A Getting-It-n Review and Self-Test arbohydrates arbohydrates, one of the three principal classes of foods, contain only three elements: (1), (2), and (3). The name carbohydrate is derived from the French hydrates de carbone because the empirical formula in many cases is (4). arbohydrates are actually aldehydes or ketones that contain many (5) groups. The simplest carbohydrates are glyceraldehyde and dihydroxy acetone. A classification system for carbohydrates is based on the number of units linked together. If there is only one unit, the carbohydrate is termed a (6). Two units linked together are a (7), such as sucrose, while long chain carbohydrates, such as glycogen and cellulose, are (8). The most common monosaccharide, (9), has (10) asymmetric carbon atoms. The number of isomers related to glucose is (11). All of these have been synthesized, but only D glucose and D galactose are of biological importance. Another common hexose, fructose, is a (12), and when linked to glucose, it forms the disaccharide (13). ther disaccharides are (14) and lactose which is known also as (15). All monosaccharides and most disaccharides are reducing sugars capable of reducing silver ions and copper ions. The only common sugar that is not a reducing sugar is the disaccharide (16). The hemiacetal structure of carbohydrates involves an alcohol linkage and a(n) (17) linkage on the same carbon atom. Acetal structures have (18) ether linkages to the same carbon. The hemiacetal or cylic form is unstable and hydrates easily to the open form, which can reform to the other diasteromer. The symbols used for the two forms are alpha ( ) and beta (19). Each of the diasteromers rotates polarized light and in solution there is an equilibrium between the forms. Diasteromers that differ in spatial arrangement only on 1 carbon are called (20). The switching back and forth from to forms is called (21) and occurs in hemiacetals but not (22). Glycosides such as cellulose and starch are only ether linkages and are therefore (23) structures and (24) exhibit mutarotation. Lactose and maltose undergo mutarotation, which means at least one of their monosaccharides has a (25) ring structure. Sucrose does not undergo mutarotation, which means only (26) or (27) linkages.
2 28. For each of the following carbohydrate molecules, pick out all of the correct descriptive terms from the list below that apply to the particular molecule. descriptive terms triose aldose reducing sugar D configuration tetrose ketose non-reducing sugar L configuration pentose hexose a. b. c. 2 2 2 2 d. e. f. 2 2 2 2 g. h. 2 2 2
3 29. Examine the carbohydrate formulas below and then answer the questions that follow. a. b. c. 2 2 d. e. 2 2 2 (1) Identify the pyranose and furanose ring structures. (2) Identify the Fisher projection, tree, and aworth formulas. (3) Identify the hemiacetal forms. (4) ow many carbons are there in the tree formula carbohydrate? (5) Identify (a) and (e) as either D and/or L. 30. Match the disaccharide in the left with their two constituent monsaccharides from the list on the right. disaccharides monosaccharides (1) sucrose glucose (2) lactose fructose (3) maltose galactose
4 31. Match a possible source from the right with the sugar listed on the left. sugar source source (1) glucose fruit juice honey (2) galactose sugar beets milk (3) fructose starch sugar cane (4) sucrose sucrose sprouting grain (5) lactose lactose agave (6) maltose pectin 32. Match the polysaccharide with the correct descriptive statement. (1) starch a. glucose units, -1,4 linkage, highly branched (2) cellulose b. fructose units, 1,2-linkage (3) glycogen c. glucose units, -1,4 linkage, moderately branched (4) inulin d. glucose units, -1,4 linkage 33. omplete the following reactions. a. R + 2 u +2 + + 3 2 What is the visual evidence of positive test b. Br 2 2 2
5 c. N 3 2 d. 2 2 Pt ANSWERS 1. carbon 2. oxygen 3. hydrogen 4. ( 2)n 5. hydroxy 6. monosaccharide 7. disaccharide 8. polysaccharides 9. glucose 10. four 11. Sixteen 12. ketose 13. sucrose 14. maltose 15. milk sugar 16. sucrose 17. ether 18. two 19. 20. Anomers 21. mutarotation 22. acetals 23. acetal 24. do not 25. hemiacetal 26. acetal 27. ether
6 28. a. triose, aldose, reducing, D b. pentose, ketose, nonreducing, D c. hexose, aldose, reducing, D d. hexose, ketose, reducing, D e. pentose, aldose, reducing, L f. pentose, aldose, reducing, D g. tetrose, ketose, reducing, L h. pentose, aldose, reducing, L 29. (1) b and c are pyranose, d is furanose (2) Fischer projections are b and e, tree formula is a, and aworth formulas are c and d (3) emiacetal forms are b, c, d (4) Tree formulas has six carbons, a hexose (5) a is D and e is D 30. (1) sucrose glucose & fructose (2) lactose glucose & galactose (3) maltose two glucose units 31. (1) glucose starch & sucrose (2) galactose lactose & pectin (3) fructose honey, sucrose, fruit juice, agave (4) sucrose sugar cane, sugar beets (5) lactose milk (6) maltose sprouting grain 32. (1) starch c (2) cellulose d (3) glycogen a (4) inulin b 33. a. b. _ R + u 2 The u 2 will be a brick-red precipitate 2 c. d. 2 2