Molecule 3g03 Test 3

25 Questions

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Molecule Quizzes & Trivia

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Questions and Answers
  • 1. 
    A portion of the nucleotide sequence from the DNA coding strand of the chick ovalbumin gene is shown here.      CTCAGAGTTCACCATGGGCTCCATCGGTGCAG-      CAAGCATGGAA-(149bp)-ATTCTTTGGCAGATGT-      GTTTCCCCTTAAAAAGAA What is the partial amino acid sequence of the encoded protein?
    • A. 

      MGSIGAASME-(50 a.a.)-FFGRCVSP

    • B. 

      MSGIAAGSME-(50 a.a.)-EEGRCVSP

    • C. 

      MAASMEGSIG-(50 a.a.)-FFGRCVSP

    • D. 

      MGSIGAASME-(50 a.a.)-RCVSFFGP

    • E. 

      MAASMEGSIG-(50 a.a.)-FCVSFGRP

  • 2. 
    The isoelectric point of Tyr is
    • A. 

      5.7

    • B. 

      9.83

    • C. 

      6.33

    • D. 

      5.0

    • E. 

      10.0

  • 3. 
    The isoelectric point of His-Tyr is
    • A. 

      7.68

    • B. 

      4.12

    • C. 

      5.46

    • D. 

      9.89

    • E. 

      5.7

  • 4. 
    The isoelectric point of Ala-His-Asp-Arg-Val-Gln is
    • A. 

      7.95

    • B. 

      11.17

    • C. 

      4.97

    • D. 

      7.0

    • E. 

      3.03

  • 5. 
    To make a phosphate buffer at pH 12.38 starting with one liter of 10 mM phosphoric acid (H3PO4; pKs are of 2.15, 6.82, and 12.38), you could add
    • A. 

      5 millimoles of KOH

    • B. 

      15 millimoles of KOH

    • C. 

      25 millimoles of KOH

    • D. 

      20 millimoles of KOH

    • E. 

      You can't make a buffer by adding HCL or KOH

  • 6. 
    To make an acetate buffer at pH 4.76 (pK = 4.76) starting with 250 mL of 0.2 M acetic acid (pK = 4.76), you could add:
    • A. 

      0.05 moles of HCL

    • B. 

      0.025 moles of NaOH

    • C. 

      You can't make a buffer by adding HCL or NaOH

    • D. 

      0.05 moles of NaOH

    • E. 

      0.2 moles of HCL

  • 7. 
    Given the Henderson-Hasselbalch equation as pH = pK + log {[A-] /[HA]}, what is the probability of finding the form of histidine shown in Figure 2 at pH 4 assuming the various pK's of histidine are:      pK amino = 10.0; pK carboxyl = 2.0; pK imidazole = 6.0
    • A. 

      (1/1000001)x(1/101)x(1/101)

    • B. 

      (1/100001)x(1/101)x(1/101)

    • C. 

      (1/10001)x(1/1001)x(1/1001)

    • D. 

      (1/1001)x(1/10001)x(1/10001)

    • E. 

      (1/101)x(1/100001)x(1/100001)

  • 8. 
    O2 binds to the heme group of myoglobin such that binding is _____ when the oxygen concentration is equal to the dissociation constant
    • A. 

      1/4 - maximal

    • B. 

      1/8 - maximal

    • C. 

      1/2 - maximal

    • D. 

      1/16 maximal

    • E. 

      None of the rest

  • 9. 
    The _______, which are identical in all members of a protein family, are essential for the structure and/or function of the proteins and cannot be replaced by other residues.
    • A. 

      Homologous proteins

    • B. 

      Invariant residues

    • C. 

      Variable residues

    • D. 

      Hemoglobin

    • E. 

      All of the rest

  • 10. 
    BPG binds to deoxyhemoglobin but not to oxyhemoglobin.  It therefore ______ hemoglobin's oxygen-binding affinity by stabilizing the deoxyhemoglobin conformation.
    • A. 

      Increases

    • B. 

      Reduces

    • C. 

      Improves

    • D. 

      Completely abolish

    • E. 

      None of the rest

  • 11. 
    The tubulin dimer has binding sites that bind
    • A. 

      ATP and ADP

    • B. 

      GTP and ATP

    • C. 

      GDP and ADP

    • D. 

      GTP and ADP

    • E. 

      GTP and GDP

  • 12. 
    Specificity pocket in trypsin refers to a hole on the enzyme surface at the active site that accommodates the residues on the _____ side of the _____ peptide bond
    • A. 

      C-terminal, catalytic triad

    • B. 

      C-terminal, scissile

    • C. 

      N-terminal, catalytic triad

    • D. 

      N-terminal, serine protease

    • E. 

      N-terminal, scissile

  • 13. 
    • A. 

      The fractional saturation when pO2 = 30 torr is 0.24

    • B. 

      The fractional saturation when pO2 = 100 torr is 0.59

    • C. 

      Hemoglobin can only use 25% of its capacity to deliver O2 to the tissues

    • D. 

      Hemoglobin is fully oxidized in the tissues

    • E. 

      None of the rest

  • 14. 
    Given hexacoordinate Fe(II) in heme is bright red and pentacoordinate Fe(II) is blue. Which of the following statements is correct?
    • A. 

      Oxidized hemoglobin Fe(III) is bright red

    • B. 

      Iron in oxygenated hemoglobin is pentacoordinated Fe(II)

    • C. 

      Hemoglobin in the venous blood is bluish in colour

    • D. 

      Hemoglobin in the venous blood contains hexacoordinate Fe(II)

    • E. 

      None of the rest

  • 15. 
    Which of the following statements is correct about hemoglobin?
    • A. 

      Decrease in [H+] promotes the shift of hemoglobin from the oxy to the deoxy conformation

    • B. 

      Increase in oxygen affinity improves oxygen delivery to the muscle where it is needed

    • C. 

      Hemoglobin in the blood passing through highly active muscle has less oxygen affinity

    • D. 

      Fetus hemoglobin has higher p50 than that of mother

    • E. 

      None of the rest

  • 16. 
    Lampreys are among the world's most primitive vertebrates and are therefore interesting organisms to study. It has been shown that lamprey hemoglobin forms a tetramer when deoxygenated, but when the hemoglobin becomes oxygenated, the tetramers dissociate into monomers. The binding of oxygen to lamprey hemoglobin is influenced by pH; as in human hemoglobin, the deoxygenated form is favoured when the pH decreases. Glutamate residues on the surface of the monomers play an important role. Which of the following statements is incorrect?
    • A. 

      Negatively charged glutamate side chains on the surface of the oxygenated lamprey monomer would resist association due to the charge-charge repulsion

    • B. 

      When the pH decreases, excess protons would bind to the glutamate side chains, neutralizing them

    • C. 

      When pH decreases, lamprey hemoglobins form monomer

    • D. 

      Lamprey hemoglobins exist as tetramers in metabolically active tissues

    • E. 

      Lamprey hemoglobins exist as monomers in lung tissues

  • 17. 
    Since proteins are limited in their abilities to catalyze oxidation-reduction reactions, enzymes often employ ______ to assist with catalysis.
    • A. 

      Leaving group

    • B. 

      Leaving group

    • C. 

      Coenzymes

    • D. 

      Acid

    • E. 

      Base

  • 18. 
    An uncatalyzed reaction has a rate of 4.1 x 10^-7.sec-1. When an enzyme is added the rate is 8.2 x 10^4.sec-1. Calculate the rate enhancement caused by the enzyme.
    • A. 

      3.2 x 10^4

    • B. 

      1.34 x 10^-2

    • C. 

      2.0 x 10^11

    • D. 

      7.4 x 10^-3

    • E. 

      None of the rest

  • 19. 
    The imidazole side chain of histidine can function as either a general acid catalyst or a general base catalyst because:
    • A. 

      In the physiological pH range both H+ and OH- are present at high concentrations

    • B. 

      The imidazole group is a strong reducing agent at physiological pH

    • C. 

      One guanidine group is protonated and the other is deprotonated at physiological pH

    • D. 

      In the physiological pH range, the nitrogen in the ring can be easily protonated/deprotonated

    • E. 

      The sulfur atoms in the ring can either gain or lose a proton at physiological pH

  • 20. 
    Which of the following statements does not apply to collagen?
    • A. 

      It contains hydroxylated amino acids.

    • B. 

      The polypeptide forms a left-handed helix.

    • C. 

      Hydrogen bonds between the -OH groups of Hyp residues stabilize the helix.

    • D. 

      There is a requirement for glycine at every third position.

    • E. 

      The triple helical structure twists in the right-handed direction.

  • 21. 
    Why is the decreased affinity of fetal hemoglobin for BPG advantageous?
    • A. 

      With fewer BPG molecules bound there are more heme residues available for O2 binding.

    • B. 

      Decreased BPG binding biases the fetal hemoglobin toward the R state.

    • C. 

      More free BPG is available to bind to adult hemoglobin, resulting in a shift of adult hemoglobin to the R state.

    • D. 

      BPG is available to bind to fetal myoglobin, helping to release O2 in fetal muscle tissue.

    • E. 

      None of the rest is correct.

  • 22. 
    Which of the following is correct about amino acid side chain?
    • A. 

      The nucleophilicity of a side chain is inversely related to its acidity.

    • B. 

      The less acidic a group is, the more nucleophilic it is.

    • C. 

      The more basic a group is, the more likely it is to react with an electrophilic group.

    • D. 

      The more electron-rich a group is, the more likely it is to react with an electrophilic group.

    • E. 

      All of the rest are correct.

  • 23. 
    Lysozyme catalyzes the hydrolysis of a polysaccharide component of bacterial cell walls. The damaged bacteria subsequently lyse (rupture). Part of lysozyme's mechanism is shown in Figure 1. The enzyme catalyzes cleavage of a bond between two sugar residues (represented by hexagons). Catalysis involves the side chains of Glu 35 and Asp 52. One of the residues has a pK of 4.5; the other has a pK of 5.9. Which of the following statements is correct?
    • A. 

      Glu 35 has a pK of 5.9 and Asp52 has a pK of 4.5

    • B. 

      Glu 35 has a pK of 4.5 and Asp52 has a pK of 5.9

    • C. 

      Lysozyme is inactive at pH 2.0 because both the Glu and the Asp are deprotonated

    • D. 

      Lysozyme is inactive at pH 8.0 because the Asp would be unable to donate a hydrogen to cleave the bond between the sugar residues.

    • E. 

      All of the rest are correct

  • 24. 
    Hydrophobic residues usually appear at the first and fourth positions in the seven-residue repeats of polypeptides that form coiled coils. The first and fourth side chains are buried in the coiled coil, but the remaining side chains are exposed to the solvent and therefore tend to be polar or charged. Which of the following sequences is more likely to appear in a coiled coil?
    • A. 

      Ile-Gln-Glu-Val-Glu-Arg-Asp

    • B. 

      Trp-Gln-Glu-Tyr-Glu-Arg-Asp

    • C. 

      Ile-Gln-Glu-Val-Glu-Ala-Asp

    • D. 

      Trp-Gln-Glu-Tyr-Glu-Ala-Asp

    • E. 

      Gly-Pro-Hyp-Gly-Pro-Hyp-Gly (Hyp = hydroxyproline)

  • 25. 
    According to Figure 3, which of the following is not likely to be a serine protease zymogen?
    • A. 

      Factor XI

    • B. 

      Factor IX

    • C. 

      Factor X

    • D. 

      Prothrombin

    • E. 

      Fibrinogen