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Chemistry LibreTexts

25.9 Polysaccharides and Their Synthesis

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  • Objectives

    After completing this section, you should be able to

    1. identify the structural difference between cellulose and the cold‑water‑insoluble fraction of starch (amylose), and identify both of these substances as containing many glucose molecules joined by 1,4′‑glycoside links.
    2. identify the cold‑water‑soluble fraction of starch (amylopectin) as having a more complex structure than amylose because of the existence of 1,6′‑glycoside links in addition to the 1,4′‑links.
    3. compare and contrast the structures and uses of starch, glycogen and cellulose.

    Key Terms

    Make certain that you can define, and use in context, the key terms below.

    • amylopectin
    • amylose
    • polysaccharide

    Learning Objectives

    • To compare and contrast the structures and uses of starch, glycogen, and cellulose.

    The polysaccharides are the most abundant carbohydrates in nature and serve a variety of functions, such as energy storage or as components of plant cell walls. Polysaccharides are very large polymers composed of tens to thousands of monosaccharides joined together by glycosidic linkages. The three most abundant polysaccharides are starch, glycogen, and cellulose. These three are referred to as homopolymers because each yields only one type of monosaccharide (glucose) after complete hydrolysis. Heteropolymers may contain sugar acids, amino sugars, or noncarbohydrate substances in addition to monosaccharides. Heteropolymers are common in nature (gums, pectins, and other substances) but will not be discussed further in this textbook. The polysaccharides are nonreducing carbohydrates, are not sweet tasting, and do not undergo mutarotation.

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