PHAR3316 Pharmacy biochemistry Exam #2 Fall 2010 KEY

Transcription

1 1. How many protons is(are) lost when the amino acid Asparagine is titrated from its fully protonated state to a fully deprotonated state? A. 0 B. 1 * C. 2 D. 3 E. none Correct Answer: C (this question asks about the amino acid this means NH2 COOH only since the side chain is not titratable I gave the points to the whole class and those who got it right also got extra points 2. Which pair of amino acids have aromatic characteristics? A. Threonine &Tyrosine * B. Tryptophan & Histidine C. Methionine & Tryptophan D. Phenylalanine & Lysine E. Phenylalanine & Proline Correct Answer: B 3. What type of moleculear interaction is essential in the formation of the protein secondary structures, alpha helices and beta sheets? * A. hydrogen bond B. Ionic C. Induced dipole D. Van-de-Waals E. Covalent

2 4. What is(are) the single bond(s) that make up the backbone of a peptide and responsible for its flexibility? I-C(alpha)-N II-N-C=O III-C(alpha)-C=O * A. I and III B. I and II C. II and II D. I only E. II only 5. Around what ph is the amino acid Isoleucine predominately a neutral species with a net charge of 0? Use panel A as a reference for pka's A. 2 B. 3 * C. 5 D. 8 E. 10 Correct Answer: C 6. Refer to panel B. What is the point where ph=pka of the carboxyle group of the amino acid being titrated? A. I B. II C. III * D. V E. VI

3 7. Refer to panel B. What is/are the point(s) where the amino acid being titrated can act as a buffer? A. I, II, V B. II, IV C. I, II, III, IV * D. V, VI, VII E. II only 8. The beta-strand structure of a protein can be considered an example of: A. Primary structure * B. Secondary structure C. Tertiary structure D. Quartenary structure E. None of the options given are correct. Correct Answer: B 9. What characteristics below can be associated hemoglobin? A. The protein inteface contains histidine residues that are affected by the hydrogen ion concentration B. Subunit-subunit interactions are critical to its allosteric properties C. high BPG concentration, high partial preassure of CO2 and high temperatures all reduce the percent oxygen saturation D. The subunits contain a hydrophobic pocket that bind the heme group * E. All of the statements listed are charateristics of hemoglobin Correct Answer: E 10. What is the name of the amino acid in panel C. A. Alanine B. Lysine C. Isoleucine D. Asparagine * E. Leucine Correct Answer: E

4 11. Which of the following amino acids have R-groups capable of engaging in hydrogen bond interactions? A. Alanine, Leucine and Glycine B. Lysine, Histidine and Valine C. Aspartic acid, Isoleucine and Tyrosine D. Glutamic acid, Isoleucine and Proline * E. Glutamine, Serine and Threonine Correct Answer: E 12. The key explanation for the ability of amino acid polymers to fold into three-dimentional structures is: * A. the inability of non polar groups to interact with water B. the formation of salt bridge interactions C. the hydrogen bond interactions in secondary structures D. the hydrophobicity of phenylalanine residues 13. Question Name: chapter4-26 Type: MC Objective: exam2 Item Bank: Marcos_Biochem_08_exam2 Which statement best characterizes the comparison of the oxygen binding curves of Hemoglobin and Myoglobin? A. Hemoglobin saturates at a lower partial pressure of oxygen than myoglobin. B. The myoglobin O2 binding curve is sigmoidal while the Hb O2 binding curve is hyperbolic. * C. At a fixed partial preassure of oxygen myoglobin has a higher percent saturation than hemoglobin D. All of the statements are true. Correct Answer: C

5 14. In tertiary protein structures, groups are generally are buried, while groups are in general exposed to the aqueous medium. A. Polar, nonpolar * B. Hydrophobic, polar C. ionized, nonpolar D. Charged and polar, uncharged and polar. E. Negatively ionized, positively ionized Correct Answer: B 15. Question Name: chapter4-30 Type: MC Objective: exam2 Item Bank: Marcos_Biochem_08_exam2 What statement best characterizes the structural characteristics that contribute to the functional differences between myoglobin and hemoglobin? A. Both hemoglobin and myoglobin contain alpha helices B. The Heme group lies on the surface of myoglobin while hemoglobin binds the heme group in a hydrophobic pocket. C. Myoglobin contains Fe 2+ while hemoglobin contains Fe3+. * D. Myoglobin is monomeric while hemoglobin is a tetramer 16. Which of the amino acids given below has an R-group that would increase most the flexibility of a polypeptide backbone? * A. Glycine B. Phenylalanine C. Methionine D. Isoleucine E. Proline

6 17. What is the net charge of the peeptide given below at ph=6.0? Use the following pka values: side chain (imidazole group) of Histidine (6.0); side chain (guanidino group) of Arginine (9.0); side chain (amino group) of Lysine (9.0); side chain (phenoxy) of Tyrosine (9.21); for the NH2 group (pk=11.0) and the carboxyl group (pk=2.3). Histidine-Arginine-Lysine-Histidine-Alanine-Asparagine * A. +3 B. +2 C. +1 D. 0 E. +4 This questions was fully canceled 18. Which amino acid side chain is not chiral? A. Cysteine * B. Glycine C. Proline D. Isoleucine E. All 20 natural amino acids are chiral Correct Answer: B 19. Integral membrane proteins interact on their surface with the fatty acid portions of phospholipids found in membranes. In this special case what type of amino acis would you most likely find on the surface of integral membrane proteins? A. Arginine * B. Phenylalanine C. Histidine D. Serine E. All of the residues listed are can be found on the surface of integral membrane proteins Correct Answer: B

7 20. At what ph is the side chain of histidine fully ionized? [pka of Histidine side chain (imidazole) is 6.0] * A. 2.0 B. 6.5 C. 6.0 D. 7.0 E Which pair(s) of amino acid side chains can form ionic interactions a physiological ph? A. Histidine - Glutamine * B. Aspartic acid - Lysine C. Glutamine - Arginine D. All of the pairs listed can form ionic interactions Correct Answer: B 22. Which amino acid does NOT have a cyclic structure? A. Histidine B. Tryptophan C. Phenylalanine D. Proline * E. Threonine Correct Answer: E 23. Which amino acids side chain has a full negative charge when ionized at ph 7.0? A. Cysteine B. Serine C. Tyrosine * D. Glutamic acid E. Histidine

8 24. What statement is TRUE regarding hydrongen bond between water and a protein? A. The hydrogen ion on the water molecule forms an ionic bond with a hydride ion on the biomolecule B. A hydrogen on the water molecule forms a covalent bond with a electronegative atom in the biomolecule * C. The hydrogen bond will tipically form between an oxygen atom of water and either a nitrogen, sulfur or oxygen atom of a biomolecule that has a hydrogen to donate D. The partial charge on the hydrogen atom of the water molecule interacts with the partial charge on the hydrogen atom of the biomolecule Correct Answer: C 25. What is TRUE regarding a peptide bond? A. It is partially an imino group B. It has partial double bond characteristics C. It is polar D. It can be a donor and acceptor in Hydrogen bonding * E. all of the statements listed are true Correct Answer: E 26. Which sequence listed below would most likely be found in a strand of a beta sheet which has a polar and a non-polar face? * A. Glutamic acid--isoleucine--arginine--valine--serine--alanine B. Glutamic acid-arginine--serine--threonine--histidine--threonine C. Aspartic acid-isoleucine--valine--valine-leucine--threonine D. Isoleucine--Valine-Leucine--Leucine--Valine-Valine 27. What factor(s) contribute to the stability of a protein? A. Disulfide bonds B. Hydrogen bonding C. Hydrophobicity * D. All of the factors listed contribute to protein stability

9 28. In a protein, the most conformationally restricted amino acid is ; the least conformationally restricted is. A. Methionine, Cysteine B. Isoleucine, Alanine * C. Proline, Glycine D. Alanine, Proline E. Tryptophan, Glycine Correct Answer: C 29. Select a statement that best describes the importance of disulfide bonds in protein structure. * A. Important in stabilizing extracellular proteins B. They denature proteins by increasing the solubility of nonpolar groups in water C. They are electrostatic interactions that usually occur on the surface of proteins D. They interfere with the hydrophobic properties that are responsible for a protein's native structure 30. The structural difference between Phenylalanine and Tyrosine is the same as that between what two amino acids, listed below? * A. Alanine and Serine B. Valine and Threonine C. Alanine and Cysteine D. Valine and Serine 31. Please refer to panel D. Among the curves in the graph which one would you choose to represent the curve with the highest Increase in blood CO2. A. Curve 1 B. Curve 2 C. Curve 3 * D. Curve 4

10 32. Please refer to panel D. Which of the curves in the graph would you choose to represent the highest decrease in blood ph. A. Curve 1 *B. Curve 2 C. Curve 3 D. Curve Please refer to panel D. Which of the curves would you choose to represent the behavior of Irreversibly dissociated Hb subunits. * A. Curve 1 B. Curve 2 C. Curve 3 * D. Curve Please refer to panel D. Which of the curves shown would you choose to represent a mutant form of Hemoglobin that stabilizes the R state. A. Curve 1 * B. Curve 2 C. Curve 3 D. Curve 4 Correct Answer: B

11 35. In sickle cell anemia, the structural basis for the disruption of the normal function of hemoglobin is a result of what structural feature? * A. A mutation of a single amino acid on the surface of hemoglobin leading to the formation of fibers. B. A mutation of a single amino acid residue on the core of the protein structure of hemoglobin structure, glutamate to valine. C. Disruption of the porphyrin D. Reduced affinity for oxygen E. Change in iron oxidation from Fe+2 to Fe+3. I gave the points for this question to the class those that got it right received extra points 36. Please refer to panel D. Which of the curves in the graph would you choose to represent the highest Increase in BPG concentration. A. Curve 1 B. Curve 2 C. Curve 3 * D. Curve Match the items in the alphabetic list to the numbered items. Match the pair of amino acids with most similar properties. Do not use a choice more than once A. Arginine B. Valine C. Tryptophan D. serine 37. Phenylalanine 38. Tyrosine 39. Histidine 40. Alanine Correct Answer: 37:C 38:D 39:A 40:B

12 41. What level of structural organization can better distinguish the differences between hemoglobin and myoglobin? A. Primary structure B. Secondary structure C. Tertiary structure * D. Quartenary structure E. Both structures share similarity at all levels of structural organization 42. Which structural feature, listed below, plays a key role in the allosteric properties of Hemoglobin? A. The globin fold B. The oxidation state of iron Fe+2 * C. The histidine residue that directly coordinates the heme iron D. The distal histidine Correct Answer: C

13 PANEL A Amino Acid α-carboxylic acid α-amino Side chain Alanine Arginine Asparagine Aspartic Acid Cysteine Glutamic Acid Glutamine Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tryptophan Tyrosine Valine

14 PANEL B

15 Panel C

16 PANEL D Several oxygen dissociation curves are shown in the following figure below. in the graph given below assume that curve 3 corresponds to hemoglobin in a solution containing physiological concentrations of CO 2 and BPG at a ph of 7.0. FOR QUESTIONS referring to this panel indicate which of the curves reflects the changes noted in physiological conditions by selecting a letter that corresponds to the curve # according to the following choices: Curve 1 Curve 2 Curve 3 Curve 4 You can use one curve more than once.