lecture 25 - Chapter 25. Biomolecules: Carbohydrates Based...

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Chapter 25. Biomolecules: Carbohydrates Based on McMurry’s Organic Chemistry , 7 th edition
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2 Importance of Carbohydrates Distributed widely in nature Key intermediates of metabolism (sugars) Structural components of plants (cellulose) Central to materials of industrial products: paper, lumber, fibers Key component of food sources: sugars, flour, vegetable fiber Contain OH groups on most carbons in linear chains or in rings
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3 Chemical Formula and Name Carbohydrates have roughly as many O’s as C’s (highly oxidized) Since H’s are about connected to each H and O the empirical formulas are roughly (C(H 2 O)) n Appears to be “carbon hydrate” from formula Current terminology: natural materials that contain many hydroxyls and other oxygen-containing groups
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4 Sources Glucose is produced in plants through photosynthesis from CO 2 and H 2 O Glucose is converted in plants to other small sugars and polymers (cellulose, starch) Dietary carbohydrates provide the major source of energy required by organisms
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5 Why this Chapter? To see what the structures and 1˚ biological functions of carbohydrates are To have an introduction on how carbohydrates are biosynthesized and degraded in organisms
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6 25.1 Classification of Carbohydrates Simple sugars (monosaccharides) can't be converted into smaller sugars by hydrolysis. Carbohydrates are made of two or more simple sugars connected as acetals (aldehyde and alcohol), oligosaccharides and polysaccharides Sucrose (table sugar): disaccharide from two monosaccharides (glucose linked to fructose), Cellulose is a polysaccharide of several thousand glucose units connected by acetal linkages (aldehyde and alcohol)
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7 Aldoses and Ketoses aldo - and keto - prefixes identify the nature of the carbonyl group - ose suffix designates a carbohydrate Number of C’s in the monosaccharide indicated by root (-tri-, tetra-, penta-, hexa-)
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8 25.2 Depicting Carbohydrate Stereochemistry: Fischer Projections Carbohydrates have multiple chirality centers and common sets of atoms A chirality center C is projected into the plane of the paper and other groups are horizontal or vertical lines Groups forward from paper are always in horizontal line. The oxidized end of the molecule is always higher on the page (“up”) The “projection” can be seen with molecular models
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Stereochemical Reference The reference compounds are the two enantiomers of glyceraldehyde, C 3 H 6 O 3 A compound is “D” if the hydroxyl group at the chirality center farthest from the oxidized end of the sugar is on the right or “L” if it is on the left. D
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lecture 25 - Chapter 25. Biomolecules: Carbohydrates Based...

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