Culmination Practice Quiz

54 Questions | Total Attempts: 122

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Culmination Practice Quiz

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Questions and Answers
  • 1. 
    A 27-year-old intravenous drug user who shared needles with others for several years experiences flu-like symptoms with fever, malaise and muscle aches. The patient also suffers from anorexia, diarrhea and severe weight loss. Physical examination revealed generalized lymph node enlargement and laboratory tests were positive for the human immunodeficiency virus (HIV). Your diagnosis indicates that this patient suffers from acute immunodeficiency syndrome (AIDS) and you prescribe therapy with the nucleoside analog dideoxycytidine (ddC). All of the following statements regarding ddC are true, EXCEPT:
    • A. 

      Dideoxycytidine tri-phosphate cannot be incorporated into growing DNA chains.

    • B. 

      Dideoxycytidine is an analog of the nucleoside deoxycytidine.

    • C. 

      Dideoxycytidine tri-phosphate is used to terminate DNA chain elongation during DNA sequencing.

    • D. 

      Dideoxycytidine has hydrogen groups on the 2’- and 3’-carbons of deoxyribose.

    • E. 

      Dideoxycytidine is converted to a nucleoside tri-phosphate by cellular kinases.

  • 2. 
    A strain of E. coli is unable to induce the operons encoding the genes responsible for the metabolism of several sugars that can normally act as carbon sources when glucose is unavailable. The most likely explanation is a mutation that...
    • A. 

      Alters the specificity of the sigma factor of RNA polymerase.

    • B. 

      Prevents the binding of RNA polymerase to promoters.

    • C. 

      Increases the affinity of CAP for cAMP.

    • D. 

      Decreases the affinity of CAP for cAMP.

    • E. 

      Causes CAP to bind constitutively to CAP-binding sites.

  • 3. 
    What two organelles are shown in the micrograph?
    • A. 

      Peroxisomes, Rough Endoplasmic Reticulum

    • B. 

      Lipid Droplets, Smooth Endoplasmic Reticulum

    • C. 

      Mitochondrion, Smooth Endoplasmic Reticulum

    • D. 

      Lysosomes, Golgi Apparatus

  • 4. 
    Biochemical mechanisms for regulating enzyme activity include ALL of the following EXCEPT which ONE:
    • A. 

      Allosteric interactions

    • B. 

      Phosphorylation of amino acid side chains

    • C. 

      Proteolytic cleavage of peptide bonds within the zymogen

    • D. 

      Degradation of the enzyme

    • E. 

      Converting activated enzymes to zymogens

  • 5. 
    Match each of the statements with one or more of the structures shown below. Which statement CANNOT be matched with a structure?
    • A. 

      This amino acid residue can form disulfide bonds under oxidizing conditions.

    • B. 

      This residue can adopt a cis conformation of the peptide bond within a protein.

    • C. 

      The side chain of this amino acid has multiple atoms that can participate in hydrogen bonds.

    • D. 

      The side chain of this amino acid is positively charged at physiologic pH.

    • E. 

      This amino acid can serve as an attachment site for O-linked polysaccharides (sugars) in glycoproteins.

  • 6. 
    Which ONE of the following best explains the side effects of ALLI (ORLISTAT), including fatty stools, diarrhea, and flatulence?
    • A. 

      Failure to inhibit gastric lipase

    • B. 

      Excess undigested fats

    • C. 

      Accumulation of Orlistat in the intestinal tract

    • D. 

      Liver damage

    • E. 

      Non-specific inhibition of many enzymes

  • 7. 
    One of our cases of the week is a 32 year old male college graduate who works full time. He is 68” inches tall and weighs 154 pounds. His blood pressure is 135/82 and his glycated hemoglobin (a1C) is 6.2%. Which of the following statements is false?
    • A. 

      His blood pressure of 135/82 identifies him as risk for hypertension

    • B. 

      His BMI places him in the “normal” range

    • C. 

      We should repeat the a1C and order a fasting plasma glucose (FPG) test on a non-urgent basis

    • D. 

      His blood pressure is within the “normal” range

    • E. 

      His hemoglobin a1C level of 6.2% identifies him as at increased risk of diabetes

  • 8. 
    Hemoglobin is an allosteric protein. This means that an interaction at one site has an effect at a spatially distinct site in the protein. Which ONE of the following statements about allosteric effects of hemoglobin is CORRECT?
    • A. 

      Nitric oxide (NO) is released from Hb preferentially at sites of active metabolism, because a cysteine has a much higher affinity for NO in oxyhemoglobin than in deoxyHb.

    • B. 

      Hemoglobin and myoglobin molecules can bind 2,3-bisphosphoglycerate, which decreases their affinity for oxygen.

    • C. 

      Carbon dioxide increases the affinity of hemoglobin for oxygen both by binding to the N-terminus and through the Bohr effect.

    • D. 

      The Hill Coefficient of hemoglobin indicates that hemoglobin tetramers have no more than three oxygen molecules bound.

    • E. 

      Sites of active metabolism have higher concentration of carbonic acid, which shifts the hemoglobin oxygen dissociation curve to the left.

  • 9. 
    A 40 year old woman and her two children went to the doctor with complaints of headaches, nausea, weakness and dizziness. At first, the physician thinks that the family is suffering from the flu. However, after hearing about the new wood-burning stove installed in their house this past winter, the physician suspected carbon monoxide poisoning. To treat them for carbon monoxide poisoning, the physician…
    • A. 

      Gave them hydroxyurea to increase the synthesis of HbF.

    • B. 

      Had them ingest a reducing agent to regenerate the oxygen binding form of Hb.

    • C. 

      Gave them hydroxyurea to increase the synthesis of HbF.

    • D. 

      Administered air with a higher percent of carbon dioxide than is normal, to compete with the carbon monoxide.

    • E. 

      Administered 100% oxygen to displace the competitive inhibitor.

  • 10. 
    “Stripped” hemoglobin is Hb obtained from RBCs that have been lysed (broken open) and dialyzed to remove any small molecules such as organic phosphates. The oxygen saturation curves for Hb from whole blood and for stripped Hb are shown below. Which ONE of the following statements related to these curves is CORRECT?
    • A. 

      In going from a pO2 of 20mmHg to a pO2 of 100mmHg, stripped Hb takes up about three times as much oxygen as does Hb from whole blood, per mole of tetramer.

    • B. 

      In going from a pO2 of 100mmHg to a pO2 of 20mmHg, Hb from whole blood releases about three times as much oxygen as does stripped Hb, per mole of tetramer.

    • C. 

      The P50 value for stripped Hb is ~ 40mmHg lower than that for whole blood.

    • D. 

      The P50 value for stripped Hb is ~ 15mmHg higher than that for whole blood.

    • E. 

      Changing the pH would not affect the oxygen saturation curve of the stripped Hb.

  • 11. 
    Which ONE of the following statements concerning nitric oxide is CORRECT? The delivery of nitric oxide by hemoglobin....
    • A. 

      Depends on the differing reactivity of the R and T forms of Hb

    • B. 

      Leads to decreased blood flow at tissue sites with low oxygen pressure.

    • C. 

      Can competitively inhibit cyanide poisoning.

    • D. 

      Competes with carbon dioxide binding.

    • E. 

      Is mediated by formation of C?-CH2-S-NO bond with Met.

  • 12. 
    You are studying a biochemical pathway that requires ATP as an energy source. To your dismay, the reactions soon stop, partly because the ATP is rapidly used up and partly because an excess of ADP builds up and inhibits the enzymes involved. You are about to give up when the following table from a biochemistry textbook catches your eye.
    • A. 

      Pyrophosphate

    • B. 

      Glucose 6-phosphate and enzyme E

    • C. 

      Creatine phosphate and enzyme A

    • D. 

      A vast excess of ATP

    • E. 

      Pyrophosphate and enzyme D

  • 13. 
    A common means of providing energy to an energetically unfavorable reaction in a cell is by…
    • A. 

      Coupling of the synthesis of ATP to the reaction.

    • B. 

      Enzyme catalysis of the reaction.

    • C. 

      Generation of a higher temperature by the cell.

    • D. 

      Coupling of ATP hydrolysis to the reaction.

    • E. 

      Transfer of a phosphate group from the substrate to ADP.

  • 14. 
    Which of the following reactions are energetically favorable?
    • A. 

      Base + sugar + phosphate --> nucleotide

    • B. 

      N2 + H2 --> ammonia

    • C. 

      Sucrose --> CO2 + H2O

    • D. 

      CO2 + H2O --> sugar

    • E. 

      Amino acid + amino acid --> peptide

  • 15. 
    A comatose laboratory technician is rushed into the emergency room. A symptom you observe is that her body is unusually warm to the touch, indicating an extremely high fever. She dies while you are examining her. You later learn that her lab has been working on metabolic inhibitors and that there is a high likelihood that she ingested, by accident, an extremely high dose of one of them. The most likely compound is….
    • A. 

      2,4-dinitrophenol

    • B. 

      Atractyloside

    • C. 

      Rotenone

    • D. 

      Oligomycin.

    • E. 

      Cyanide

  • 16. 
    When Peter Mitchell first proposed the chemiosmotic mechanism for oxidative phosphorylation, it was not taken seriously. Slowly, evidence accumulated to support it. Key pieces of evidence that support the chemiosmotic mechanism include all of the following EXCEPT:
    • A. 

      Disruption of the inner mitochondrial membrane stops ATP formation.

    • B. 

      Complex I can only react with NADH from the matrix side while complex III can only reduce cytochrome c from the intermembrane space.

    • C. 

      A pH gradient is set up across the inner mitochondrial membrane, with the pH higher in the matrix.

    • D. 

      At least one component of each major electron transport complex is coded for by mt DNA.

    • E. 

      Oxidation-reduction reactions of the electron transport chain generate a gradient of protons across the inner mitochondrial membrane.

  • 17. 
    A defect in the adenine nucleotide carrier (also known as adenine nucleotide translocase) would lead to which of the following?
    • A. 

      A decrease in the cytosolic concentration of ADP.

    • B. 

      A decrease in the activity of mitochondrial outer membrane transport proteins.

    • C. 

      An increase in mitochondrial AMP.

    • D. 

      An increase in mitochondrial ATP production.

    • E. 

      A decrease in the cytosolic concentration of ATP.

  • 18. 
    Complete the following sentence so that it is CORRECT: “Complete oxidation of one acetyl CoA leads to...”
    • A. 

      The reduction of one NAD+.

    • B. 

      The net consumption of one oxaloacetate.

    • C. 

      The net synthesis of one citrate.

    • D. 

      The production of six ATPs.

    • E. 

      The release of two CO2.

  • 19. 
    In addition to the proteins of the pyruvate dehydrogenase complex, the conversion of pyruvate to acetyl CoA also requires which ONE of the following combinations of co-factors:
    • A. 

      CoA, lipoic acid, biotin and ATP

    • B. 

      CoA, ATP, NAD+ and riboflavin

    • C. 

      CoA, thiamine pyrophosphate and folic acid

    • D. 

      CoA, lipoic acid, thiamine pyrophosphate and FAD

  • 20. 
    Many factors contribute to studying causation; the definition of “a cause” is….
    • A. 

      An event or exposure that occurs more often in people with a disease than without

    • B. 

      An event, condition, or characteristic that plays an important role in disease occurrence..

    • C. 

      An event that precedes the onset of a disease

    • D. 

      A hazard or exposure that occurs in workplaces where people get sick.

    • E. 

      All of the above

  • 21. 
    DNA gyrase is a prokaryotic DNA topoisomerase II. Which ONE of the following DNA conformations shown on the left will be converted to the conformation shown on the right upon treatment with DNA gyrase?A) B) C) D)
    • A. 

      A

    • B. 

      B

    • C. 

      C

    • D. 

      D

  • 22. 
    A middle-aged man shows symptoms characteristic of tuberculosis, a disease condition caused by the bacterium Mycobacterium tuberculosis. Laboratory analysis of a sputum specimen revealed that in addition to the wild-type Mycobacterium tuberculosis bacterium, a variant strain was also present that showed a conditional mutation affecting the 5’ to 3’ exonuclease activity of DNA polymerase I. Which ONE of the following phenotypes is the most obvious defect associated with a conditional mutation affecting the 5’ to 3’ exonuclease activity of DNA polymerase I under conditions where it is INACTIVE?
    • A. 

      The bacterial genome shows a defect in lagging strand DNA chain elongation.

    • B. 

      The bacterial genome shows a defect in mismatch repair.

    • C. 

      The bacterial genome shows accumulation of telomeric repeats.

    • D. 

      The bacterial genome shows a defect in the removal of RNA primers.

    • E. 

      The bacterial genome shows an increased number of replication errors.

  • 23. 
    All of the following statements are true about transposition, EXCEPT:
    • A. 

      Transposons may either activate or inactivate a gene.

    • B. 

      In transposition, both the donor and target sites must be homologous.

    • C. 

      Integration of human immunodeficiency virus (HIV) in the human genome occurs via a “transposition-like” mechanism.

    • D. 

      Transposons have “insertion sequences” that are recognized by transposase.

    • E. 

      Transposons can move from one location to a different one within a chromosome.

  • 24. 
    Dynein, kinesin and myosin are molecular motors. Select the incorrect statement:
    • A. 

      Kinesins and dynein can move on the same structure.

    • B. 

      The “power stroke” occurs when the products of hydrolysis are released.

    • C. 

      All three classes of motors are ATPases.

    • D. 

      Dynein moves on microtubules towards the centrosome.

  • 25. 
    The role of ATP hydrolysis in actin polymerization is similar to the role of GTP hydrolysis in tubulin polymerization (N=nucleotide). Which statement is incorrect?
    • A. 

      When the subunit at the + end of the polymer is NTP, the end is more stable than if the nucleotide is NDP.

    • B. 

      The energy of NTP hydrolysis is required for polymerization.

    • C. 

      The nucleotide in the subunit at the end of the polymer affects the equilibrium constant of subunit addition at the end.

    • D. 

      NTP hydrolysis occurs after polymerization.

  • 26. 
    Foot and mouth disease virus infection results in dramatic host translation shut-down. This is primarily due to the inactivation of which host factor?
    • A. 

      EIF4E

    • B. 

      EIF1A

    • C. 

      EIF4G

    • D. 

      EEF1A

    • E. 

      Poly(A) binding protein

  • 27. 
    Which class of antibiotics can be used to suppress the formation of truncated protein resulting from genetically encoded premature stop codons?
    • A. 

      Peptioglycan inhibitors

    • B. 

      Aminoglycosides

    • C. 

      RNA polymerase inhibitors

    • D. 

      Tetracyclines

    • E. 

      Lincosamides

  • 28. 
    Initiation of mRNA transcription in a eukaryote...
    • A. 

      Unlike bacterial genes, does not require specific DNA sequences.

    • B. 

      Requires canonical -10 and -35 sequences.

    • C. 

      Requires sequence specific binding by RNA polymerase II.

    • D. 

      Is not a regulated step for determining the level of gene expression.

    • E. 

      Requires general transcription factors that position RNA polymerase at the transcriptional start site.

  • 29. 
    Which of the following statements about transcription factors is not true?
    • A. 

      Transcription factors promote disassembly of RNA Pol II to terminate transcription.

    • B. 

      Several transcription factors may be involved in regulating the expression of a single gene.

    • C. 

      General transcription factors are required for transcription of most, and probably all, genes.

    • D. 

      Transcription factors often bind to specific DNA sequences.

    • E. 

      Transcription factors can bind close to or even thousands of base pairs away from the promoter of genes they regulate.

  • 30. 
    The glucocorticoid receptor is an example of the “receptor as a transcription factor” pathway of signal transduction. If a mutation occurred in the gene encoding the glucocorticoid receptor, such that the receptor protein no longer could bind zinc atoms, which activity would be most directly affected?
    • A. 

      Ligand (hormone) binding

    • B. 

      Transcriptional activation

    • C. 

      DNA binding

    • D. 

      Nuclear localization

    • E. 

      Targeting of the receptor protein to the plasma membrane

  • 31. 
    • A. 

      Knowledge of drug atoms that do not interact with the protein is as useful in drug design as knowledge of drug atoms that contact the protein.

    • B. 

      Because proteins interact with drugs like "locks and keys" knowledge of a protein's structure allows direct design of high-affinity drugs.

    • C. 

      Most drug leads in structure assisted drug development projects are initially identified by screens of large libraries of synthetic or natural compounds in biochemical or cell-based assays.

    • D. 

      Computational modeling, chemical synthesis, activity assays, and structure determination are steps that are all repeated multiple times during structure assisted drug development.

    • E. 

      X-ray crystallography is the most commonly used method for determining atomic-resolution structures of protein-drug complexes.

  • 32. 
    What is the three letter code for the hexapeptide shown below in one letter code? P-A-L-E-T-N
    • A. 

      Pro-Ala-Leu-Glu-Thr-Asn

    • B. 

      Pro-Ala-Leu-Asp-Tyr-Asn

    • C. 

      Pro-Ala-Leu-Glu-Tyr-Gln

    • D. 

      Phe-Ala-Leu-Asp-Thr-Gln

    • E. 

      Phe-Ala-Leu-Asp-Tyr-Asn

  • 33. 
    • A. 

      Proteolysis followed by paper electrophoresis

    • B. 

      Acid hydrolysis followed by amino acid analysis

    • C. 

      Immunoblot (Western) analysis

    • D. 

      Nuclear magnetic resonance (NMR) analysis

    • E. 

      N-terminal amino acid sequence (Edman) analysis

  • 34. 
    Protein tyrosine kinases are signal transduction proteins that phosphorylate themselves and other protein substrates at specific tyrosine residues. Inhibitors of protein tyrosine kinases are currently being pursued as promising therapeutics for the treatment of specific cancers. (In particular, the Novartis drug Gleevek, an inhibitor of the Abl kinase made headline news this past summer.) Consider a hypothetical new kinase inhibitor, a derivative of the amino acid tyrosine, with the indicated structure. It is shown in its fully protonated form with the two dissociable protons shown in bold and underlined. Bio-availability will depend on the charged state of this compound, so a titration is performed to determine important parameters such as pKa and pI values. The titration of 1 mole of this compound starting from the fully deprotonated form is shown. Use your knowledge of the pKa values of similar groups in tyrosine to interpret the titration. Which ONE of the following statements is CORRECT?  
    • A. 

      The isoelectric point is 6.5

    • B. 

      A region of maximum buffering occurs at "B".

    • C. 

      The isoelectric form occurs at "C".

    • D. 

      The pKa of the hydroxyl group substituent of the aromatic ring is 6.5.

    • E. 

      At pH 10.0, the most abundant species has a net charge of –1.

  • 35. 
    Cimetidine (Tagamet) is a histamine H2-receptor antagonist that is widely used in the treatment of heartburn and peptic ulcers. It is absorbed in the gastrointestinal tract by passive diffusion across a lipid bilayer. Uncharged molecules diffuse readily across membranes while charged molecules do not. Consider a total concentration of 0.1 mg/ml cimetidine in each of the above gastrointestinal locations. Which ONE of the following statements is INCORRECT?  
    • A. 

      In the small intestine, the concentration of neutral cimetidine is greater than the concentration of protonated cimetidine.

    • B. 

      The concentration of protonated cimetidine is approximately the same in both fed and fasted stomachs.

    • C. 

      The concentration of neutral cimetidine is approximately 100 times greater in the small intestine than in the duodenum.

    • D. 

      In the duodenum, the concentration of neutral cimetidine is 10 times less than the concentration of protonated cimetidine.

    • E. 

      In the fasted stomach, the concentration of neutral cimetidine is approximately 0.1 ng/ml.

  • 36. 
    The disulfide bond-containing peptide shown below is digested with trypsin, a protease that cleaves peptide bonds on the C-terminal side of Lys and Arg residues. The resulting peptides are then separated by paper electrophoresis at pH 7.0. The peptide that migrates furthest towards the cathode (negative electrode) is isolated and amino acid analysis is performed. Amino acid analysis, which involves incubating the peptide in 12 M hydrochloric acid at elevated temperatures, hydrolyzes all peptide bonds, generating individual amino acids that can be separated and identified by chromatography. What is the amino acid composition of this peptide?
    • A. 

      Asp, Leu, Lys, Thr

    • B. 

      Ala, Leu, Lys, Thr

    • C. 

      Ala, Cys, Leu, Lys, Thr

    • D. 

      Ala, Arg, Leu, Lys, Thr

    • E. 

      Ala, Asp, Arg, Cys, Glu, Gly, Leu, Lys, Thr

  • 37. 
    Examine reactions from 1 to 5 as shown above and pick out the ONE INCORRECT statement:
    • A. 

      The enzyme catalyzing reaction (4) is a isomerase

    • B. 

      The enzyme catalyzing reaction (2) is a hydrolase

    • C. 

      The enzyme catalyzing reaction (1) is an oxido-reductase

    • D. 

      The enzyme catalyzing reaction (5) is a synthetase

    • E. 

      The enzyme catalyzing reaction (3) is a lyase

  • 38. 
    When the substrate concentration is 4Km, the ratio of v/Vmax is…..
    • A. 

      0.25

    • B. 

      1.25

    • C. 

      5

    • D. 

      0.8

    • E. 

      1

  • 39. 
    Four mammalian isozymes of hexokinase are known (Types I - IV), with the Type IV hepatic isozyme referred to as glucokinase. As isozymes, the four hexokinases have the following common property:
    • A. 

      PH optimum

    • B. 

      Equilibrium constant for the reaction

    • C. 

      Temperature optimum

    • D. 

      Kinetics of heat inactivation

    • E. 

      Vmax values

  • 40. 
    The enzyme aspartate transcarbamylase condenses carbamoyl phosphate and aspartate to form N-carbamoyl aspartate with positive cooperativity. ATP is an allosteric activator of the enzyme. Which ONE of the [S] (substrate) dependence curves (A --> E) describes the effect of added ATP on the velocity of the reaction?A) B) C) D) E)
    • A. 

      A

    • B. 

      B

    • C. 

      C

    • D. 

      D

    • E. 

      E

  • 41. 
    The blood of a hospital patient, X, was routinely screened by electrophoresis prior to surgery, under conditions that resolve hemoglobin, and found to contain an abnormal electrophoretic band, as shown below. Which ONE of the following can be determined about the abnormal hemoglobin from patient X?
    • A. 

      Its electrophoretic pattern is consistent with Sickle Cell Anemia.

    • B. 

      It has a higher isoelectric point than HbA.

    • C. 

      Its electrophoretic pattern is consistent with an Arg to Leu change in one beta-allele.

    • D. 

      It has a higher oxygen affinity than HbA.

    • E. 

      Its electrophoretic pattern is consistent with the compound heterozygote HbSC.

  • 42. 
    A 10 year old African American boy was admitted to the hospital because he was experiencing severe chest pain. He had been hospitalized on several previous occasions for vaso-occlusive episodes that caused him to experience severe pain that could not be managed with non-prescription pain relievers. He was slightly jaundiced, short of breath, easily tired and feverish. Following some blood tests you diagnose his condition as sickle cell anemia and recommend that the patient do all of the following EXCEPT:  
    • A. 

      Increase intake of fluids.

    • B. 

      Take medication to increase BPG levels in RBCs.

    • C. 

      Take treatments to increase HbF levels

    • D. 

      Avoid foods or situations that would lower body pH values.

    • E. 

      Avoid high altitudes.

  • 43. 
    A husband and wife both have sickle cell trait, and are expecting their first child in 7 months. They are concerned about the possibility of their child having sickle cell anemia. You explain that DNA prenatal testing for the base substitution is the appropriate diagnostic procedure. You also explain that examination of the blood of the fetus for sickling after deoxygenation will not reveal if the child will have sickle cell anemia, because:  
    • A. 

      The beta-chain with the sickle cell mutation would not be expressed in the fetus.

    • B. 

      HbA2 interferes with sickling.

    • C. 

      There is not sufficient BPG in fetal red blood cells to cause sickling.

    • D. 

      Fetal red blood cells have a higher oxygen affinity than adult ones.

    • E. 

      The pH of fetal red blood cells is higher than adult red blood cells.

  • 44. 
    K.S. is a 37-year old male who was recently diagnosed with cancer of the right colon.Careful family history reveals that he has a sister affected with endometrial cancer (age 43) and a brother diagnosed with colon cancer (age 45). His mother died of ovarian cancer at age 49. Immunohistochemical (IHC) analysis of the tumor reveals nuclear staining for MLH1 . Which protein is most likely absent from the tumor sample (as detected by IHC)?
    • A. 

      PMS2

    • B. 

      MSH2

    • C. 

      PMS1

    • D. 

      MLH3

    • E. 

      MSH3

  • 45. 
    K.T., a seven-year old girl, was referred to the neurology clinic for evaluation of severe unstable gait and poor balance. She has a past history significant for frequent ear and sinus infections and was recently diagnosed with pneumonia for the second time.On physical examination, she had prominent dilated, fine blood vessels in the conjunctiva and also a capillary rash in a butterfly distribution over the bridge of her nose. Ataxia is noted as well as absent deep tendon reflexes. To confirm the suspected diagnosis, a sample of this patient’s white blood cells are obtained, lysed and examined by western blotting. An absence of which protein is most likely. 
    • A. 

      Aprataxin

    • B. 

      XP-C

    • C. 

      K-Ras

    • D. 

      ATM kinase

    • E. 

      WRN, a REQ helicase

  • 46. 
    J.S. was born after a 34 week gestation period.In the first 24 hours of life, he developed respiratory distress. At 3 weeks he became dependent on a ventilator, which he required for the rest of his life. By 6 weeks he had developed neurologic problems. A heart murmur was observed and tests revealed a cardiomyopathy. Between 5 and 16 weeks, he developed progressive lactic acidemia, an increased ratio of lactate to pyruvate in the blood, and an elevation of serum pyruvate. The lactic acidemia persisted until the child died of cardiopulmonary arrest at 16 weeks of age. Tests performed on the infant showed normal glycolytic and gluconeogenic enzyme levels. Pyruvate dehydrogenase activity was also normal. After the infant’s death, mitochondria were prepared from his heart. The rate of oxygen consumption from these mitochondria measured with succinate as a substrate was normal. When the mitochondria were incubated with pyruvate or malate, however, the rate of oxygen consumption was extremely low. Electron paramagnetic resonance measurements EPR showed a lower than normal content of iron. Which ONE of the following would you expect to be true in this patient based on this history.
    • A. 

      The data obtained with isolated mitochondria suggest that the mitochondria were uncoupled.

    • B. 

      The most likely site of the defect is a cytochrome.

    • C. 

      The data obtained with isolated mitochondria sugest that the patient has an inability to transfer electrons from succinate to CoQ.

    • D. 

      The most likely site of the defect is an Fe-S center in complex I in the electron transport chain.

    • E. 

      The presence of lactic acidemia suggests a problem at the level of pyruvate metabolism.

  • 47. 
    Drugs that inhibit topoisomerases are used as anti-cancer agents. Complete the following sentence so that it is CORRECT: DNA topoisomerase I...
    • A. 

      Creates and reseals double-stranded breaks in double-stranded DNA.

    • B. 

      Regulates the level of superhelicity of DNA in cells

    • C. 

      Introduces negative supercoils into linear DNA molecules.

    • D. 

      Requires ATP hydrolysis to complete its reaction.

    • E. 

      Bacterial DNA gyrase is one type of DNA topoisomerase I

  • 48. 
    K.T., a seven-year old girl, was referred to the neurology clinic for evaluation of severe unstable gait and poor balance. She has a past history significant for frequent ear and sinus infections and was recently diagnosed with pneumonia for the second time.On physical examination, she had prominent dilated, fine blood vessels in the conjunctiva and also a capillary rash in a butterfly distribution over the bridge of her nose. Ataxia is noted as well as absent deep tendon reflexes.Frequent infections are characteristic of this patient’s disease. This is best explained by
    • A. 

      Loss of helicase activity which causes epithelial sloughing and plugging of the airways

    • B. 

      Increased Single Strand Breaks which make epithelial cells more susceptible to bacterial toxin

    • C. 

      Base-pair Mismatching which affects tracheal mucus production

    • D. 

      Double-Strand breaks that persist during B and T cell differentiation which lead to immunodeficiency

  • 49. 
    Which one of the statements about Brown adipose tissue BAT is INCORRECT?
    • A. 

      UCP (uncoupling protein) molecules are found in mitochondria in BAT, but not in skeletal muscle mitochondria

    • B. 

      When people are kept in a cool room, the activity of their BAT increases

    • C. 

      Shivering generates heat through BAT.

    • D. 

      BAT is a heat generating and not an energy generating tissue

    • E. 

      In people, BAT has been found to be most active in newborns but also present in adults

  • 50. 
    Referring to the Z table above, what is the appropriate interpretation of the cell denoted by the red arrow which reads 0.4505.
    • A. 

      45% of the curve lies below (to the left) of a Z value of 1.65

    • B. 

      95% of the curve lies below (to the left) of a Z value of 1.65

    • C. 

      This is the appropriate Z score for a two tailed test with alpha=.05

    • D. 

      A Z value of 1.60 corresponds to a P value of 0.45

    • E. 

      A Z value of 1.65 corresponds to a P value of 0.45

  • 51. 
    Which ONE of the following statements related to the malate-aspartate shuttle is CORRECT?
    • A. 

      The shuttle is limited by the concentration of transaminases

    • B. 

      Cytoplasmic and mitochondrial forms of malate dehydrogenase are necessary for this shuttle

    • C. 

      Another name for this is the glycerol 3-phosphate shuttle

    • D. 

      In this shuttle mechanism, either 2 or 3 ATP molecules will be generated for every NADH generated by glycolysis, depending on the conditions

    • E. 

      The shuttle only operates when the NAD+: NADH ratio is higher in the cytoplasm than in the mitochondrial matrix

  • 52. 
    Which organelle is marked by the arrows?  
    • A. 

      Peroxisomes

    • B. 

      Nucleolus

    • C. 

      Lysosomes

    • D. 

      Golgi complex

    • E. 

      Mitochondria

  • 53. 
    A domain of lactate dehydrogenase is shown as a ribbon diagram below. Secondary structural elements are labeled with letters. Which ONE of the following statements concerning this structure is TRUE?
    • A. 

      The sequence D-V-R-F-K-I would be likely to be found in a beta strand of a parallel beta sheet, such as element A.

    • B. 

      Substitution of I with D in element A would be expected to destabilize the protein by disrupting the hydrophobic core.

    • C. 

      The loop connecting beta strand C to alpha helix D is expected to be composed primarily of hydrophobic amino acid residues.

    • D. 

      Substitution of K with R on the exposed surface of element D would be expected to destabilize the protein by altering its net charge.

    • E. 

      The sequence D-V-R-F-K-I would be likely to be found in an amphipathic helix such as element D.

  • 54. 
    • A. 

      The substitution of isoleucine -> glutamate on the hydrophobic face of an alpha helix.

    • B. 

      The insertion of one additional hydrophobic amino acid into the middle of a beta strand of an anti-parallel beta sheet.

    • C. 

      The substitution of Met -> Leu in the middle of a beta strand of an anti-parallel beta sheet.

    • D. 

      The substitution of Ala -> cis-Pro within the middle of an alpha helix.

    • E. 

      The substitution of cis-Pro -> His within a turn at the surface of a protein.