Deck 7: Protein Function Part I: Myoglobin and Hemoglobin

Question 1

Matching

In the ______ state of hemoglobin,the iron ion is out of the plane of the porphyrin ring.

A) positively cooperative
B) cyanosis
C) His E7
D) decrease
E) R
F) hydrogen bonds
G) increase
H) symmetry
I) His F8
J) ion pairs
K) T
L) hemolytic anemia
M) sequencial

Answer 1

T

Question 2

Hemoglobin is a heterotetramer.How many protomers are present in hemoglobin?

A)0
B)1
C)2
D)3
E)4

Answer 2

2

Question 3

Matching

Mutations that favor the oxidation of the heme iron(II)to iron(III)can cause ______.

A) positively cooperative
B) cyanosis
C) His E7
D) decrease
E) R
F) hydrogen bonds
G) increase
H) symmetry
I) His F8
J) ion pairs
K) T
L) hemolytic anemia
M) sequencial

Answer 3

cyanosis

Question 4

Myoglobin's secondary structure is primarily composed of ______________.

A)"parallel $\beta$ -sheets"
B)"antiparallel $\beta$ -sheets"
C)" $\alpha$ -helices"
D)" $\Omega$ -loops"
E)"polyproline helices"

Question 5

Which gas does not bind to the porphyrin ring Fe(II)ion in myoglobin?

A)NO
B)CO
C)CO₂
D)O₂
E)H₂S

Question 6

Which of the following is not a ligand to the porphyrin ring Fe(II) ion in oxymyoglobin?

A)His E7
B)His F8
C)Nitrogen atoms in the porphyrin ring
D)Oxygen
E)all are ligands

Question 7

Matching

When unstable hemoglobin is degraded;degradation products often cause cell lysis,leading to a condition called ______.

A) positively cooperative
B) cyanosis
C) His E7
D) decrease
E) R
F) hydrogen bonds
G) increase
H) symmetry
I) His F8
J) ion pairs
K) T
L) hemolytic anemia
M) sequencial

Question 8

The primary structure of mammalian hemoglobin,an $\alpha$ ₂ $\beta$ ₂ tetramer,is approximately _____ identical to myoglobin.

A)2%
B)18%
C)50%
D)78%
E)98%

Question 9

Matching

The ______ model of allosterism requires subunits to change conformation simultaneously.

A) positively cooperative
B) cyanosis
C) His E7
D) decrease
E) R
F) hydrogen bonds
G) increase
H) symmetry
I) His F8
J) ion pairs
K) T
L) hemolytic anemia
M) sequencial

Question 10

Myoglobin and a single chain of hemoglobin have similar ______ structures.

A)primary
B)secondary
C)tertiary
D)quaternary
E)none of the above

Question 11

Which of the following statements does not apply to the K value in the equation for the oxygen binding curve of myoglobin?

A)It is numerically equal to p₅₀.
B)It is defined as that oxygen partial pressure at which half of the oxygen binding sites are occupied.
C)It is a measure of the affinity of myoglobin for oxygen.
D)If Y > K,then myoglobin is less than 50% saturated with oxygen.
E)It is the value of pO₂ at which Y = 0.5.

Question 12

Myoglobin's primary physiological role is to facilitate oxygen ________.

A)storage
B)metabolism
C)binding
D)reduction
E)diffusion

Question 13

Matching

Hemoglobin's subunits bind oxygen in a ______ manner.

A) positively cooperative
B) cyanosis
C) His E7
D) decrease
E) R
F) hydrogen bonds
G) increase
H) symmetry
I) His F8
J) ion pairs
K) T
L) hemolytic anemia
M) sequencial

Question 14

If the gene for myoglobin is "knocked out" in mice,the mice:

A)have larger lungs.
B)respire extremely rapidly.
C)have dark brown muscle tissue.
D)appear normal,with lighter colored muscle tissue.
E)have their growth stunted.

Question 15

Matching

When oxygen binds to heme,the oxygen forms a hydrogen bond with ______.

A) positively cooperative
B) cyanosis
C) His E7
D) decrease
E) R
F) hydrogen bonds
G) increase
H) symmetry
I) His F8
J) ion pairs
K) T
L) hemolytic anemia
M) sequencial

Question 16

Matching

An increase in pCO₂ causes hemoglobin's affinity for oxygen to ______.

A) positively cooperative
B) cyanosis
C) His E7
D) decrease
E) R
F) hydrogen bonds
G) increase
H) symmetry
I) His F8
J) ion pairs
K) T
L) hemolytic anemia
M) sequencial

Question 17

Matching

The conversion of hemoglobin from the T to the R state requires breaking of ______ involving C-terminal residues.

A) positively cooperative
B) cyanosis
C) His E7
D) decrease
E) R
F) hydrogen bonds
G) increase
H) symmetry
I) His F8
J) ion pairs
K) T
L) hemolytic anemia
M) sequencial

Question 18

Carbon monoxide binds to heme:

A)with a higher affinity than oxygen.
B)resulting in the oxidation of the Fe(II)to Fe(III)
C)in a manner that displaces carbon dioxide,causing CO₂ poisoning.
D)from the side opposite oxygen,resulting in a brown colored heme.
E)with a lower affinity than oxygen.

Question 19

Matching

Sickle cell hemoglobin does not form fibers in the ______ form.

A) positively cooperative
B) cyanosis
C) His E7
D) decrease
E) R
F) hydrogen bonds
G) increase
H) symmetry
I) His F8
J) ion pairs
K) T
L) hemolytic anemia
M) sequencial

Question 20

Matching

The absence of 2,3-BPG causes hemoglobin's affinity for oxygen to______.

A) positively cooperative
B) cyanosis
C) His E7
D) decrease
E) R
F) hydrogen bonds
G) increase
H) symmetry
I) His F8
J) ion pairs
K) T
L) hemolytic anemia
M) sequencial

Question 21

The oxygen binding by hemocyanins is mediated by

A)an iron ion
B)a pair of iron ions
C)a heme group
D)a copper atom
E)a pair of copper atoms

Question 22

Which of the following statements about the symmetry model of allosterism is not true?

A)the protein is an oligomer of symmetrically (or pseudosymmetrically)related subunits.
B)the oligomer can exist in two conformational states,which are in equilibrium.
C)the ligand can bind to a subunit in either conformation.
D)the molecular symmetry of the protein is conserved during the conformational change.
E)none of the above.

Question 23

The Bohr effect refers to

A)the decrease in affinity of Hb for O₂ when the pH goes down
B)the decrease in affinity of Hb for O₂ when the pH goes up
C)the increase in the affinity of Hb for O₂ when the O₂ concentration goes up
D)the decrease in affinity of Hb for O₂ when the BPG concentration goes up
E)the decrease in affinity of Hb for O₂ when the BPG concentration goes down

Question 24

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 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 above

Question 25

The most rapid way that erythrocytes adapt to high altitudes is

A)by producing genetically altered hemoglobins that have higher O₂-binding affinities.
B)by adopting the symmetry model of allosterism.
C)by increasing the concentration of hemoglobin.
D)by relying upon the simpler protein myoglobin.
E)by increasing the intracellular concentration of BPG.

Question 26

Max Perutz's investigation of the structure of hemoglobin primarily utilized_____.

A)X-ray crystallography
B)NMR spectroscopy
C)genomics
D)mass spectrometry
E)genetic engineering

Question 27

The Hill plot shows that the fourth oxygen binds to hemoglobin with a ______-fold greater affinity than the first.

A)2
B)5
C)10
D)20
E)100

Question 28

The reaction of carbonic anhydrase catalyzes

A)the formation of carbamates with the concomitant release of protons.
B)the hydration of bicarbonate,resulting in the formation of carbonic acid.
C)the reduction of carbon dioxide with the concomitant consumption of protons.
D)the hydration of carbon dioxide,forming bicarbonate and protons.
E)the hydrolysis of carbamates with the concomitant consumption of protons.

Question 29

What is the type of symmetry that relates the protomers in hemoglobin with respect to each other?

A)C₂
B)C₄
C)D₂
D)D₄
E)Tetrahedral symmetry

Question 30

During the T to R conformational shift,Fe(II)drags the F-helix via a bond to the side chain of ________.

A)Leu F7
B)Leu F4
C)His F8
D)Leu FG3
E)Val FG5

Question 31

Hemoglobin's p₅₀ value is about ______ as great as myoglobin's p₅₀ value.

A)one-tenth
B)half
C)twice
D)ten times
E)twenty times

Question 32

When the partial pressure of O₂ in venous blood is 30 torr,the saturation of myoglobin with O₂ is ______ while the saturation of hemoglobin with O₂ is ______.

A)0)55,0.91
B)0)91,0.55
C)2)8 torr,26 torr
D)0)91,0.97
E)none of the above

Question 33

The rearrangement of T state hemoglobin to the R state

A)occurs in each protein subunit independently when its heme binds oxygen.
B)requires the binding of at least three oxygen molecules.
C)increases the ion pairing interactions of the C-terminal amino acids.
D)involves the movement of the Fe(II)into the heme plane.
E)opens a central cavity for BPG binding.

Question 34

While the binding of O₂ to myoglobin as a function of pO₂ is described by a simple __________ curve,the binding to hemoglobin is described by a more complex ______ curve.

A)sigmoidal;hyperbolic
B)hyperbolic;sigmoidal
C)exponential;hyperbolic
D)sigmoidal;bell-shaped
E)hyperbolic;concave

Question 35

Some abnormal hemoglobins have Hill coefficients that are ______ that of normal hemoglobin,indicating that their ability to bind oxygen cooperatively has been compromised.

A)less than
B)greater than
C)much greater than
D)about equal to
E)The correct answer cannot be determined from the information given.

Question 36

Hemerythrin and hemocyanin are:

A)human mutant hemoglobins with decreased oxygen affinity.
B)hemoglobin variants that are found in animals at high altitude.
C)synthetic derivatives of hemoglobin's heme group used in artificial blood substitutes.
D)oxygen transport proteins found in invertebrates.
E)tetrameric hemoglobin derivatives containing only $\alpha$ -chains ( $\alpha$ ₄ tetramers).

Question 37

The value of n,the Hill constant (coefficient),for hemoglobin is about ______ as great as the value for myoglobin.

A)half
B)twice
C)three times
D)five times
E)ten times

Question 38

Which of the following increases the affinity of hemoglobin for O₂?

A)an increase in BPG concentration
B)the formation of N-terminal carbamates
C)an increase in pH
D)a decrease in pH
E)an increase in CO₂ concentration

Question 39

Consider a hypothetical hemoglobin-like molecule with a Hill coefficient (constant)of 1 and the same p₅₀ value as normal hemoglobin.Choose the statement below that best describes the two proteins.

A)There is a cooperative interaction between oxygen-binding sites in both the hypothetical and normal hemoglobins.
B)The hypothetical hemoglobin has a greater oxygen affinity than normal hemoglobin.
C)The oxygen binding curve for the hypothetical hemoglobin is hyperbolic,and the curve for normal hemoglobin is sigmoidal.
D)The two hemoglobins would be able to deliver about the same amount of oxygen to the tissues.
E)At pO₂ less than p₅₀,normal hemoglobin has a greater Y_O2 value.

Question 40

BPG stands for

A)biphenylglycine.
B)boronylphenylglutamate.
C)bisphosphoglycerate.
D)bisphenylglycerol.
E)betapropylglutamine.

Question 41

During muscle contraction myosin heads

A)walk along thick filaments toward the M disk.
B)walk along thick filaments toward the Z disk.
C)walk along thin filaments toward the M disk.
D)walk along the thin filaments toward the H zone.
E)walk along the thin filaments toward the Z disk.

Question 42

Which of the statements about muscle contraction is not true?

A)During muscle contraction the sarcomere becomes shorter.
B)During muscle contraction the I band becomes shorter.
C)During muscle contraction the H zone becomes shorter.
D)During muscle contraction the A band becomes shorter
E)During muscle contraction the distance between the Z disk and the M disk becomes shorter.

Question 43

Which statement about myosin is not true?

A)Myosin is a heterohexamer.
B)Myosin contains two globular heads.
C)Myosin contains six different polypeptides
D)Myosin aggregates to form thick filaments
E)All of the answers above are true of myosin.

Question 44

Muscle contraction is triggered

A)in response to an increase in the cytoplasmic Ca²⁺ concentration.
B)in response to a decrease in the cytoplasmic Ca²⁺ concentration.
C)in response to an increase in the cytoplasmic cAMP concentration.
D)in response to a decrease in the cytoplasmic cAMP concentration.
E)in response to an increase in the cytoplasmic titin concentration.

Question 45

______of the world's human population carries an inherited variant hemoglobin gene.

A)5%
B)25%
C)50%
D)75%
E)90%

Question 46

During muscle contraction

A)myosin pulls actin filaments toward the M disk.
B)myosin pushes actin filaments toward the Z disk.
C)actin pulls myosin toward the Z disk.
D)actin pushes myosin toward the M disk.
E)All of the answers above are correct.

Question 47

Humoral immunity refers to that part of the immune response that is mediated by

A)T lymphocytes.
B)antibodies.
C)antigens.
D)the thymus.
E)the skin.

Question 48

Humoral immunity is mediated by soluble molecules.Which cell type produces the soluble molecules that carry out the humoral immunity?

A)T cells
B)B cells
C)macrophages
D)neutrophils
E)monocytes

Question 49

Muscle contraction is directly caused by

A)structural changes in actin.
B)structural changes in myosin.
C)thick and thin filaments sliding past each other.
D)structural changes in the Z disk.
E)None of the above is correct.

Question 50

Treadmilling refers to

A)myosin heads walking along actin microfilaments.
B)actin and myosin filaments sliding along each other.
C)actin monomers moving through a microfilament from the + end to the - end.
D)synthesis and degradation of actin monomers.
E)the interactions between actin and tropomyosin.

Question 51

Which statement about actin is correct?

A)Actin is expressed only in muscle.
B)Actin is expressed at low levels in most cells.
C)No known function has been described for actin in nonmuscle cells.
D)Nonmuscle cells only contain G actin.
E)Actin is the most abundant cytoplasmic protein in many cell types.

Question 52

Which statement about actin is not true?

A)There are two actin genes,one for F-actin and one for G-actin.
B)Monomeric G-actin polymerizes to form F-actin.
C)Actin filaments are polar (the ends can be distinguished)
D)Actin can bind ATP.
E)Actin is a common protein in nonmuscle cells.

Question 53

Which of the statements about muscle contraction is correct?

A)During muscle contraction the sarcomere becomes shorter.
B)During muscle contraction the I band becomes shorter.
C)During muscle contraction the H zone becomes shorter.
D)During muscle contraction the distance between the Z disk and the M disk becomes shorter.
E)All of the answers above are correct.

Question 54

The energy needed to drive muscle contraction comes from ATP hydrolysis that is carried out by

A)G-actin.
B)F-actin.
C)myosin heads.
D)myosin tails.
E)tropomyosin.

Question 55

What are the main bonds or forces that stabilize the dimer formed by two myosin heavy chains?

A)hydrophobic interactions
B)hydrogen-bonds
C)ionic interactions
D)disulfide bonds
E)isopeptide bonds

Question 56

In sickle-cell anemia,the negatively charged glutamic acid residue is replaced by the neutral amino acid ____________.

A)tyrosine
B)lysine
C)valine
D)adenosine
E)glycine

Question 57

How many different classes of antibodies are produced by the human immune system?

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

Question 58

Muscle contraction is directly caused by

A)structural changes in actin.
B)structural changes in myosin.
C)structural changes in the A band.
D)structural changes in the Z disk.
E)None of the above is correct.

Question 59

Which of the following statements about actin is not true?

A)Actin is the most abundant cytoplasmic protein in many cell types.
B)Actin forms microfilaments in many cell types.
C)Actin plays an important role in endocytosis.
D)Actin is present only as monomers in nonmuscle cells.
E)Actin filaments are dynamic,they grow at one end and they lose subunits at the other end.

Question 60

Hemoglobin S,the variant responsible for the misshapen red blood cells characteristic of the disease sickle-cell anemia,is potentially advantageous to heterozygotes because it confers some level of resistance to the disease _________.

A)rickets
B)AIDS
C)cyanosis
D)polycythemia
E)malaria

Question 61

The Ig fold can be described as a

A)globular fold composed of $\alpha$ helices.
B)a globular fold composed of a four helix bundle.
C)a globular fold composed of a $\beta$ sandwich.
D)a globular fold composed of $\beta$ barrel.
E)a coiled-coil.

Question 62

IgG is one of five classes of antibodies that can be produced by our immune system.IgGs have a molecular mass of approximately 150 kDa,what is their subunit composition?

A)2 light chains and 2 heavy chains
B)2 light chains,2 heavy chains,and a J chain
C)4 light chains,4 heavy chains,and a J chain
D)6 light chains,6 heavy chains,and a J chain
E)10 light chains,10 heavy chains ,and a J chain.

Question 63

The graph below shows the O₂-binding curves for myoglobin (Mb)and hemoglobin (Hb).
a.Label the two curves (indicate which one represents Mb and which one represents Hb).
b.Use the graph to determine the K_d of myoglobin for O₂ (show your approach).
c.What is the difference between myoglobin and hemoglobin that cause the O₂-binding curves to so be different?
d.Why is it important that hemoglobin has these particular O₂-binding characteristics?

Question 64

Which statement about antigen-binding sites in antibodies is false?

A)An antigen-binding site on an IgG is formed by the amino-terminal ~110 amino acids of a light chain and the amino terminal ~110 amino acids of a heavy chain.
B)An antigen-binding site on an IgG is formed by the variable region of a light chain and the variable region of a heavy chain.
C)The antigen-binding site is composed of two Ig folds.
D)Antigen-binding specificity is determined by the sequences of the hypervariable sequences in both the light chain and the heavy chain.
E)Antigen binding specificity is determined exclusively by the sequences in the carboxy-terminal ~110 amino acids in the light chain and the heavy chain.

Question 65

Which class of antibodies has been implicated in allergic reactions?

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

Question 66

How many antigen-binding sites are present on an IgG molecule?

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

Question 67

Fab fragments can be generated by

A)reduction of IgG molecules.
B)oxidation of IgG molecules.
C)limited digestion of IgG molecules with papain.
D)combining two light chains.
E)combining two heavy chains.

Question 68

What is the primary physiological function of myoglobin in most mammals?

Question 69

Myoglobin is an oxygen binding protein in muscle.Describe in one sentence the overall structure of myoglobin.

Question 70

You have been studying O₂ binding to a hemerythrin-like protein isolated from an exotic marine worm.Your O₂-binding data are shown in the table below.
a.Use the data to generate an O₂-binding curve (do not forget to mark the axes).
b.Use the curve to estimate the K_d for the interaction.
c.Is there any evidence from your data that this hemoglobin-like protein binds O₂ in a cooperative manner (briefly explain your answer)?

Question 71

Mammals and other animals have a circulatory system because diffusion is to slow to supply the tissues with oxygen in animals that are larger than 2 millimeter.Explain in one sentence why these circulatory systems contain hemoglobin or other oxygen binding proteins?

Question 72

How many antigen-binding sites are present on an IgM molecule?

A)2
B)4
C)10
D)16
E)25

Question 73

IgG is the most common immunoglobulin in the circulatory system and in the extravascular fluid.It is composed of two light chains and two heavy chains.What is the approximate molecular mass of an IgG molecule?

A)23 kDa
B)75 kDa
C)150 kDa
D)360 kDa
E)950 kDa

Question 74

It appears that the heme group in myoglobin binds the O₂.What is the function of the polypeptide?