: water in, monomer out

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    Carbohydrates are commonly classified on the basis oftheir size.

    Monosaccharides

    Disaccharides (2) Oligosaccharides (3-10)

    Polysaccharides (many)

    Carbohydrate = carbon hydrate or hydrated carbon atoms.

    One carbonyl (C=O), many hydroxyls.

    Classification of Carbohydrates

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    LE 5-3Triose sugars

    (C3H6O3)

    Glyceraldehyde

    Pentosesugars

    (C5H10O5)

    Ribose

    Hexose sugars (8 types)

    (C6H12O6)

    Glucose Galactose

    Dihydroxyacetone

    RibuloseFructose

    Aldehyde: carbonyl carbon (C=O) is terminal

    Ketone: carbonyl carbon (C=O) is internal

    Ps

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    Figure 1c

    General empirical formula for carbohydrates = (CH2O)n.

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    Figure 1d

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    Figure 5

    Disaccharides form by

    dehydration synthesis. The

    covalent bond is called aglycosidic linkage, the #s

    refer to the carbons

    involved.

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    Polysaccharides, the polymers of sugars, can be either

    structural molecules (cellulose) or energy storage

    molecules (amylose, amylopectin, glycogen)

    The structure and function of a polysaccharide are

    determined by its sugar monomers and the positionsof glycosidic linkages

    Polysaccharides

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    Amylose - The form of starch that is composed of long, (thousands)

    unbranched chains of glucose units which are joined by means of

    (1-4) glycosidic bonds.

    Amylopectin - The form of starch that is composed of long, branched

    chains of glucose units which are joined by means of (1-4) and (1-

    6) glycosidic bonds. Branching =~ 1 in every 30 monomers.

    Glycogen - A highly branched homopolysaccharide of D-glucose units

    that is the major form of storage of carbohydrate in animals (ie in

    liver and muscle); the glucose units are linked by means of (1-4) and

    (1-6) glycosidic bonds. Branching =~ 1 in every 10 monomers

    Energy Storage Polysaccharides

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    Figure 10b

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    Figure 10c

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    Figure 7

    Glycogen granules in mouse liver, starch granules in plant

    chloroplast. Glycogen and starch are energy storagepolysaccharides composed of glucose

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    Structural Polysaccharides: Cellulose

    Branch-free linear structure.

    Linear chain of several hundreds or thousands of beta

    glucose monomers.

    Allow hydrogen bonding to occur between adjacentcellulose molecules.

    Result in strong, parallel groupings of molecules called

    microfibrils. May be the most abundant organic compound on Earth.

    Primary component of tough walls that enclose plant cells.

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    Figure 10a

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    Enzymes that digest starch by hydrolyzing alpha linkages cant

    hydrolyze beta linkages in cellulose

    Cellulose in human food passes through the digestive tract as

    insoluble fiber

    Some microbes use enzymes to digest cellulose

    Many herbivores, from cows to termites, have symbiotic

    relationships with these microbes

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    Summary

    OBJECTIVE Classify monosaccharides based on molecular characteristics.

    Carbohydrates are organic compounds that include a carbonyl group and several

    hydroxyl groups. Based on their number of constituent monomers, carbohydrates

    are classified into monosaccharides, disaccharides, oligosaccharides, andpolysaccharides. Monosaccharides are further classified based on three main

    characteristics, including

    the location of their carbonyl group

    the length of their carbon skeleton, which is most often between three and seven

    carbon atoms

    the spatial arrangement of hydroxyl groups around asymmetric carbons

    OBJECTIVE Explain how a glycosidic linkage forms by a dehydration synthesis

    reaction.

    Glycosidic linkages form through dehydration synthesis reactions, which have a

    water molecule as a by-product. In this type of reaction, two monosaccharides

    form a covalent bond by giving up a water molecule and result in a disaccharide.

    This process can continue when many monosaccharides polymerize to form

    polysaccharides. The covalent bond formed between two monosaccharides is

    called a glycosidic linkage. The type of constituent monomers and the glycosidic

    bonds that make up the structure dictate the structure and function of

    polysaccharides.

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    OBJECTIVE Relate structures of polysaccharides to their functions in cells and

    organisms.

    Organisms use a diversity of polysaccharides for energy storage, structural

    support, cellular identity purposes, and synthesis of other molecules. The most

    common polysaccharides include starch, glycogen, cellulose, chitin, andpeptidoglycan. Carbohydrates have important functions in cells. These functions

    are related to the structures of the associated molecules. Starch and glycogen

    serve as energy-storage molecules in plants and animals, respectively. These

    molecules are composed of glucose monomers joined by 14 glycosidic linkages.

    The alpha () form of the glucose monomers makes these polysaccharides

    relatively accessible for energy supply. Cellulose, chitin, and peptidoglycan providestructural support to various organisms. These macromolecules include

    monosaccharides joined by 14 glycosidic linkages, which makes them more

    difficult to degrade. Oligosaccharides, unique combinations of about 210

    monosaccharides, are located on cell-surface glycoproteins. They function to

    communicate a cells type or species.