Protein Function MCQ

• Every third residue in the protein collagen is ________.

  A)glycine

  B)phenylalanine

  C)tryptophan

  D)tyrosine

  A
• In haemoglobin, the transition from a low-affinity state to high-affinity state is triggered by:

  A)Fe 2+ binding.

  B)haem binding.

  C)oxygen binding.

  D)subunit association.

  E)subunit dissociation.


  C
• In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as:

  A)hyperbolic.

  B)linear with a negative slope.

  C)linear with a positive slope

  D)random.

  E)sigmoidal.

  A
• Myoglobin and the subunits of haemoglobin have:

  A)no obvious structural relationship.

  B)very different primary and tertiary structures.

  C)very similar primary and tertiary structures.

  D)very similar primary structures, but different tertiary structures.

  E)very similar tertiary structures, but different primary structures.

  E
• The amino acid substitution of valine for glutamate in Haemoglobin S results in aggregation of the protein because of ___________ interactions between molecules.

  A)covalent

  B)disulphide

  C)hydrophobic

  D)hydrogen bonding

  E)ionic

  C
• The fundamental cause of sickle-cell disease is a change in the structure of:

  A)blood.

  B)capillaries.

  C)haemoglobin.

  D)red blood cells.

  E)the heart.

  C
• What is the Bohr effect?

  A)the ability of haemoglobin to retain oxygen when in competition with myoglobin

  B)the regulation of haemoglobin-binding by hydrogen ions and carbon dioxide

  C)the alteration of haemoglobin conformation during low oxygen stress

  D)All of the above answers are correct.

  E)None of the above answers are correct.

  B
• What type of binding is indicated by a sigmoidal-shaped binding curve?

  cooperative
• Which of the following is correct concerning the differences between haemoglobin and myoglobin?

  A)Both haemoglobin and myoglobin are tetrameric proteins.

  B)Haemoglobin exhibits a higher degree of O2 saturation at all physiologically relevant partial pressures of O2 than does myoglobin.

  C)Haemoglobin exhibits a hyperbolic O2 saturation curve while myoglobin exhibits a sigmoid shaped curve.

  D)Haemoglobin exhibits cooperative binding of O2 while myoglobin does not.

  E)All of the answers are correct.

  D
• Why is the sickle-cell haemoglobin mutation so prevalent in Africa and other tropical regions?

  A)Bonding of carbon dioxide to sickle-cell haemoglobin molecules increases the binding of oxygen.

  B)Haemoglobin binds more oxygen with aggregations of α chains found in sickle-cell haemoglobin.

  C)People with the sickle-cell trait are resistant to malaria, increasing the prevalence of the sickle-cell haemoglobin allele.

  D)The oxygen binds with greater affinity to the proximal histidine residue of sickle-cell haemoglobin.

  C
• ________ is the major fibrous protein present in skin, bone, tendon, cartilage, and teeth.

  A)α-Keratin

  B)Actin

  C)Collagen

  D)Fibroin

  C
• _________ is a fibrous protein and is the primary component of wool and hair.

  A)α-Keratin

  B)actin

  C)collagen

  D)fibroin

  E)myosin

  A
• Which of the following is NOT correct concerning myoglobin?

  A)The globin chain contains an extensive α-helix structure.

  B)The haem group is bound to the globin chain by two disulfide bonds to cysteine residues.

  C)The iron of the haem group is in the Fe2+ oxidation state.

  D)The diameter of the iron ion decreases upon binding to oxygen.

  E)The function of myoglobin is oxygen storage in muscle.

  B
• Which of the following is correct concerning the oxygenation plot of proteins X and Y shown below?

  A)Protein X contains multiple binding sites.

  B)Protein X exhibits cooperative binding, whereas Y does not.

  C)Protein Y corresponds to myoglobin, and protein X corresponds to haemoglobin.

  D)Protein Y exhibits tighter oxygen-binding than protein X.

  E)Protein Y would function as a better oxygen-transport protein than protein X

  E

  
• Consider the oxygen-binding profile at three different pH values of 7.6, 7.4, and 7.2. Which statement is correct?

  A)Curve X most likely corresponds to pH 7.2.

  B)Curve Z most likely corresponds to pH 7.6.

  C)Hemoglobin has a higher affinity for oxygen at the pH of curve Z.

  D)Curve Y most likely corresponds to pH 7.4.

  E)pH has no effect on the oxygenation of hemoglobin.

  D

  
• When oxygen binds to a haem-containing protein, the two open coordination bonds of Fe2+ are occupied by:

  A)one O atom and one amino acid atom.

  B)one O2 molecule and one amino acid atom.

  C)one O2 molecule and one heme atom.

  D)two O atoms.

  E)two O2 molecules.

  B