Deck 6: Protein Function

Question 1

A proposed structure of a bacterial membrane protein shows that the distance between successive amino acids in a region crossing the membrane is 3.4 Å.Recall that a typical lipid bilayer is approximately 40 Å across.Which of the following is the most likely description of the protein?

A) The transmembrane region of the protein resembles the transmembrane region of the Ca²⁺-ATPase transporter protein.
B) The primary sequence of the transmembrane region of the protein is composed of approximately nine amino acids.
C) The protein contains a selectivity channel.
D) The protein resembles a porin.

Answer 1

D

Question 2

Which of the following directly requires ATP to carry out its function?

A) Cl^-ion channel
B) malate dehydrogenase
C) myoglobin
D) protein kinase A

Answer 2

protein kinase A

Question 3

Below is a fractional saturation curve for O₂ binding to adult hemoglobin.Assume that curve Y represents a system at pH 7.4 and with a normal physiological level of 2,3-BPG.Curve X represents a system that

A) is at pH 7.4 with a higher than normal physiological level of 2,3-BPG.
B) has a higher pH with a normal physiological level of 2,3-BPG.
C) has a lower pH with a normal physiological level of 2,3-BPG.
D) is at pH 7.4 with a normal physiological level of 2,3-BPG but with an increased level of CO₂.

Answer 3

B

Question 4

Which of the following is NOT a transport protein?

A) maltoporin
B) hemoglobin
C) Na⁺ channel
D) DNA polymerase

Question 5

When oxygen binds to hemoglobin,which of the following occurs?

A) The heme group becomes puckered.
B) The atomic radius of the iron is decreased.
C) His F7 is brought closer to the plane of the porphyrin ring.
D) His E8 is brought closer to the plane of the porphyrin ring.

Question 6

Which of the following statements is true for hemoglobin but NOT myoglobin?

A) The tertiary structure is made up of a globin fold.
B) The surface of its tertiary structure contains many hydrophobic amino acids.
C) It contains a proximal histidine that coordinates the heme group.
D) It contains a single carboxyl-terminal amino acid.

Question 7

An effector binds to a single subunit of a multi-subunit allosteric protein.As a result,all subunits switch to the R state.This is an example of the __________ model of allostery.

A) concerted
B) homotropic
C) sequential
D) combined

Question 8

If a metabolic enzyme __________ the energy of activation of a reaction,the rate of product formation will __________.

A) increases; decrease
B) decreases; increase
C) increases; increase
D) decreases; decrease

Question 9

Below is a figure of adult hemoglobin.The arrow points to where __________ binds.

A) glucose
B) 2,3-bisphosphoglycerate
C) O₂
D) CO₂

Question 10

Consider the following interaction between a protein and its ligand: [P] + [L] [PL].
If [L] = 5 mM,[P] = 3 mM,and [PL] = 2 mM,what is the Ka for the interaction?

A) 7.5 mM
B) 15 mM
C) 0.133 mM
D) 0.4 mM

Question 11

Which of the following is true of this compound?

A) It contains a ferric ion.
B) It is a prosthetic group.
C) It is found on the surface of both hemoglobin and myoglobin.
D) It is coordinated to hemoglobin through interactions with a proximal cysteine.

Question 12

Which of the following is NOT a characteristic of an enzyme active site?

A) It has a three-dimensional shape.
B) It plays a role in increasing the energy of activation of the reaction being catalyzed.
C) It is a unique chemical environment.
D) It is where the substrate of the reaction can be found.

Question 13

In both myoglobin and hemoglobin,O₂ reversibly binds to a(n)__________ atom contained in a porphyrin ring that is tightly bound to the protein.

A) calcium
B) iron
C) magnesium
D) manganese

Question 14

The estrogen receptor is a(n)

A) G protein-coupled receptor.
B) receptor tyrosine kinase.
C) nuclear receptor.
D) intracellular signaling protein.

Question 15

Which of the following is a genomic caretaker protein?

A) topoisomerase
B) insulin
C) myoglobin
D) tubulin

Question 16

Nuclear receptors are a type of

A) metabolic enzyme.
B) structural protein.
C) transport protein.
D) cell signaling protein.

Question 17

A reduction in the catalytic ability of carbonic anhydrase may lead to __________ efficient oxygen delivery by hemoglobin as a result of a(n)__________ Bohr effect.

A) less; increased
B) more; increased
C) less; reduced
D) more; reduced

Question 18

Hemoglobin contains __________ -helices,__________
-sheets,and __________ globin folds.

A) 32; 4; 4
B) 32; 0; 8
C) 8; 8; 4
D) 32; 0; 4

Question 19

Which of the following is a positive effector for oxygen binding to hemoglobin?

A) CO₂
B) O₂
C) H⁺
D) 2,3-bisphosphoglycerate

Question 20

Vitamin C is required for prolyl hydroxylase to function.Prolyl hydroxylase enzyme activity is necessary for the proper biosynthesis of collagen.Which of the following might result from a deficiency in vitamin C?

A) higher risk of bone breakage
B) a reduction in muscle contraction ability
C) reduced chromosomal separation during mitosis
D) brittle hair

Question 21

Approximately how many amino acids are identical in both myoglobin and the adult -subunit of hemoglobin?

A) 2%
B) 20%
C) 38%
D) 81%

Question 22

The subunit of adult hemoglobin has higher sequence similarity to __________ than to __________.

A) fetal
Subunit; myoglobin
B) myoglobin; fetal
Subunit
C) adult
1 subunit; fetal
Subunit
D) myoglobin; adult
1 subunit

Question 23

A molecule is found to be able to diffuse across a membrane.Which of the following characteristics would best describe this molecule?

A) hydrophilic
B) hydrophobic
C) neutral
D) polar

Question 24

Consider the following interaction between a protein and its ligand: [P] + [L] [PL].
If [L] = 5 mM,[P] = 3 mM,and [PL] = 2 mM,what is the dissociation constant?

A) 7.5 mM
B) 15 mM
C) 0.133 mM
D) 0.4 mM

Question 25

Look at the data in the figure below.If the sequence for the subunit was replaced with the
Subunit sequence from a patient with sickle cell disease,the number of

A) asterisks would decrease.
B) colons would increase.
C) periods would decrease.
D) asterisks would increase.

Question 26

Consider an allosteric protein that contains three identical subunits.Which of the following is true only if the protein follows the concerted model of allostery and NOT the sequential model of allostery?

A) All three subunits exist in the R state simultaneously.
B) All three subunits exist in the T state simultaneously.
C) A ligand is bound to a single subunit and that subunit is in the T state.
D) No ligand is bound; two subunits are in the T state and one subunit is in the L state.

Question 27

Which of the following is NOT a symptom of anemia?

A) fatigue
B) shortness of breath
C) cognitive decline
D) excessive bleeding

Question 28

A protein that follows the concerted model of allosteric regulation would display a binding curve that is __________.A protein that follows the sequential model of allosteric regulation would display a binding curve that is __________.

A) sigmoidal; hyperbolic
B) hyperbolic; sigmoidal
C) sigmoidal; sigmoidal
D) hyperbolic; hyperbolic

Question 29

The translocation rate of a solute across a membrane is measured.A plot of translocation rate versus solute concentration displays a hyperbolic curve.The translation

A) could be occurring through a passive transport channel.
B) could be occurring by diffusion.
C) could be occurring through a passive transport carrier.
D) must require an input of energy.

Question 30

Using the oxygen binding curve shown,calculate the approximate percentage of O₂ that is released from hemoglobin as the pO₂ changes from 13 kPa to 4 kPa.

A) 4%
B) 9%
C) 60%
D) 91%

Question 31

A mutation of the N-terminal valine in adult hemoglobin occurs.The amino acid is replaced with an isoleucine.Studies show that the replacement does not alter the overall structure of the protein.Which of the following hemoglobin functions may be altered?

A) affinity for 2,3-BPG
B) ability to transport O₂
C) ability to transport CO₂
D) ability to switch from the T state to the R state

Question 32

What type of transport is depicted in the figure below?

A) membrane diffusion
B) passive transport of molecules down a concentration gradient
C) active transport of molecules down a concentration gradient
D) active transport of molecules up a concentration gradient

Question 33

The fractional saturation of hemoglobin (Hb)binding to oxygen is illustrated by

A) [HbO₂] / ([HbO₂] + [Hb]).
B) ([HbO₂] + [Hb]) / [HbO₂].
C) [Hb] / [HbO₂].
D) [HbO₂] / [Hb].

Question 34

The estrogen receptor is an example of a

A) metabolic enzyme.
B) transport protein.
C) genomic caretaker protein.
D) cell signaling protein.

Question 35

Which of the following pairs are paralogous genes?

A) chicken myoglobin; human hemoglobinSubunit
B) chicken hemoglobin Subunit; chicken hemoglobin Subunit
C) human hemoglobin Subunit; chicken hemoglobin Subunit
D) chicken hemoglobin Subunit; human myoglobin

Question 36

Which of the following groups are hydrogen bonded in oxyhemoglobin but not deoxyhemoglobin?

A) Asp94 and Asn102
B) Asp94 and Tyr42
C) Try42 and Asp99
D) Asp99 and Asn102

Question 37

Oxygen binding is monitored for a solution of hemoglobin.During the experiment,the curve changes from sigmoidal to hyperbolic.Which of the following may be the reason for the change?

A) A positive allosteric effector was added.
B) A negative allosteric effector was added.
C) The protein dissociated into individual subunits.
D) The protein denatured.

Question 38

Which of the following may result from a His143 Ala143 mutation in adult hemoglobin?

A) decreased CO₂ transport efficiency
B) increased oxygen transport efficiency
C) reduced affinity for 2,3-BPG
D) sickle cell anemia

Question 39

Which of the following curves is representative of the binding of oxygen to myoglobin?

A) curve A
B) curve B
C) curve C
D) curve D

Question 40

Which of the following is true of sickle cell anemia?

A) It is a dominant genetic disease.
B) It is caused by a mutation in the
-globin gene.
C) It is caused by an amino acid substitution in the F helix.
D) It results in a hemoglobin that contains a hydrophobic amino acid on the surface.

Question 41

Gramicidin A is involved in the __________ transport of __________ charged ions.

A) active; positively
B) active; negatively
C) passive; positively
D) passive; negatively

Question 42

The mutation that would lead to the most dramatic effect on Ca²⁺ transport is a mutation of

A) Ser16 in phospholamban.
B) Thr17 in phospholamban.
C) Asp351 in SERCA.
D) Ser17 in E2P.

Question 43

In studying a transporter,it is found that no external energy input is needed to facilitate the movement of a neutral compound through the transporter.The translocation rate of the compound reaches a plateau at high levels of compound.It is a(n)

A) passive transport channel.
B) passive transport carrier.
C) active transport channel.
D) active transport carrier.

Question 44

Which of the following is NOT an ABC transporter?

A) cystic fibrosis transmembrane conductance regulator protein
B) SERCA
C) multidrug resistance protein
D) maltose transporter from E. coli

Question 45

As K⁺ passes through the selectivity filter of the K⁺ channel of Streptomyces lividans it interacts with

A) glycine side chains.
B) amino acid carbonyl groups.
C) tyrosine side chains.
D) amino acid amino groups.

Question 46

Which is true of the K⁺ channel but NOT of an aquaporin?

A) Selectivity is achieved through interactions with backbone NH groups.
B) It contains -helices.
C) It is an active transporter.
D) Selectivity is assisted through inverted -helix dipoles.

Question 47

Which of the following is a pharmaceutical drug that targets an active transporter?

A) sertraline
B) malate
C) gramicidin A
D) 2,3-BPG

Question 48

Which of the following accounts for some of the specificity of the K⁺ channel?

A) The radius of solvated Na⁺ is smaller than the radius of solvated K⁺.
B) The number of
-strands that make up the channel.
C) The orientation of backbone carbonyl oxygen atoms in the channel.
D) Alternating positive and negative amino acids in the channel pore.

Question 49

Consider the transport scenario shown.Which curve represents the overall movement of the small molecule from the extracellular environment to the cytosol?

A)
B)
C)
D)

Question 50

The selectivity of aquaporin for H₂O relies on all EXCEPT which of the following?

A) hydrogen bonding to Asn
B) a 2.8 Å constriction point within the protein
C) inverted
-helix dipoles
D) electrostatic repulsion from Asn

Question 51

Primary active ABC transporters and P-type transporters both require

A) a conformational change to function.
B) two ATP binding half-sites.
C) solutes that move down their concentration gradients through the transporter.
D) removal of inhibitory subunits to function.

Question 52

A cell with a membrane potential of -70 mV that contains functioning Na⁺-K⁺ ATPase membrane transport proteins will maintain an extracellular __________ concentration that is __________ than the intracellular __________ concentration.

A) Na⁺; lower; K⁺
B) Na⁺; lower; Na⁺
C) K⁺; higher; Na⁺
D) K⁺; lower; K⁺

Question 53

The transport system shown below is a(n)

A) secondary active symporter.
B) primary active transporter.
C) secondary active antiporter.
D) ABC transporter.

Question 54

The E.coli maltoporin protein,but NOT the A.lividans K⁺ channel protein,

A) is a homotetramer.
B) contains mostly -helices.
C) is a passive transporter.
D) uses transport dependent on interaction with amino acid side chains.

Question 55

Passive membrane transporters CANNOT

A) be small peptides.
B) contain
-sheets.
C) contain
-helices.
D) contain only hydrophobic amino acids.

Question 56

As 18 Na⁺ ions are exported out of the cell by the Na⁺-K⁺ ATPase membrane transport protein,__________ K⁺ ions are imported into the cell.

A) 2
B) 12
C) 18
D) 24

Question 57

The lactose permease from E.coli and the molybdate transporter from Archaeoglobus fulgidus both

A) drive transport through the hydrolysis of ATP.
B) drive transport through the use of a concentration gradient.
C) undergo a conformational change that occurs on substrate binding.
D) contain a selectivity filter.

Question 58

Consider a system where a passive transport channel is available for a neutral molecule X.If RTln(C₂/C₁)is zero,then

A) no net transport will occur.
B) the molecule will move from the area where the concentration is C₂ to the area where the concentration is C₁.
C) the molecule will move from the area where the concentration is C₁ to the area where the concentration is C₂.
D) There is no way to determine if or how transport of X will occur given the information provided.

Question 59

What might be the effect on the transport of lactose into the cytosol of E.coli if a drug is added that allows H⁺ to freely pass through the inner bacterial membrane?

A) There would be no effect.
B) Lactose transport would increase.
C) Lactose transport would cease.
D) Lactose would be transported out of the cytosol and into the periplasm.

Question 60

Which of the following is NOT considered part of the thin filament?

A) actin
B) myosin
C) troponin
D) tropomyosin

Question 61

Which of the following statements is true of the data shown below?

A) The binding of ligand to protein B follows the Bohr effect.
B) Both proteins display cooperative binding.
C) Protein A has a higher K_d for the ligand than protein B.
D) Protein B and protein A bind to the same ligand.

Question 62

A myoblast contain(s)__________,but a myofibril does not.

A) actin
B) many nuclei
C) myosin
D) many sarcomeres

Question 63

Consider an oxygen binding curve for hemoglobin at pH 7.4.The binding curve would shift __________ if the pH is reduced to 7.2.

A) to the right
B) to the left
C) up
D) down

Question 64

A newly discovered transporter protein is being investigated using an assay to determine whether transport has occurred in the cells.A nonhydrolyzable form of ATP is added to the cells,and it is found that transport is reduced.Explain these results.

Question 65

Which of the following is NOT a passive transporter protein?

A) porin
B) Cl^- channel
C) Ca²⁺-ATPase transporter protein
D) Ca²⁺ channel

Question 66

Which of the following would shift the oxygen binding curve for hemoglobin to the left?

A) a lower concentration of CO₂
B) a higher pH
C) a higher concentration of 2,3-BPG
D) an increase in the number of hemoglobin molecules in the T state

Question 67

Fetal and adult hemoglobin have different affinities for 2,3-BPG.Predict if O₂ transport from maternal cells to fetal cells will be altered from the normal rate if the
subunit of the fetal red blood cells have a Ser143
His143 mutation.Include the term T state in your answer.

Question 68

A protein displays allosteric regulation.Which of the following is true?

A) Each subunit is either in the T state or the R state, but does not switch from one state to the other.
B) Each subunit can exist in more than one conformation.
C) When the protein binds to a positive allosteric effector, the subunits are more likely to be in the T state.
D) A subunit must be in the R state in order to bind ligand.

Question 69

When ATP binds to myosin,

A) the troponin binding sites are exposed.
B) it cannot interact with actin.
C) the power stroke occurs.
D) the actin nucleotide binding sites are exposed.

Question 70

An oxygen binding curve of fractional saturation versus pO₂ displays a sigmoidal shape.This is the oxygen binding curve for

A) myoglobin.
B) hemoglobin that has been dissociated into individual subunits.
C) hemoglobin in the presence of 2,3-BPG.
D) myoglobin in the presence of 2,3-BPG.

Question 71

A mutation in the subunit of hemoglobin is discovered that reduces the affinity of 2,3-BPG binding.Which of the following mutations is most likely to have this consequence?

A) Val1
Ile1
B) Asp99
Glu99
C) Lys82
Asp82
D) Glu6
Val6

Question 72

Passive transporter proteins allow molecules to move across a membrane in response to

A) chemical gradients.
B) ADP/ATP ratio.
C) ATP/ADP ratio.
D) activated signal transduction pathways.

Question 73

Consider the following interaction between a protein and its ligand: [P] + [L] [PL].
Which equation describes the dissociation constant of this interaction?

A) [PL] / [P][L]
B) [P][L] / [PL]
C) [PL] / [P]
D) [PL][P] / [L]

Question 74

Thin filaments __________,but thick filaments do/are not.

A) contain myosin
B) are directly attached to the Z disk
C) are part of the sarcomere
D) are part of the A band

Question 75

Titin functions to connect __________ to __________.

A) myosin proteins; Z-disk proteins
B) myosin proteins; thin filament proteins
C) actin proteins; Z-disk proteins
D) myosin proteins; tropomyosin

Question 76

Based on the data shown below,the K_d for protein A is __________ the K_d for protein B.

A) equal to
B) approximately 50% greater than
C) six times lower than
D) six times higher than

Question 77

The sarcomere length of isolated heart myoblasts can be measured over time in the laboratory.The myoblasts are maintained in a buffer during the experiment.In a control experiment,Ca²⁺ and ATP are added to the buffer and the change in sarcomere length is analyzed.If EDTA,a chelating agent that sequesters Ca²⁺,was included in the buffer,the length change would be __________ compared with a control experiment without EDTA.

A) smaller
B) greater
C) the same
D) There is no way to determine the result given the information provided.

Question 78

If SERCA is not functioning in a myoblast,which of the following may occur?

A) Myosin will not undergo the conformational change that results in the power stroke.
B) Myosin will not be able to bind to the thin filament.
C) The myofibrils can shorten but not lengthen.
D) The myofibrils can lengthen but not shorten.

Question 79

Which of the following is NOT a definition of fractional saturation for a system of [P] +[L]
[PL]?

A) [PL] / [PL] + [P]
B) [PL] + [P] / [PL]
C) [L] / [L] + K_d
D) occupied binding sites / total binding sites

Question 80

After __________ induced changes in the structure of thin filament,myosin heads containing __________ in the nucleotide binding site will bind with high affinity to actin subunits.

A) ATP; ADP + P_i
B) ATP; Ca²⁺
C) Ca²⁺; ATP
D) Ca²⁺; ADP + P_i