Dental Biochemistry Exam The total number of unique tripeptides that can be produced using all of the common 20 amino acids is

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1 Exam Questions for Dental Biochemistry Monday August 27, 2007 E.J. Miller 1. The compound shown below is CH 3 -CH 2 OH A. acetoacetate B. acetic acid C. acetaldehyde D. produced by reduction of acetaldehyde E. an example of an ether. Dental Biochemistry Exam 1 2. The total number of unique tripeptides that can be produced using all of the common 20 amino acids is A. 10,000 B. 8,000 C. 22,000 D. 1,200 E. 40, A hydrophobe is best exemplified by A. polyphosphate compounds B. a molecule such as methanol C. a saturated hydrocarbon D. the amino acid arginine 4. The role of phosphorus in biological systems involves A. development and maintenance of the skeletal system B. energy conservation and utilization C. buffering capacity D. control of protein conformation E. all of the above 5. The concept of decreased morbidity involves A. delaying age-related disabilities until the last weeks of life B. achieving immortality C. developing off-the-shelf replacements for all organs D. arresting ageing phenomena E. eliminating all disease states

2 6. If you know the standard free energy yield of a reaction, you may calculate A. the number of intermediates encountered between reactants and products B. the rate of the reaction C. the entropy of the reaction D. the equilibrium constant for the reaction 7. In the case of coupled biochemical reactions, the free energy output of the combined reactions is A. the sum of the equilibrium constants of the individual reactions B. impossible to determine C. the sum of the free energy yields for the individual reactions D. equal to that of the more favorable reaction 8. If the amino acid asparagine is titrated with a strong base, beginning at ph=1.0, there will be multiple zones of buffering. How many? A. 1 B. 2 C. 3 D. 4 E A buffer system is described by all but one of the following statements. Choose the incorrect statement. A. a buffer system is composed of an acid and its conjugate base B. a buffer system is most effective in the ph domain near the pk of its conjugate acid. C. a buffer system requires a strong acid which completely dissociates in aqueous solutions. D. a buffer system must have components in sufficient quantity to compensate for expected levels of agents which may change ph. E. the bicarbonate buffer system facilitates ph regulation of the circulation.

3 10. Which one of the following amino acids has two chiral centers? A. glycine B. valine C. serine D. alanine E. threonine 11. The only amino acid which has an achiral α-carbon is A. A B. P C. G D. C E. D 12. The important neuroacitve agent, γ aminobutyric acid, is a decarboxylation derivative of A. arginine B. hisidine C. valine D. asparagine E. glutamic acid 13. Which statement is false? A. 4-hydroxyproline is an imino acid found in collagen B. 5-hydroxylysine allows collagen to form stable cross links C. histamine is decarboxylated histidine D. tryptophan is the metabolic precursor of nitric oxide E. γ-carboxyglutamic acid is involved in blood clotting 14. The amino acids, L-leucine and L-isoleucine, are A. enantiomers B. diastereoisomers C. structural isomers D. polar amino acids E. products of posttranslational modifications of proteins

4 15. The following are characteristics of a peptide bond except A. the C-N bond is shorter than an ordinary C-N bond B. it is rigid and planar C. it exists largely in the cis conformation D. it has some polarity E. it has characteristics of a resonance system 16. Examples of 2 0 structure of proteins include all of the following except A. alpha helix B. beta pleated sheet C. polyproline helix D. the porphyrin ring of hemoglobin E. β-turn 17. In a typical globular protein, the side chains of which of the following groups of amino acids will be most likely to be present on the exterior surface? A. Leu, val, ile B. Arg, ala, leu C. Leu, gln, phe D. Cys, met, gly E. Ser, glu, lys 18. All of the following are common to fibrous proteins with the exception of A. Low solubility in aqueous solvents B. Readily hydrolyzed by digestive enzymes C. A high tensile strength D. Lengthy segments of secondary structure (helices) E. Widespread distribution in vertebrate organisms 19. The physiological buffering capacity of a protein may be ascribed to its content of A. proline B. arginine C. serine D. histidine E. aspartic acid

5 20. The sequence: Lys - Lys - Lys - Lys Lys, at ph 7.4, would A. have an overall charge of +5 B. stabilize an α-helix C. frequently be found in a β-turn D. be cleaved by the a reagent such as cyanogen bromide (CNBr) 21. Which of the following peptides woud be expected to elute last from a cation exchange chromatograhpy column operated at ph 7.0? A. Gly-Phe-Ala B. Glu-Asp-Gly C. Gly-Gly-Gly D. Lys-Met-Glu E. Lys-Ala-Arg 22. Which of the sequences in Question #21 above is likely to be cleaved with the proteolytic enzyme, chymotrypsin? 23. The hydrophobic effect A. causes the denaturation of proteins B. is responsible for the ionization of amino acids C. reduces hydrogen bonding in water D. stabilizes the native structure of globular proteins E. is another name for the process leading to prolyl hydroxylation 24. A peptide bond is A. a hydrocarbon B. a keto group C. an alcohol D. a hydrogen bond donor E. all of the above

6 25. The quaternary structure of hemoglobin A. is not important for the functioning of the protein B. is rigid and not affected by oxygen binding C. is maintained by hydrophobic bonds, salt bridges, and hydrogen bonds D. is stabilized by disulfide bonds E. accommodates six identical subunits per molecule 26. The structure of myoglobin as determined by x-ray diffraction exhibits all of the following except A. a heme group tucked into a cleft on the surface of the molecule B. an alpha helical content virtually identical to that of hemoglobin subunits C. a tertiary structure very similar to that of hemoglobin subunits D. an absence of water in the interior of the protein E. an iron atom coordinated by a tyrosine residue in the F helix 27. When separating polypeptide chains on the basis of molecular weight, one would generally use a procedure called A. Edman degradation B. magnetic resonance imaging C. reverse phase chromatography D. affinity chromatography E. size exclusion chromatography 28. Of the proteins listed below, choose the one which is a globular protein. A. keratin B. collagen C. silk D. elastin E. myoglobin 29. At physiological conditions and O 2 partial pressure of 26 torr A. the fractional saturation of myoglobin and hemoglobin is about equal B. oxygen would spontaneously pass from hemoglobin to myoglobin C. fetal hemoglobin would have a lower level of saturation than adult hemoglobin D. adult hemoglobin would be about 10% saturated with oxygen

7 30. A reagent expected to denature proteins by disrupting H-bonds is A. mercaptoethanol B. urea C. iodoacetamide D. cyanogen bromide E. ninhydrin 31. The chemical basis for the low degree of stability attained by most proteins is A. the exergonic nature of the reactions involved in protein synthesis B. the large decrease in free energy associated with protein folding C. their susceptibility to proteolysis by collagenases D. the use of chaperone molecules during synthesis E. the very modest decrease in free energy attained per residue when proteins fold 32. The major forces causing polypeptide chain to lose rotational freedom and assume a native globular conformation are A. electrostatic interactions B. entropic C. covalent bond formation D. ion binding E. addition of sequences at C-terminal end of proteins 33. Cells have proteins devoted to facilitating the folding of proteins. Which of the following agents is not involved in that type of activity? A. protein disulfide isomerase B. peptidyl prolyl isomerase C. peptidyl prolyl hydroxylase D. elastase E. heat shock proteins of the HSP 70 family

8 Key: 1. D 2. B 3. C 4. E 5. A 6. D 7. C 8. B 9. C 10. E 11. C 12. E 13. D 14. C 15. C 16. D 17. E 18. B 19. D 20. A 21. E 22. A 23. D 24. D 25. C 26. E 27. E 28. E 29. B 30. B 31. E 32. B 33. D