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BCH Exm 3, Carb. - 1 g Carbohydrates 2 g Starch Chapter 16...

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1 g Carbohydrates Chapter 16, in Campbell, 5th ed. 2 g Starch and cellulose These are both polymers of the sugar monomer, glucose, and are found in plants. Together, they represent over half of all the organic carbon on earth. They differ in how the glucose monomers are joined together. Both are polysaccharides, long polymers of sugars. Short polymers are called "oligosaccharides". Glycogen is another sugar polymer, found in animals. 3 g Functions of polysaccharides Storage form of sugars. Source of energy, through catabolism. Important part of receptors on the cell surface. Involved in immune recognition. Extracellular structural components that support and protect cells. 4 g Monosaccharides (sugars) Most common in cells are the 6~carbon sugars. 5-carbon sugars are found in DNA and RNA. 4- and 7~carbon sugars take part in photosynthesis and other metabolic processes. Three~carbon sugars are called trioses; these are the simplest sugars. 4-carbon: tetroses; 5-carbon: pentoses; 6-carbon: hexoses; 7-carbon: heptoses; etc. 5 g Monosaccharides, cont. Types: Aldoses: polyhydroxy aldehyde Eg. glyceraldehyde Ketoses: polyhydroxy ketone Eg., dihydroxyacetone 6 g Stereoisomers 03 Sugars occur in two or more forms that are optical isomers. 03 Biochemists call the most common forms the D and L forms. 03 D~sugars predominate in biological systems. 03 Fig 16.4 shows that the number of possible different stereoisomers depends on the carbon chain length. 03 This figure shows only half of the possible isomers, the D-series. There is also an L- series. 03 Each L-form is an enantiomer to the D-form. 03 7 g Stereoisomers, cont. 8g 9 g Cyclic structures of sugars Linear sugars become circularized through interactions between different parts of the molecule. In this form, they resemble the cyclic molecules furan and pyran: 5-carbon sugars: furanoses. These are planar. 6-carbon sugars: pyranoses. These are folded like a chair (see fig. 16.7). 10 g Cyclic structures of sugars, cont 03 Biochemists usually show the circular structure as a Haworth Projection(see fig.
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16.8). The alternative is the Fischer projection, which carbons are linked via an oxygen residue.
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