Deck 9: Protein II: Structure-Function Relationships in Protein Families

Question 1

Which of the following functional groups of hemoglobin can bind either carbon dioxide or protons?

A) certain terminal amino groups.
B) histidine l46.
C) the C-terminal carboxyl group.
D) the heme moiety.
E) None of the above is correct.

Answer 1

certain terminal amino groups.

Question 2

Which one of the following conditions promotes association of oxygen with hemoglobin?

A) Low PO₂.
B) Low PCO₂.
C) Low pH.
D) High 2,3 diphosphoglycerate.
E) High total CO₂ content.

Answer 2

Low PCO₂.

Question 3

During vigorous physical activity, the Bohr effect would enhance the delivery of oxygen to the tissues of the body. All of the following are associated with this effect at the tissues EXCEPT

A) a conformational change occurs that alters the pKa and hence the charge on the imidazole groups of the hemoglobin molecules.
B) the oxygen-hemoglobin association curve shifts to the right.
C) the tense form of hemoglobin is stabilized.
D) hydrogen ions are released from the hemoglobin to the tissues.
E) there are alterations in the salt linkages of the hemoglobin molecules.

Answer 3

hydrogen ions are released from the hemoglobin to the tissues.

Question 4

The antigen binding site of an immunoglobulin is located within the

A) carbohydrate residues attached to the protein molecule.
B) immunoglobulin domains of the light chains.
C) hinge regions of the heavy chains.
D) variable regions of the heavy and light chains.
E) Fc fragment of the protein molecule.

Question 5

One principal function of complement is to

A) inactivate perforins.
B) mediate the release of histamine.
C) bind antibodies attached to cell surfaces and to lyse these cells.
D) phagocytize antigen.
E) cross-link allergens.

Question 6

The part of the antigen that is recognized by the antibody is called

A) the variable region.
B) the hypervariable region.
C) the constant region.
D) an epitope.
E) the immunoglobulin fold.

Question 7

The quaternary structure of hemoglobin is

A) not important for the functioning of this protein.
B) rigid and is not affected by oxygen binding.
C) maintained by hydrophobic bonds, salt bridges, and hydrogen bonds.
D) stabilized by disulfide bridges.
E) none of the above

Question 8

The AB-sites (antigen reactive sites) are located on which of the following portions of the immunoglobulin chains?

A) VL + CH
B) VL + CL
C) VL + FC
D) VL + VH
E) VH + CL

Question 9

The predominant class of antibody produced in the primary immune response is

A) IgM
B) IgG
C) IgD
D) IgA
E) IgE

Question 10

Generation of antibody diversity is primarily caused by

A) Covalent modification of immunoglobulin proteins.
B) Differences in splicing of the primary RNA transcripts of antibody genes.
C) Rearrangement of DNA.
D) DNA recombination in response to particular antigens.
E) Specific folding of antibody-combining sites induced by particular antigens.

Question 11

The difference in P50 values of fetal and adult hemoglobins is best explained by a difference in the

A) binding of nitric oxide.
B) extent of subunit cooperativity.
C) interaction with an allosteric effector.
D) number of alpha-globin subunits.

Question 12

The Bohr effect is due in part to

A) relatively low pKa (i.e. weaker base) for histidyl residues because of their proximity to ionized aspartyl residues in oxyhemoglobin.
B) a relatively high pKa (i.e. stronger base) for histidyl residues because of their proximity to arginyl residues in deoxyhemoglobin.
C) a relatively high pKa for histidyl residues because of their proximity to ionized aspartyl residues in deoxyhemoglobin.
D) a relatively low pKa for histidyl residues because of their proximity to arginyl residues in deoxyhemoglobin.

Question 13

Which of the following is a characteristic of hemoglobin?

A) It is composed of four identical polypeptide chains.
B) There is one heme group per active Hb molecule.
C) Oxygen and carbon dioxide compete for the same binding site on heme.
D) It is an elongated, fibrous-type protein, hence is not very soluble in water.
E) Binding of oxygen to Hb results in change in the pKa of certain histidine residues toward lower values.

Question 14

78Fetal hemoglobin has a higher affinity for O₂ than adult hemoglobin. This is due to

A) increased number of salt bridges between alpha and beta chains.
B) increased ability to bind to 2,3-bisphosphoglycerate (BPG).
C) decreased ability to bind to BPG.
D) decreased affinity for CO₂.
E) increased Bohr effect.

Question 15

Basement membrane is composed of basal lamina and another component. What is this other component?

A) Fibrillar collagen
B) Fibrinogen
C) Heparin sulfate
D) Proteases
E) Proteoglycan

Question 16

How are serine proteases regulated to cleave some peptide bonds more frequently than others?

A) Substrate conformation changes to hide certain cleavage sites on binding to enzyme
B) Small molecules block some sites
C) The enzyme dimerizes around the substrate
D) There is a b-pleated sheet interaction between enzyme and substrate
E) Zymogen can be activated only at certain sites

Question 17

The sigmoid (S-shaped) binding curve that describes the interaction of O₂ with hemoglobin is a direct consequence of

A) allosteric regulation by 2,3-bisphosphoglycerate.
B) cooperativity among subunits.
C) covalent bonds between alpha beta?heterodimers.
D) orientation of histidine residues near the heme groups.
E) reversible oxidation and reduction of heme iron atoms.

Question 18

Which of the following hemoglobins normally predominates at the time of birth?

A) alpha2,epsilon2
B) alpha2,gamma2
C) alpha2,beta2
D) alpha2,delta2

Question 19

All of the following are true of the isohydric mechanism EXCEPT:

A) it results in no change in intra-erythrocyte pH
B) it is responsible for accommodating 40% of the hydrogen ions generated during CO₂ transport
C) it is linked to oxygen uptake and release
D) it is responsible for the chloride shift

Question 20

Light chains of immunoglobulins

A) are specific for each class of antibody
B) are not specific for each class of antibody
C) react with antigen
D) have only a constant region
E) consist only of carbohydrate

Question 21

Similarities among the immunoglobulin domains in the light chains of immunoglobulin G include all of the following EXCEPT

A) a disulfide bond stabilizes the structure.
B) amino acid sequences are similar but not identical.
C) complementarity determining regions are located between beta?strands.
D) each domain folds independently from the others.
E) the secondary structure is dominated by beta?sheets.

Question 22

Normal hemoglobin molecules may consist of each of the following EXCEPT which one?

A) 2 alpha and 2 beta chains
B) 2 alpha and 2 delta chains
C) 2 beta and 2 delta chains
D) 2 alpha and 2 gamma chains
E) 2 alpha and 2 epsilon chains

Question 23

The regions of variable amino acid composition of immunoglobulins occur in

A) heavy chains only.
B) light chains only.
C) both light and heavy chains.
D) IgG but not other immunoglobulins.
E) IgE but not other immunoglobulins.

Question 24

Oxygen dissociation from Hb is facilitated by all of the following EXCEPT which one?
Oxygen dissociation from Hb is facilitated by all of the following EXCEPT which one?

A) low PO2
B) high PCO2
C) high temperature
D) high pH
E) high levels of 2,3-BPG

Question 25

The association of O₂ with deoxy-myoglobin

A) causes a 60 degree rotation of the porphyrin ring.
B) is accompanied by the dissociation of 2,3-bisphosphoglycerate.
C) leads to the reduction of the heme Fe ³⁺ to Fe ²⁺.
D) pulls the iron ion into the plane of the porphyrin ring.
E) replaces the distal histidine residue in the iron coordination system.

Question 26

In the normal red blood cell, 2,3-BPG binds to alpha-amino groups of hemoglobin. What would happen to the O2-saturation curve of Hb in the presence of normal amounts of 2,3-BPG if a drug were administered that prevents the binding of 2,3-BPG to Hb?

A) the curve would be shifted to the left from that of normal red cells
B) the concentration of O₂ necessary to saturate Hb would be lower than that normally required
C) the amount of O₂ delivered to the tissue for a given partial pressure of O₂ (e.g., 40 mm Hg) would be lower than normal
D) all of the above
E) none of the above

Question 27

Which portion of the immunoglobulin molecule contains the variable region with respect to primary structure?

A) The NH₂ terminal region of the light chains only.
B) The NH₂ terminal region of the heavy chains only.
C) The carboxy terminal region of both the light and heavy chains.
D) The NH₂ terminal region of both the light and heavy chains.
E) The carboxy terminal region of the heavy chains only.

Question 28

Which of the following statements about the interaction of heme units of hemoproteins with oxygen is correct?

A) Binding of 2,3-bisphosphoglycerate (BPG) to hemoglobin leads to increased binding of oxygen.
B) Binding of oxygen to one myoglobin increases the strength of binding of oxygen to other myoglobins.
C) In blood of peripheral tissues, the loss of an oxygen by a heme unit is balanced stoichiometrically by the loss of one hydrogen.
D) The binding of oxygen by separated beta-chains of hemoglobin is described by a sigmoid curve.
E) As oxygen binds to hemoglobin, the pKa's of certain amino acid sidechains decrease.

Question 29

Which of the following is TRUE of Fc receptors for immunoglobulins?

A) They are found on cells of the reticuloendothelial system and are involved in antibody-dependent, cell-mediated cytotoxicity.
B) They are associated with the T3 complex of the T-cell receptor.
C) They are not able to bind immunoglobulin.
D) They are receptors which recognize the Fab portion of the antibody.
E) They are all unique, because each has a specific antigen binding capacity.

Question 30

All of the following are true regarding IgM's EXCEPT which one?

A) They have a short half-life.
B) They are the first to be synthesized after antigenic stimulation.
C) They cross the placenta.
D) They are present mainly in plasma.
E) They consist of several subunits.

Question 31

The heme group of myoglobin

A) contains ferric ion.
B) is bound to the polypeptide chain exclusively by interactions between polar groups.
C) binds oxygen in an allosteric manner.
D) is identical to that of hemoglobin.
E) is bound to the polypeptide chain exclusively by interactions between nonpolar groups.

Question 32

The dissociated subunits of hemoglobin have a much higher affinity for oxygen than the intact molecule. Which of the following is the most likely explanation?

A) BPG can interact much more readily with the dissociated subunits.
B) The iron atom moves out of the plane of the heme.
C) The heme dissociates from the globin.
D) The Bohr effect operates more effectively.
E) The allosteric effects reducing oxygen affinity require the intact tetramer.

Question 33

What form does collagen IV in basal lamina take?

A) Barrel
B) Fibrils
C) Globin fold
D) Globular
E) Sheet-like

Question 34

How do bacterial serine proteases differ from their eukaryotic orthologs?

A) The catalytic triad has different amino acids
B) They are not inhibited by diisopropylfluorophospate
C) They are not synthesized as zymogens
D) They have only one catalytic domain
E) They show no homology with mammalian serine proteases

Question 35

The heme molecule in myoglobin is an example of a ________________.

A) secondary structure
B) quaternary structure
C) tertiary structure
D) prosthetic group
E) positive allosteric regulator

Question 36

The major immunoglobulin family to which a particular immunoglobulin belongs can be determined by sequential analysis of the 100 amino acids beginning from the

A) amino-terminal of the light chain.
B) carboxy-terminal of the light chain.
C) amino-terminal of the heavy chain.
D) carboxy-terminal of the heavy chain.
E) none of the above

Question 37

Deoxyhemoglobin contains:

A) Fe²⁺
B) CO
C) H₂0 bound to Fe³⁺
D) four beta chains
E) fewer protons than oxyhemoglobin.

Question 38

Which of the following features of the hemoglobin molecule is considered part of its secondary structure?

A) subunit interactions
B) sequence of amino acids
C) alpha helices
D) ligand binding properties
E) electrophoretic mobility

Question 39

In the typical globin protein, the conserved proximal histidine residue participates in the

A) binding of a proton as an allosteric effector.
B) coordination of the iron component of heme.
C) discrimination in binding between O2 and CO.
D) reversible formation of a carbamate.

Question 40

The complementarity-determining regions of an immunoglobulin G molecule The complementarity-determining regions of an immunoglobulin G molecule

A) are a feature of all immunoglobulin domains.
B) are located in the light but not the heavy chains.
C) participate in the covalent attachment of oligosaccharide groups.
D) specify interactions with antigens or epitopes.
E) stabilize overall protein structure.

Question 41

Carbon monoxide is toxic because

A) it is a negative allosteric effector and lowers the affinity of hemoglobin for oxygen.
B) it oxidizes Fe²⁺ (ferrous) to Fe³⁺ (ferric).
C) it reacts chemically with one of the essential amino acid sidechains and inactivates the hemoglobin.
D) it binds competitively to the heme group and thus lowers the amount of oxygen bound.

Question 42

The P50 value of hemoglobin is higher than normal in all of the following conditions EXCEPT

A) low pH.
B) high PCO₂.
C) low 2,3-bisphosphoglycerate.
D) mutant hemoglobin with low oxygen affinity.

Question 43

A principal difference between the light and heavy chains of immunoglobulins is

A) attachment of lipid anchors.
B) modification by oligosaccharides.
C) origin from different genetic elements.
D) presence of variable domains.
E) stabilization by disulfide bonds.

Question 44

Which of the following statements about hemoglobin is true?

A) BPG decreases the affinity of hemoglobin for oxygen by stabilizing the T-state
B) BPG decreases the affinity of hemoglobin for oxygen by releasing an H⁺
C) hemoglobin is composed of 4 myoglobin molecules
D) hemoglobin binds carbon dioxide at the heme oxygen binding site
E) increased acidity increases hemoglobin's oxygen affinity

Question 45

Which basal lamina component binds cations and water to form gels that can withstand compression?

A) Collagen
B) Entactin
C) Laminin
D) Nidogen
E) Perlecan

Question 46

Laminin and fibronectin have which characteristic in common?

A) they bind collagen
B) they contain three polypeptide chains
C) they undergo covalent modification outside of cells
D) they contain a cell-binding domain characterized by an RDG sequence

Question 47

The primary function of an antibody has been fulfilled when it

A) crosses the placenta.
B) binds an antigenic determinant.
C) attaches to a mast cell.
D) activates the kinin system.
E) activates complement.

Question 48

Which of the following is true of myoglobin?

A) its Hill coefficient is less than that of hemoglobin
B) it carries the same amount of oxygen as hemoglobin on a molar basis
C) its binding of oxygen represents positive cooperativity
D) its binding of oxygen is affected by 2,3-BPG

Question 49

In the immunoglobulin G molecule disulfide bonds

A) are located within each immunoglobulin domain.
B) crosslink antigens to the antigen binding sites.
C) form between two Met residues.
D) prevent interactions with cell?surface Fc receptors.

Question 50

The following statements about hemoglobin F (fetal Hb) are all true EXCEPT

A) The P50 for O₂ is closer to 20 torr than 27 torr which is the P50 for adult Hb.
B) The beta chains are identical to those in adult hemoglobin.
C) Some terminal amino groups are acetylated.
D) The positive charges in the BPG binding cleft are fewer than in adult hemoglobin.
E) The diminished ability to unload O₂ is offset by a higher than adult concentration

Question 51

All of the following are features of the IgG molecule EXCEPT which one?

A) It contains two gamma-chains.
B) It contains either two kappa-chains or two lambda-chains.
C) Each light chain contains a constant domain and a variable domain.
D) Each heavy chain contains four constant domains.
E) There are both intrachain and interchain disulfide bonds.

Question 52

The hemoglobin variant Hb Little Rock exhibits decreased binding of 2,3-bisphosphoglycerate. The most likely consequence of this mutation is

A) altered association - dissociation of subunits.
B) decreased stability.
C) decreased oxygen affinity.
D) increased oxygen affinity.
E) increased loss of heme groups.

Question 53

What happens when the substrate for a serine protease is denatured?

A) It allows for non-specific cleavage
B) It changes the specificity for cleavage
C) It inhibits cleavage
D) It makes the serine protease an exopeptidase
E) It removes any requirement for a metal ion

Question 54

The class of an immunoglobulin

A) is determined by the Class I and Class II major histocompatibility complex proteins.
B) is determined by the carbohydrate attached to the light chain.
C) is determined by the antigen.
D) is determined by the heavy chain type.
E) is determined by the J-chain.

Question 55

Which of the following is a correct statement regarding the structure of a IgG antibody?

A) It is a protein with a small percentage of carbohydrate attached.
B) It is a carbohydrate with a small amount of protein attached.
C) It is a protein with an equal weight of carbohydrate attached.
D) It is a protein with a small amount of phospholipid attached.
E) It is a complex of protein, carbohydrate and lipid.

Question 56

Which of the following statements about the Bohr effect is TRUE?

A) Deoxyhemoglobin is a stronger acid than oxyhemoglobin.
B) The pKa for deoxyhemoglobin is less than the pKa for oxyhemoglobin.
C) hemoglobin oxygenation is favored in environments with a greater carbon dioxide concentration.
D) hemoglobin protonation favors oxygen release.

Question 57

When the oxygen-saturation curve of hemoglobin is analyzed by use of the Hill equation, a Hill constant of about 3 is found. This means that

A) only 3 of the 4 hemes can bind O2.
B) negative cooperativity causes hemoglobin to behave as if it had only 3 hemes that can bind O2.
C) each of the 4 hemes can bond O2, but not as tightly as they would in the absence of cooperativity.
D) the binding of O₂ is highly, but not perfectly, cooperative.
E) 3 of the heme groups bind O₂ equally tightly, and the 4th heme binds O₂ more tightly.

Question 58

The transition from the taut (deoxy) form of hemoglobin to the relaxed (oxy) form of hemoglobin involves the breaking of inter-subunit bonds that are predominately

A) covalent.
B) van der Waal's
C) hydrophobic
D) ionic
E) none of the above

Question 59

The combining site for antigen is formed by the

A) constant regions of the heavy chains.
B) constant regions of the light chains.
C) variable region of the light chain and the constant region of the heavy chain.
D) variable region of the light chain and the variable region of the heavy chain.

Question 60

Hemoglobin contains four polypeptide chains per molecule. As individual items, and with no other information, the best evidence for this conclusion is

A) hemoglobin contains four iron atoms per molecule.
B) a molecule of hemoglobin binds four atoms of oxygen.
C) hemoglobin crystallizes in the cubic crystal form.
D) the molecular weight of hemoglobin is 64,000.
E) there are four N-terminal valine residues per molecule of hemoglobin.

Question 61

All of the following are characteristic of the tense form of hemoglobin EXCEPT

A) Some N-terminal amino and histidine groups have lowered pKs.
B) the subunit structure is stabilized by ionic bonds.
C) the molecule can bind bis-phosphoglycerate (BPG).
D) the molecule has a reduced affinity for oxygen.
E) the molecule has an increased affinity for carbon dioxide.

Question 62

The structure of myoglobin, as determined by x-ray diffraction, exhibits all of the following EXCEPT which one?

A) The heme group is tucked into a pocket or cleft of the myoglobin molecule.
B) The myoglobin molecule has almost the same alpha helical content as the individual subunits of the hemoglobin molecule.
C) The myoglobin molecule has a very similar tertiary structure to the individual subunits of the hemoglobin molecule.
D) There is almost no water in the interior of the molecule.
E) The heme iron is linked to a tyrosine residue at its fifth coordination position.

Question 63

Which of the following immunoglobulins is present normally in plasma at the highest concentration?

A) IgA
B) IgM
C) IgG
D) IgD
E) IgE

Question 64

Which of the following participates in the reaction at the catalytic site of chymotrypsin?

A) amino ethanol
B) urea
C) pyridoxal
D) serine
E) mercaptoethanol

Question 65

The part of the antigen that is recognized by the antibody is called

A) the variable region.
B) the hypervariable region.
C) the constant region.
D) an epitope.
E) the immunoglobulin fold.

Question 66

Each of the following statements is correct EXCEPT which one?

A) Heme is the prosthetic group of myoglobin and certain cytochromes.
B) The ring structure of heme is composed of four pyrrole rings linked by one-carbon bridges.
C) In hemoglobin, one of the coordinate covalent linkages of each iron atom is to a histidine nitrogen.
D) The phenomenon of cooperativity is observed in the binding of oxygen to myoglobin.
E) The binding of BPG to beta chains of Hb decreases the affinity of alpha chains for oxygen.

Question 67

All of the following are true of IgM antibodies, EXCEPT which one?

A) They fix complement.
B) They occur on the surface of B-lymphocytes.
C) They predominate in the primary immune response to antigen.
D) They are glycoproteins.
E) They are a molecule with a single, defined amino acid sequence.

Question 68

All of the following are correct with respect to human IgE EXCEPT

A) the IgE heavy chain has 5 constant region domains.
B) IgE binds tightly to mast cell membranes.
C) the serum concentration of IgE is quite low when compared to the other immunoglobulins.
D) food-specific IgE is associated with true food allergies.
E) the reaction of a food antigen with mast cell membrane-bound IgE leads to the release of histamine and leukotrienes.

Question 69

Which of the following results in a shift of the oxyhemoglobin dissociation curve to the right?

A) An increase in 2,3-BPG
B) A decrease in temperature
C) An increase in pH
D) A decrease in PC0₂

Question 70

All of the following statements regarding the transport of carbon dioxide and molecular oxygen by hemoglobin are true EXCEPT

A) the isohydric shift is possible because deoxygenated hemoglobin is a stronger base than oxygenated hemoglobin.
B) if the tissues are using glucose only as a fuel, then the isohydric shift plus some other buffering effect of blood is necessary to prevent the pH of plasma from changing very much.
C) erythrocytes in venous blood have a lower concentration of chloride ion than when they are in the arterial system.
D) the total bicarbonate concentration in venous blood is higher than in arterial blood.
E) the PO2 and pH in venous blood tend to be lower than in arterial blood.

Question 71

The complementarity-determining regions (CDR) of human immunoglobulin G

A) are common to the general structure of all immunoglobulin domains.
B) consist of short segments of highly variable amino acid sequence.
C) form covalent complexes with antigens.
D) have been identified only on the light chain polypeptides.
E) participate in the binding of these proteins to cell surface receptors.

Question 72

Chymotrypsin and the other members of the same protease family utilize which of the following amino acid side chains at their catalytic site?

A) alanine, serine and lysine
B) aspartic acid, alanine and glutamic acid
C) aspartic acid, serine and histidine
D) glutamic acid, alanine and histidine
E) histidine, glutamic acid and lysine

Question 73

How many subunits does laminin have?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 74

Which of the following regarding 2,3-BPG is correct?

A) Increasing 2,3-BPG concentration shifts the oxyhemoglobin dissociation curve to the right.
B) It binds to the alpha-chains in the core of the hemoglobin molecule.
C) It responds rapidly to hypoxia
D) It increases the affinity of hemoglobin for oxygen

Question 75

What are the family of specific serine protease inhibitors called?

A) Acrosins
B) Cathepsins
C) Kallikreins
D) Proteins C
E) Serpins

Question 76

The fact that when a deoxyhemoglobin crystal is oxygenated it breaks up into fragments supports the statement that

A) hemoglobin is a tetramer.
B) oxyhemoglobin and deoxyhemoglobin have different conformations.
C) each subunit of hemoglobin has identical oxygen-binding sites.
D) all subunits of a hemoglobin molecule must have the same conformation at any given time.
E) each oxygen-binding site of hemoglobin is on a separate subunit.

Question 77

Similarities between hemoglobin and myoglobin include:

A) heme as a prosthetic group.
B) the effects of pH on oxygen binding.
C) the effects of BPG.
D) the shape of the oxygen dissociation curve.
E) conversion from tense to relaxed conformation at increased PO2.

Question 78

All of the following statements about the conversion of hemoglobin from taut to relaxed forms are correct, EXCEPT

A) additional inter-subunit salt bridges are formed.
B) affinity for molecular oxygen increases.
C) the subunits move relative to one another.
D) BPG is excluded from the central cavity of the molecule.
E) affinity for carbon dioxide decreases.

Question 79

Which of the following statements best characterizes an antibody?

A) An antibody contains high molecular weight RNA as its basic structure.
B) An antibody is composed of protein and cannot be distinguished from the albumin fraction of the serum proteins.
C) An antibody is composed of four identical protein subunits which may be caused to dissociate by treatment with urea.
D) An antibody contains protein as its major chemical component and its synthesis may be elicited by the administration of a foreign protein or polysaccharide.
E) An antibody contains mucopolysaccharides as its major chemical component and the synthesis of these may be elicited by the administration of a foreign protein or polysaccharide.

Question 80

Each antigen binding site of this IgG consists of amino acid residues located on

A) a light-chain constant domain and a heavy-chain variable domain.
B) a light-chain variable domain and a heavy-chain variable domain.
C) a light-chain variable domain and a heavy-chain constant domain.
D) two light-chain variable domains.
E) two heavy-chain variable domains.