For questions 1-4, match the carbohydrate with its size/functional group name:

Chemistry 11 Fall 2009 Examination #5 ANSWER KEY For the first portion of this exam, select the best answer choice for the questions below and mark the answers on your scantron. Then answer the free response questions that follow (100 pts. total; multiple choice 2 pts. each). For questions 1-4, match the carbohydrate with its size/functional group name: A. polysaccharide C. disaccharide B. monosaccharide, aldohexose D. monosaccharide, ketohexose 1. sucrose C 2. starch A 3. D-fructose D 4. maltose C 5. The order of amino acids in a peptide or protein A. is critical to its structure. B. is critical to its structure and function. C. is critical to its function. D. is critical to neither structure nor function. E. can be ignored as long as all the amino acids are present. 6. Which of the following about lipids is NT TRUE? A. Lipids are soluble in liquid ammonia. B. Lipids are classified based on their property of solubility rather than their structure. C. Lipids are soluble in CCl 4. D. Lipids form an integral part of the cell membrane. E. Lipids store energy within fat cells. 7. What is the result when a polysaccharide undergoes a hydrolysis reaction? A. The product is starch. B. The polysaccharide breaks down into smaller sugars. C. Two smaller sugars are joined to make a larger carbohydrate. D. The product forms Benedict s reagent. E. The products are generally glucose, fructose, and/or galactose.

8. At physiological p, the NET charge on an amino acid with no ionizable side chain is: A. +1 B. 0 C. +2 D. 1 E. 2 9. Which fatty acid has the highest expected melting point? A. 18:0 B. 16:0 C. 16:1 D. 18:2 E. 18:3 10. The term used in carbohydrate chemistry to describe a ring opening, closing, and interconverting between its anomeric forms is called: A. resonance B. a hemiacetal C. hydrolysis D. mutarotation E. a glycoside 11. Which functional group is involved in donating a proton to form the zwitterion in aqueous amino acid solutions? A. amine B. amide C. carboxylic acid D. peptide linkage E. amino acids exist as neutral un-ionized molecules 12. Soaps are: A. sodium or potassium salts of glycerol B. sodium salts of fatty acids C. derivatives of carbohydrates D. triglycerides E. made from hydrogenated oils

13. In its chair conformation, β-d-glucopyranose is the most widely occurring form of glucose in nature with the following characteristics EXCEPT: A. it forms a six-membered ring. B. carbon-6 is above the plane of the chair. C. all of the hydroxyl groups are equatorial. D. the anomeric carbon has a hydroxyl group that is below the plane of the chair. E. all axial positions are occupied by hydrogen. 14. Which of the following descriptions about amino acids is CRRECT? A. Amino acids are covalent compounds. B. Amino acids are ionic compounds. C. Amino acids are solids with low melting points. D. both B and C E. All the amino acids of all the proteins in the body are D-isomers. 15. Starch, sucrose and cellulose are all examples of: A. monosaccharides B. disaccharides C. polysaccharides D. reducing sugars E. non-reducing sugars 16. Fatty acids typically contain: A. 12 20 odd number of carbons with a carboxylic acid B. 12 20 even number of carbons with an ester C. branched carbon substituents that extend from the saturated or unsaturated main chain D. triple bonds surrounded by single bonds E. None of the above 17. Which of the following is an anomeric pair? A. D-glucose and L-glucose B. D-glucose and D-fructose C. α-d-glucose and β-d-glucose D. α -D-glucose and β-l-glucose E. D-glucose and L-fructose

18. The dipeptides Ser-Thr and Thr-Ser: A. are stereoisomers B. are constitutional isomers C. have different properties D. both A and C E. both B and C 19. The number of fatty acids that make up a triglyceride is/are: A. ne B. Two C. Three D. either A, B or C E. Fatty acids are not part of a triglyceride molecule. 20. uman beings don t have the enzymes necessary for the hydrolysis of the β (1 4) glycosidic linkages between molecules of glucose. That is why we cannot digest this compound, a component of certain laxatives. The compound described is: A. amylose B. glycogen C. cellulose D. lactose E. sucrose 21. The interaction that forms between the ionized side chains of amino acids with opposite charges is called: A. a salt bridge B. a hydrogen bond C. a hydrophobic interaction D. an α-helix E. an antiparallel β-pleated sheet 22. ydrogenation involves which of the following? A. removing hydrogen from fatty acids and forming more double bonds B. adding hydrogen to fatty acids and reducing double bonds C. raising the melting point of the fat or oil D. both A and C E. both B and C END F MULTIPLE CICE

23. (17 pts. total) This section involves a series of questions dealing with amino acids and proteins. A. (4 pts.) Amino acids are generally classified on the basis of their side-chain chemical properties. Your textbook classifies glycine as a polar amino acid when its side chain is nonpolar. Explain why. Glycine as a unit behaves like a polar amino acid as there is only a small amount of nonpolar character from the sidechain compared to the large influence of the α-amino and α-c groups. B. (2 pts.) Is it possible to have an enantiomer of glycine? If possible, draw the enantiomer and indicate if it is a D- or L- form. If not possible, indicate why glycine does not have an enantiomer. No because glycine does not contain a chiral center, which means it cannot possess an enantiomer. C. (5 pts.) Write the names of two amino acids that have more than one stereocenter? Draw the structures and indicate the stereocenters with an asterisk (*). The two amino acids are isoleucine and threonine as shown below: 3 N * * * C 3 N * C Isoleucine Threonine D. (6 pts.) In heavy metal poisoning, one of the antidotes prescribed is raw egg whites and milk. The type of noncovalent interaction formed between proteins in egg white and the heavy metal is -----S - g 2+ - S----- (where ----- represents the understood remainder of the protein chain). 1) (2 pts.) Identify the amino acid that is involved in this interaction. Cys 2) (2 pts.) What is this interaction called? metal-ion coordination 3) (2 pts.) Does this interaction affect the primary, secondary, tertiary, or quaternary structure of a protein? Briefly explain. This interaction affects the tertiary structure of a protein. (Refer to your course guide for descriptions of the 4 types of protein structure.)

24. (12 pts. total) Questions 24 and 25 involve carbohydrates. For #24 (A D), consider the hydrolysis of lactose. A. (5 pts.) Draw the structure of lactose. Does your drawing represent a reducing or non-reducing sugar? Make certain to draw all the possible anomers of your structure (if applicable). Reducing sugar because the cyclic hemiacetal of the D-glucopyranose unit is in equilibrium with its open-chain form and can be oxidized to a carboxyl group. C 2 C 2 C 2 C 2 + B. (2 pts.) What is the molecular formula for lactose? C 12 22 11 C. (1 pt.) Identify the products for the hydrolysis of lactose by drawing Fischer projections of the sugar(s) below. Can you name the sugar(s)? If so, label your drawing(s). D-galactose and D-glucose, shown respectively below: C C 2 C C 2 D. (4 pts.) FIGURE IT UT! Doctors use a lactose tolerance test to determine if a person is lactose intolerant. In this test, the person is given a solution of lactose to drink. Blood glucose concentration levels are then measured over the next two hours. A test was carried out on a healthy man who was lactose tolerant and on a man who was lactose intolerant. The results for the first hour are shown below:

Time in minutes Blood glucose concentration in mmol/l ealthy lactose tolerant man Lactose intolerant man 0 3.8 3.8 15 4.7 3.9 30 6.1 3.8 45 6.6 3.9 60 6.2 3.9 1) (2 pts.) The blood glucose concentration changed in the healthy man after he had taken the test. Describe how this can be the case using appropriate biochemical principles. The healthy man has an enzyme (i.e., lactase) that helps in the hydrolysis of lactose into D-glucose and D-galactose, thereby increasing the concentration of glucose in the blood. 2) (2 pts.) Now explain the results for the lactose intolerant man using appropriate biochemical principles. The lactose intolerant man lacks the enzyme lactase and therefore cannot break down lactose, resulting in a low glucose concentration. 25. (12 pts. total) Below is the structure of a carbohydrate. Answer all the questions that follow regarding this carbohydrate. Numbering labels of sugars do not necessarily imply linkage order. sugar 1 sugar 2 A. (1 pt.) Identify the type of linkage in the structure above. α (1 4) linkage B. (1 pt.) The covalent bond joining the two monosaccharides is known as what? Glycosidic bond

C. (4 pts.) Using your knowledge of organic chemistry, draw the MST STABLE chair conformation for each of the sugars present in this carbohydrate. Both sugars 1 and 2 are D-glucose as shown via the chair conformation below: C 2 D. (4 pts.) Convert each of the chair conformations to Fischer projections and name each of the sugars. Both sugars 1 and 2 are D-glucose as shown below: C C 2 E. (1 pt.) Is this carbohydrate a reducing or non-reducing sugar? Briefly explain your identification. Reducing sugar because the cyclic hemiacetal of the D- glucopyranose unit (sugar 2) is in equilibrium with its open-chain form and can be oxidized to a carboxyl group. F. (1 pt.) Finally, identify your carbohydrate based on your knowledge of structures taught to you in class. Maltose 26. LAST NE! (15 pts. total) A. (3 pts.) What is the difference between a fatty acid, a triglyceride, and a steroid? Appropriate detail should accompany your response in order to receive credit. Fatty acids consist of 12-20 even numbers of carbons (including a carboxylic acid) that are the building blocks of fat molecules. Three fatty acids combine with one glycerol to form a triglyceride. Steroids are compounds that contain a four ring generic structure. B. (6 pts.) Give an example of a triglyceride and a fatty acid molecule by drawing two structures using your knowledge of biochemistry. Also draw the structure of the steroid nucleus and name the most important steroid. An example of a fatty acid is C 3 (C 2 ) 14 C. Several examples possible here as long as the # of carbons is even with 12 20 carbons.

An example of a triglyceride is: C 2 C(C 2 ) 14 C 3 CC(C 2 ) 7 C=C(C 2 ) 7 C 3 C 2 C(C 2 ) 16 C 3 The structure of a steroid is: Most important steroid is cholesterol. C. (2 pts.) What is the other name for FAT? Name the functional group present in this molecule. Triglyceride. Ester functional groups link the glycerol to the fatty acids. D. (3 pts.) The reaction of a triglyceride with a strong base is called saponification and is of commercial importance in making soap. E. (1 pt.) The carriers of cholesterol are called lipoproteins.