2. Which of the following is NOT true about carbohydrates

Transcription

1 Chemistry 11 Fall 2011 Examination #5 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). 1. ydrolysis of a triglyceride molecule yields A. amino acids and water B. amino acids and glucose C. fatty acid and glycerol D. glucose and glycerol E. glycerol and water 2. Which of the following is NOT true about carbohydrates A. Cellulose and starch are examples of carbohydrates B. Carbohydrates are polyhydroxylated aldehydes or polyhydroxylated ketones C. Aldoses and ketoses are names associated with carbohydrates D. Carbohydrates act as storehouse of chemical energy E. All carbohydrates are reducing sugars 3. Which of the following single letter codes represents the structure below? A. DVYGSA B. ASGYVD C. EVFGSA D. ASGFVE E. EVGSAF 1

2 4. Cholesterol is an example of what type of lipid? A. triglyceride B. fat C. fatty acid D. steroid E. phospholipid 5. Which of the following is NOT a polysaccharide? A. glycogen B. starch C. amylase D. cellulose E. sucrose 6. Identify the strongest form of intermolecular bonding that could be formed involving the residue of the amino acid serine. A. ionic bond B. hydrogen bond C. London dispersion forces D. dipole-dipole E. covalent 7. In triacylglycerols, the fatty acid and glycerol are attached by which type of linkage? A. ether B. ester C. amide D. ketone E. none of the above 8. For the question below, fill in the blanks with the correct answer: Monosaccharides exist almost exclusively as cyclic, and a glycoside formed from a monosaccharide exists as a cyclic. A. acetals, hemiacetal B. pyranoses, furanose C. disaccharides, polysaccharide D. chairs, anomeric carbon E. hemiacetals, acetal 2

3 9. Which of the following statement about zwitterions is true? A. It is a neutral molecule B. It is a cation C. It is an anion D. It is a carbocation E. It is another word for net ionic 10. Identify the only correct statement among options A, B, C, D and E: The solubility of fatty acids in water increases as: A. The number of carbon atoms increases. B. The number of carbon atoms decreases, and the number of double bonds increases. C. The number of carbon atoms increases, and the number of double bonds decreases. D. The number of carbon atoms increases, and the number of double bonds increases. E. None of the options A, B, C, or D above applies. 11. Which of the following pairs is inter-converted in the process of mutarotation? A. α-d-glucose and β-d-glucose B. D-glucose and L-glucose C. D-glucose and D-fructose D. D-glucose and D-glucosamine E. α -D-glucopyranose and α -D-glucofuranose 12. The amino acid L-aspartic acid is called L because it A. is very little B. is a left-handed molecule C. is levorotatory (i.e., it rotates a plane of polarized light to the left) D. has the same absolute configuration about the chiral carbon as the most basic of the amino acids, L-glycine E. has the same absolute configuration about the chiral carbon as Lglyceraldehyde 13. Which of the fatty acids below is expected to have the highest melting point? A. Myristic acid (14:0) B. Palmitoleic acid (16:1) C. Oleic acid (18:1) D. Stearic acid (18:0) E. Lenolenic acid (18:3) 3

4 14. A sugar having an anomeric carbon that is not in a glycosidic bond is known as a A. monosaccharide B. reducing sugar C. non-reducing sugar D. semi-reducing sugar E. acetal 15. Which of the following statements is correct with respect to the amino acid composition of proteins? A. Proteins with the same molecular weight have the same amino acid composition. B. Proteins contain at least one each of the twenty different standard amino acids. C. Larger proteins have a more uniform distribution of amino acids than smaller proteins. D. Proteins with different functions usually differ significantly in their amino acid composition. E. The average molecular weight of an amino acid in a protein increases with the size of the protein. 16. Fatty acid double bonds almost always have the A. trans configuration B. cis configuration C. R configuration D. S configuration E. D configuration 17. Which of the following functional groups is necessary to react with an aldehyde or ketone to form a cyclic hemiacetal? A. another aldehyde B. another ketone C. an ester D. an alcohol E. all of the above 18. If the following section of a polypeptide is folded into an α-helix, to which amino acid is the carbonyl group of alanine noncovalently bonded? ala-ser-val-asp-glu-leu-gly A. serine B. glutamic acid 4

5 C. valine D. aspartic acid E. leucine 19. ow many carbon atoms are associated with the generic steroid structure? A. 15 B. 16 C. 17 D. 18 E Which of the following statements about glycogen, amylose, and amylopectin is false? A. All are homopolymers (repeating units) of glucose. B. Amylose is unbranched; amylopectin and glycogen contain many (α1 6) branches. C. All have glycosidic bonds. D. Amylose serves primarily as structural elements in plant cell walls. E. Glycogen is found in animals; amylose and amylopectin are found in plants. 21. Except for glycine, the side chains of nonpolar non acidic amino acids are best categorized: A. as ring structures B. as organic bases with a positive charge C. as organic acids with a negative charge D. as neutral hydrocarbon structures E. by the presence of a hydroxyl, carboxyl, or sulfur-containing group 22. The insolubility of lipids in water is best explained by which of the following? A. Lipids are polar molecules. B. The polar portion of lipids is much larger than the nonpolar portion. C. The polar portion of lipids is much smaller than the nonpolar portion. D. The polar and nonpolar portions of lipids are of comparable size. E. Lipids deliver chemical signals from one part of the body to another. For Questions 23 25, refer to the following sets of amino acids for the listed descriptions: A. Alanine and Glutamine B. Glutamate and Arginine C. Leucine and Valine 5

6 D. Serine and Tyrosine E. Proline and Glycine 23. Capable of forming a salt bridge B 24. Characterized by predominantly hydrophobic interactions C 25. Can form hydrogen bonds D 26. Which of the following is TRUE of the spacial distribution of the hydroxyl groups in β-d-glucopyranose? A. They are all in axial positions. B. They are all in equatorial positions. C. The hydroxyl on carbon-1 is axial; those remaining are equatorial. D. The hydroxyl on carbon-1 is equatorial; those remaining are axial. E. They have equal but opposite optical rotations. 27. Vegetable oil is made into margarine through: A. halogenation B. hydrohalogenation C. partial hydrogenation D. methylation E. oxidation 28. Which of the following amino acids have two chiral centers? A. threonine B. proline C. isoleucine D. A and B E. A and C For Questions 29 31, refer to the following answer choices for the listed descriptions: A. Primary protein structure B. Secondary protein structure C. Tertiary protein structure D. Quarternary protein structure E. None of the above 29. ydrogen bonding within the backbone B 30. ydrogen bonding between the side chains C 31. β-helix E 6

7 32. Carbohydrate: (14 points) A major cause of death in combat is an uncontrolled loss of blood. Chitosan has been used to make bandages that can stop blood flow. Chitosan, an amine of a monosaccharide you are familiar with, is obtained from shrimp shells. The structure of chitosan is given below. Answer all the questions that follow: A. (6 pts.) Chitosan is a polymer of a monosaccharide amine. What is this monosaccharide? Draw the Fischer projection of the monosaccharide amine. Monosaccharide amine is D-glucosamine O CO N 2 O O C 2 O B. (3 pts.) Indicate the type of glycosidic linkage that links each unit of the monosaccharide amine. β(1,4) glycosidic linkage C. (5 pts.) Apart from being an amine, chitosan resembles another polysaccharide in structure. What is the name of this polysaccharide? What is the main function of this polysaccharide? The name of the polysaccharide is cellulose. It is the skeletal polysaccharide of plants. 7

8 33. Lipids: (12 points) A. (2 pt.) Is the structure shown above a FATTY ACID, GLYCEROL, or a TRIGLYCERIDE? Circle the appropriate answer(s). Also circle the functional group or groups present and label the functional group(s). B. (8 pts.) Draw the structures of the products that are formed when the lipid shown above is hydrolyzed using each of the following solutions: 1. 2M 2 SO M NaO 8

9 B. (2 pts.) What is the term for the reaction with NaO in question B#2? What is the use of the product that is obtained in this reaction? Saponification; soap 34. Proteins: (12 points) A. (3 pts.) Draw the structure of a tripeptide made of threonine, arginine and methionine in that order. N-terminus C-terminus 3 N O O N S O N COO N N N 2 B. (2 pts.) Why do nurses and physicians use 70% alcohol to wipe the skin before giving injections? At a concentration of 70% alcohol, ethanol penetrates bacteria and kills them by coagulating their proteins, whereas 95% alcohol denatures only surface proteins. C. (4 pts.) Tell whether each of the following sentences describes the primary, secondary, tertiary or quartenary structure of a protein: 1. In the structure of insulin, arginine and glutamic acid form an ion pair. tertiary 2. Both parallel and antiparallel structures are possible. secondary 3. In collagen, the sequence of first six amino acids. primary 4. Four monomers combine to form hemoglobin. quaternary 9

10 D. (3 pts.) In a 6M urea solution, a protein that contained mostly antiparallel β-sheet became a random coil. Which groups and bonds were affected by urea? The intramolecular hydrogen bonds between the peptide backbone carbonyl group and the N- group. 10