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

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1 Chemistry 11 Fall 2013 Examination #5 PRACTICE 1 ANSWERS 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 B. monosaccharide, aldohexose C. disaccharide 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 1

2 D. the product is Benedict s reagent E. carbohydrates do not undergo hydrolysis 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 Which fatty acid has the highest 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 and closing constantly and going back and forth between its 3 conformations (open-chain, alpha, and beta) is called A. resonance B. hemiacetal C. hydrolysis D. mutarotation E. glycosidic bond 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. amino acids exist as neutral un-ionized molecules E. all of the above are incorrect 12. Soaps are A. sodium or potassium salts of glycerol B. sodium salts of fatty acids C. derivatives of carbohydrates D. a form of triglyceride E. made from hydrogenated oils 2

3 13. -D-glucopyranose in the chair form is the most widely occurring form of glucose in nature and it has the following characteristics EXCEPT A. forms a six-membered ring B. carbon 6 is above the plane of the chair C. all of the - groups are equatorial D. the anomeric carbon has a hydroxyl that is below the plane of the chair E. all axial positions are occupied by Which of the following 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 in all the proteins in the body are D-isomers 15. Starch, sucrose and cellulose are A. polysaccharides B. disaccharides C. reducing sugars D. non-reducing sugars E. monosaccharides 16. Common fatty acids have A. an odd number of carbons B. cyclic structures C. branched carbon chains D. double bonds separated 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 3

4 18. The dipeptides Gly-Ala and Ala-Gly A. are stereoisomers B. are constitutional isomers C. have different properties D. both A and C E. both B and C 19. Number of fatty acids that make up a triglyceride is A. ne B. Two C. Three D. Can be 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. The enzyme is a part of some laxatives. The compound 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. salt bridges B. hydrogen bonds C. hydrophobic interaction D. alpha helix E. disulfide bridges 22. ydrogenation A. Removes hydrogen from fatty acids and makes more double bonds B. Adds hydrogen to fatty acids and reduces double bonds C. Raises the melting point of the fat or oil D. Both A and C are correct E. Both B and C are correct END F MULTIPLE CICE 4

5 23. (17 pts. total). This section involves a series of questions dealing with amino acids and proteins. A. (4 points) Amino acids are usually 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- groups. B. (2 points) 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. In order for an amino acid to have D and L enantiomers, it must have an asymmetrical carbon atom (stereocenter), that is, one with four different groups bonded to it. Two of the groups on the α carbon of glycine are hydrogens. C. (5 points). Write the names of two amino acids that have more than one stereocenter? Draw the structures and indicate the stereocenters with an *. The two amino acids are Isoleucine and threonine. * * N 2 * N 2 * isoleucine threonine D. (6 points) In heavy metal poisoning, one of the antidotes prescribed is raw egg whites and milk. The type of non covalent interaction formed between protein in egg white and the heavy metal is S - g 2+ - S Identify the amino acids that are involved in this interaction? Two molecules of Cysteine. 2. What is this interaction called? 5

6 Metal ion coordination 3. Does this interaction affect the primary, secondary, tertiary, or quartenary structure of a protein? Tertiary structure of a protein 24. (12 points). Sections 24 and 25 involve questions on carbohydrates. Consider the hydrolysis of lactose. A. (5 points) Draw the structure of lactose. Does your drawing represent a reducing or non-reducing sugar? Finally, draw all the possible anomers of your structure if they exist. 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. -D-galactose unit C 2 C 2 hemiacetal of -D-glucose unit -D-galactose unit...r... C 2 C 2 hemiacetal of -D-glucose unit B. (2 points) What is the molecular formula for lactose? C

7 C. (1 point) Identify the products of hydrolysis of lactose. (structure not needed). D-galactose and D-glucose D. Doctors use a lactose tolerance test to find out if a person is lactose intolerant. In this test, the person is given a solution of lactose to drink. Blood glucose concentration is then measured over the next two hours. A lactose tolerance 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 in the table. Blood glucose concentration/mmol dm -3 Time/minutes ealthy lactose tolerant Lactose intolerant man man (2 points) The blood glucose concentration changed in the healthy man after he had taken the test. Describe how? The healthy man has the enzyme lactase that helps in the hydrolysis of lactose into glucose and galactose thereby increasing the concentration of glucose in the blood. 2. (2 points) Explain the results for the lactose intolerant man? The lactose intolerant man lacks the enzyme lactase and therefore cannot break down lactose into glucose and galactose and as a result the concentration of glucose in the blood is low 7

8 25. (12 points) Shown below is the structure of a carbohydrate. Answer all the questions that follow regarding this carbohydrate. Names of sugars do not necessarily imply linkage order. sugar 1 sugar 2 A. (1 points) What is the type of linkage in the above structure? α (1,4) linkage B. (1 point) The covalent bond joining the two monosaccharides is known as glycosidic bond C. (4 points) Using your knowledge of organic chemistry, draw the MST STABLE chair conformation for each of the sugars present in this carbohydrate. Sugar 1 Sugar 2 C 2 C 2 8

9 D. (4 points) Convert each of the chair conformations to Fischer projections and name each of your sugars. D-Glucose (sugar 1) D-Glucose (sugar 2) E. (1 points) Is this carbohydrate a reducing or non-reducing sugar? Why? 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 points) Finally, identify your carbohydrate based on your knowledge of structures taught to you in class. Maltose 25. LAST SECTIN! LIPIDS (15 points total) A. (3 points) What is the difference between a fat, fatty acid, and a steroid? Fatty acids are the building blocks of fat molecules Fat molecules are compounds made up of three fatty acids and one glycerol Steroids are compounds that contain a four ring generic structure 9

10 B. (6 points) Show an example of a fat molecule and a fatty acid molecule by drawing a structure using your knowledge of carboxylic acids. 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. Several examples possible here as long as the # of carbons is even An example of a fat molecule 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 Structure of a steroid Most important steroid is cholesterol C. (2 points) What is the other name for a fat molecule? Name the functional group present in this molecule. Triglyceride. Ester functional groups link the glycerol to the fatty acids D. (3 points) The reaction of a triglyceride with a strong base is called saponification and is of commercial importance in making soap. E. (1 point) The carriers of cholesterol are called lipoproteins. 10

11 ydrophobic nonacidic side chains 3 N Glycine Gly, G 3 C 3 N Alanine Ala, A 3 N Valine Val, V 3 N Leucine Leu, L 3 N Isoleucine Ile, I N 2 Proline Pro, P N 3 N Tryptophan Trp, W 3 N Phenylalanine Phe, F 3 CS 2 C 2 C 3 N Methionine Met, M ydrophobic acidic side chains 3 N ydrophilic nonacidic side chains 3 N 3 N ydrophilic acidic side chains 2 C 3 N Serine Ser, S S Aspartic acid Asp, D Threonine Thr, T 2 C Cysteine Cys, C 3 N Se 3 N 2 N 3 N Asparagine Asn, N Glutamic acid Glu, Q Selenocysteine Sec, U 2 N 3 N 3 N Glutamine Gln, Q Tyrosine Tyr, Y 2 N ydrophilic basic side chains 3 N 2 N N N 3 N N N 3 N Lysine Lys, K Arginine Arg, R istidine is, 11