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BIO152H5 (140)
Chapter 5

Chapter 5.odt

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Fiona Rawle

Chapter 5 Key Concepts • Sugars and other carbohydrates are highly variable in structure • Mono-saccharides are monomers that polymerize to form polymers called polysaccharides, via different types of glycosidic linkages. • Carbohydrates perform a wide variety of functions in cells, ranging from energy storage to formation of tough structural fibers. Mono-saccharides Vary in Structure 1. Location of the carbonyl group. • Aldose: The carbonyl is at the end of the monosaccharide. • Ketose: The carbonyl is in the middle of the sugar’s carbon chain. 2. Number of carbon atoms present. • Triose: three • Pentose: five • Hexose: six 3. Spatial arrangement of their atoms. • Different arrangement of the hydroxyl groups. The Structure of Polysaccharides • Polysaccharides are polymers that form from monosaccharides through a condensation reaction between two hydroxyl groups to create a glycosidic linkage. 1. The monomers joined by glycosidic linkages can be identical or different. 2. The glycosidic linkages can form between any two hydroxyl groups; so the location and geometry of these bonds vary widely. What Do Carbohydrates Do? • Carbohydrates are important building blocks in the synthesis of other molecules. • They indicate cell identity. • They store chemical energy. • They provide cells with fibrous structural materials. Glycoproteins: Cell Identity • Although polysaccharides are unable to store information, they do display information on the outer surface of cells in the form of glycoproteins—proteins joined to carbohydrates by covalent bonds. • Glycoproteins are key molecules in cell-cell recognition and cell-cell signalling. Starch and Glycogen: Storage Polysaccharides • Plants store sugars as starch, which is made of many α-glucose monomers joined by α-1,4- glycosidic linkages. This causes the monomer chain to form a helix.Animals store sugars as glycogen. • Starch can be branched (amylose) or unbranched (amylopectin). Glycogen is highly branched. • Branching occurs when glycosidic linkages form between carbon 1 of a glucose monomer on one strand and carbon 6 of a glucose monomer on another strand. Carbohydrates and Free Energy • In chemical evolution, the kinetic energy of sunlight and heat were converted into chemical energystored in the bonds of H2CO and HCN. • Today, most sugars are produced via photosynthesis [CO2 + H2O + sunlight ® (CH2O)n + O2], a key process that
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