Part 2: Questions for 2nd biochem midterm (922 - 987) COPY

Question 1

Which of the following carries the most information on the membrane topology of an ion channel?

Select one:
a. Electronmicroscopic images
b. Evolutionarily conserved sequence motifs
c. The number and composition of subunits
d. Hydropathy plot
e. Molecular weight

Answer 1

d. Hydropathy plot

Question 2

Which of the following statements are true for ion-channel gating?

Select one or more:
a. Gating is a stochastic process
b. Gating is a deterministic process
c. Rate constants describe the probabilities of transition between stable open and closed conformations.
d. Gating schemes describe well the kinetics of ionic currents of the whole cell membrane.
e. Gating schemes are only useful for describing kinetics of single ion channels.

Answer 2

a. Gating is a stochastic process
c. Rate constants describe the probabilities of transition between stable open and closed conformations.
d. Gating schemes describe well the kinetics of ionic currents of the whole cell membrane.

Question 3

What is the definition of open probability of an ion channel?

Select one:
a. The total time spent in the open state divided by the total time spent in the closed state.
b. The total time spent in the open state divided by the total observation time. c. The probability that a closed channel will open within a unit time.
d. The probability that an open channel will close within unit time.
e. The probability that ionic current can flow through an open channel.

Answer 3

b. The total time spent in the open state divided by the total observation time.

Question 4

Which statements are true for the throughput rates of open ion channels?

A: Under physiological ion concentrations they approach the theoretical upper limit.
B: Typical throughput rates are 10^3 - 10^4 ions/second.
C: Typical throughput rates are 10^7 - 10^8 ions/second.
D: Typical throughput rates are 10^10 - 10^11 ions/second.
E: The throughput rate can be saturated at high ionic concentrations.

Answer 4

A: Under physiological ion concentrations they approach the theoretical upper limit.
C: Typical throughput rates are 10^7 - 10^8 ions/second.
E: The throughput rate can be saturated at high ionic concentrations.

Question 5

How can we explain the saturation of ion-channel throughput rates at high ion concentrations?

Select one:
a. By an active transport mechanism.
b. At high ion concentrations the throughput rate becomes diffusion limited.
c. By passive diffusion through a cylindrical hole.
d. The pore contains binding sites for the permeant ion; at high ion concentrations the off-rate of the ion from its binding site becomes rate limiting.
e. None of the above provides an explanation.

Answer 5

d. The pore contains binding sites for the permeant ion; at high ion concentrations the off-rate of the ion from its binding site becomes rate limiting.

Question 6

What is true for the selectivity of ion channels?

Select one or more:
a. They can discriminate even between identically charged ions
b. They can only discriminate cations from anions
c. In Ca2+-free media Ca2+ channels become permeable for Na+
d. Conserved P-loop sequences determine selectivity of K+, Na+, and Ca2+ channels
e. Some ion channels are non-selective

Answer 6

a. They can discriminate even between identically charged ions
c. In Ca2+-free media Ca2+ channels become permeable for Na+
d. Conserved P-loop sequences determine selectivity of K+, Na+, and Ca2+ channels
e. Some ion channels are non-selective

Question 7

What is true for the subunit composition of most K+ channels?

Select one:
a. They are monomers
b. They are dimers
c. They are trimers
d. They are tetramers
e. They are pentamers

Answer 7

They are tetramers

Question 8

Which statements is true concerning the structure of the K+ channel?

Select one or more:
a. 4-fold rotational symmetry
b. 5-fold rotational symmetry
c. The selectivity filter is located close to the extracellular, the gate close to the intracellular side
d. The selectivity filter is located close to the intracellular, the gate close to the extracellular side
e. The central cavity communicates with the extracellular solution through the gate

Answer 8

a. 4-fold rotational symmetry
c. The selectivity filter is located close to the extracellular, the gate close to the intracellular side

Question 9

What is the chemical basis for K+-Na+ selection in the selectivity filter of a K+ channel?

Select one:
a. Na+ has a larger hydration shell than K+, therefore Na+ cannot fit through the narrow filter.
b. Na+ is larger in diameter than K+, therefore Na+ cannot fit through the narrow filter.
c. Na+ cannot pass through the intracellular gate.
d. K+ and Na+ could both pass through the filter, but intracellular [K+] is higher.
e. Carbonyl oxygens of the conserved selectivity filter mimic the geometry of the K+ ion

Answer 9

e. Carbonyl oxygens of the conserved selectivity filter mimic the geometry of the K+ ion

Question 10

The movement of how many unitary charges precede activation of a voltage- gated K+ channel?
Select one:
a. 0.1-0.2
b. 1-2
c. 4-6
d. 12-16
e. 40-60

Answer 10

d. 12-16

Question 11

What provides the gating charge of voltage-gated K+, Na+ and Ca2+ channels?

Select one:
a. Positive charges of lysine and arginine side chains
b. Negative charges of lysine and arginine side chains
c. Positive charges of aspartate and glutamate side chains
d. Negative charges of aspartate and glutamate side chains
e. Positive charges of the permeant cations

Answer 11

a. Positive charges of lysine and arginine side chains

Question 12

What is the mechanism of N-type inactivation of voltage-gated K+ channels?

Select one:
a. The N-terminus of the channel polypeptide is enzymatically cleaved off. b. The N-terminus of the channel polypeptide plugs the pore from the extracellular side.
c. The C-terminus of the channel polypeptide plugs the pore from the intracellular side.
d. The C-terminus of the channel polypeptide plugs the pore from the extracellular side.
e. The N-terminus of the channel polypeptide plugs the pore from the intracellular side.

Answer 12

e. The N-terminus of the channel polypeptide plugs the pore from the intracellular side.

Question 13

Which structural motif binds activating Ca2+ ions in Ca2+-activated K+ channels?

Select one:
a. The gating ring which consists of the channels extracellular RCK domains. b. The gating ring which consists of the channels intracellular RCK domains. c. Binding sites located in the central cavity.
d. The selectivity filter which is formed by the conserved P-loops.
e. The gate on the intracellular side (“smoke-hole”).

Answer 13

b. The gating ring which consists of the channels intracellular RCK domains.

Question 14

What is the subunit composition of ATP-sensitive K+ channels?

Select one:
a. Octamer of 4 inward rectifier K+ channel subunits and 4 sulfonylurea receptor subunits
b. Tetramer of 4 inward rectifier K+ channel subunits
c. Tetramer of 4 sulfonylurea receptor subunits
d. Two-pore dimer formed from two polypeptide chains
e. Monomer

Answer 14

a. Octamer of 4 inward rectifier K+ channel subunits and 4 sulfonylurea receptor subunits

Question 15

What is true for the gating of ATP-sensitive K+ channels?

Select one or more:
a. Intracellular ATP inhibits, intracellular ADP activates.
b. Intracellular ADP inhibits, intracellular ATP activates.
c. Intracellular ATP inhibits, extracellular ATP activates.
d. Sulfonylureas inhibit by binding to the extracellular ligand binding site of the sulfonylurea receptor.
e. Sulfonylureas inhibit by binding to the intracellular nucleotide binding domains of the sulfonylurea receptor.

Answer 15

a. Intracellular ATP inhibits, intracellular ADP activates.
e. Sulfonylureas inhibit by binding to the intracellular nucleotide binding domains of the sulfonylurea receptor.

Question 16

What is true for the subunit composition of voltage-gated Cl- channels?

Select one:
a. Two-pore dimers, both polypeptide chains contribute to forming both pores.
b. Two-pore dimers, each polypeptide chain individually forms a pore.
c. Single-pore dimers, both polypeptide chains contribute to forming the pore.
d. Single-pore tetramers
e. Single-pore monomers

Answer 16

b. Two-pore dimers, each polypeptide chain individually forms a pore.

Question 17

Which disease can be the consequence of mutations of the voltage-gated Cl- channel Clc-1?

Select one:
a. Epilepsy
b. Myasthenia
c. Cystic fibrosis
d. Myotonia
e. Long QT syndrome

Answer 17

d. Myotonia

Question 18

Which statements are true concerning the CFTR Cl- channels?

Select one or more:
a. It is activated by cAMP-dependent protein kinase.
b. It is activated by elevations of intracellular [Ca2+].
c. The channel is a receptor tyrosine-kinase which activates upon autophosphorylation.
d. Mutations of the channel can cause cystic fibrosis.
e. The channel is gated by two intracellular nucleotide binding domains which hydrolyze ATP.

Answer 18

a. It is activated by cAMP-dependent protein kinase.
d. Mutations of the channel can cause cystic fibrosis.
e. The channel is gated by two intracellular nucleotide binding domains which hydrolyze ATP.

Question 19

Which statements are true concerning the nicotinic acetylcholine receptor channel?

Select one or more:
a. The channel is a homopentamer, its dysfunction can lead to myasthenia.
b. The channel is a heteropentamer, its dysfunction can lead to myasthenia.
c. The channel is a tetramer, its dysfunction can lead to myotonia.
d. The ligand binding domain is a 4-fold symmetrical gating ring.
e. The ligand binding domain is a 5-fold symmetrical ring.

Answer 19

b. The channel is a heteropentamer, its dysfunction can lead to myasthenia.
e. The ligand binding domain is a 5-fold symmetrical ring.

Question 20

What is the basis of time-dependent changes in membrane permeability?

Select one:
a. Opening of discrete protein pores
b. Changes in the lipid composition of the membrane
c. Changes in ion concentrations
d. Changes in electrical conductivity of the lipid bilayer
e. None of the above

Answer 20

a. Opening of discrete protein pores

Question 21

Which technique is most suitable for studying the gating of individual ion channels?

Select one:
a. The patch-clamp technique
b. Aminoacid sequence analysis.
c. Construction of hydropathy plots.
d. X-ray crystallography.
e. Electron microscopy.

Answer 21

a. The patch-clamp technique

Question 22

Which of the following carries the most information on the membrane topology of an ion channel?

Select one:
a. Hydropathy plot
b. Evolutionarily conserved sequence motifs
c. The number and composition of subunits
d. Electronmicroscopic images
e. Molecular weight

Answer 22

a. Hydropathy plot

Question 23

Which parameter of the nicotinic acetylcholine receptor channel changes upon exposure to acetylcholine?

Select one:
a. Open probability
b. Single-channel conductance.
c. The number of channels in the membrane.
d. The extracellular chloride concentration.
e. The intracellular chloride concentration.

Answer 23

e. The intracellular chloride concentration.

Question 24

Which parameter of the voltage-gated Na+ channel changes upon membrane depolarization?

Select one:
a. The number of channels in the membrane. b. The intracellular chloride concentration.
c. The extracellular chloride concentration.
d. Single-channel conductance.
e. Open probability

Answer 24

e. Open probability

Question 25

Which of the following statements are true for ion-channel gating?

Select one or more:
a. Gating is a stochastic process
b. Gating is a deterministic process
c. Rate constants describe the probabilities of transition between stable open and closed conformations.
d. Gating schemes describe well the kinetics of ionic currents of the whole cell membrane.
e. Gating schemes are only useful for describing kinetics of single ion channels.

Answer 25

a. Gating is a stochastic process
c. Rate constants describe the probabilities of transition between stable open and closed conformations.
e. Gating schemes are only useful for describing kinetics of single ion channels.

Question 26

Which of the following is true?

Select one or more:
a. Changes in the conductance of individual ion channels is the major cause of changes in membrane ion permeability.
b. Changes in the open probability of individual ion channels is the major cause of changes in membrane ion permeability.
c. Repeated exposures of a single ion channel to a ligand evoke always exactly the same response.
d. Exposure of a single ion channel to a ligand may affect the rate constants of gating.
e. Exposure of a single ion channel to a ligand may affect the open probability.

Answer 26

b. Changes in the open probability of individual ion channels is the major cause of changes in membrane ion permeability
d. Exposure of a single ion channel to a ligand may affect the rate constants of gating.
e. Exposure of a single ion channel to a ligand may affect the open probability.

Question 27

What is the definition of open probability of an ion channel?

Select one:
a. The probability that a closed channel will open within a unit time.
b. The total time spent in the open state divided by the total time spent in the closed state.
c. The total time spent in the open state divided by the total observation time.
d. The probability that an open channel will close within unit time.
e. The probability that ionic current can flow through an open channel.

Answer 27

c. The total time spent in the open state divided by the total observation time.

Question 28

Which of the following is true?

Select one or more:
a. Membrane depolarization increases the conductance of individual voltage- gated ion channels.
b. Membrane depolarization increases the open probability of individual voltage-gated ion channels.
c. Repeated depolarizations evoke always exactly the same response of a single ion channel.
d. Depolarization may affect the rate constants of gating of a single ion channel.
e. Depolarization may affect the open probability of a single ion channel.

Answer 28

b. Membrane depolarization increases the open probability of individual voltage-gated ion channels.
d. Depolarization may affect the rate constants of gating of a single ion channel.
e. Depolarization may affect the open probability of a single ion channel.

Question 29

Which statements are true for the throughput rates of open ion channels?

Select one or more:
a. Under physiological ion concentrations they approach the theoretical upper limit.
b. Typical throughput rates are 103-104 ions/second
c. Typical throughput rates are 107-108 ions/second
d. Typical throughput rates are 1010-1011 ions/second
e. The througput rate can be saturated at high ionic concentrations.

Answer 29

a. Under physiological ion concentrations they approach the theoretical upper limit.
c. Typical throughput rates are 107-108 ions/second (Not sure about this -> check the textbook again)
e. The througput rate can be saturated at high ionic concentrations.

Question 30

How can we explain the saturation of ion-channel throughput rates at high ion concentrations?

Select one:
a. At high ion concentrations the throughput rate becomes diffusion limited.
b. By passive diffusion through a cylindrical hole.
c. By an active transport mechanism.
d. The pore contains binding sites for the permeant ion; at high ion concentrations the off-rate of the ion from its binding site becomes rate limiting.
e. None of the above provides an explanation.

Answer 30

d. The pore contains binding sites for the permeant ion; at high ion concentrations the off-rate of the ion from its binding site becomes rate limiting.

Question 31

What is true for the selectivity of ion channels?

Select one:
a. The structural basis for K+ channel selectivity is provided by the voltage sensor paddle.
b. The structural basis for Na+ channel selectivity is provided by the voltage sensor paddle.
c. The structural basis for K+ channel selectivity is provided by the P-loop.
d. The structural basis for Cl- channel selectivity is provided by the P-loop.
e. Inward rectifier K+ channels do not have a P-loop

Answer 31

c. The structural basis for K+ channel selectivity is provided by the P-loop.

Question 32

What is true for the selectivity filter of voltage-gated cation channels?

Select one:
a. Only one cation can be found in the filter at any time.
b. One or more cations can be found in the filter at the same time.
c. One cation and one anion can be found in the filter at any time.
d. Anions are excluded from the filter, because they are too large.
e. Anions are excluded from the filter, because they are too small.

Answer 32

b. One or more cations can be found in the filter at the same time.

Question 33

What is true for the selectivity of ion channels?

Select one or more:
a. They can discriminate even between identically charged ions
b. They can only discriminate cations from anions
c. In Ca2+-free media Ca2+ channels become permeable for Na+
d. Conserved P-loop sequences determine selectivity of K+, Na+, and Ca2+ channels
e. Some ion channels are non-selective

Answer 33

a. They can discriminate even between identically charged ions
c. In Ca2+-free media Ca2+ channels become permeable for Na+
d. Conserved P-loop sequences determine selectivity of K+, Na+, and Ca2+ channels
e. Some ion channels are non-selective

Question 34

What is true for the subunit composition of most K+ channels?

Select one:
a. They are tetramers
b. They are monomers
c. They are dimers
d. They are trimers
e. They are pentamers

Answer 34

a. They are tetramers

Question 35

Which statements are true concerning the structure of the K+ channel?

Select one or more:
a. 4-fold rotational symmetry
b. 5-fold rotational symmetry
c. The selectivity filter is located close to the extracellular, the gate close to the intracellular side
d. The selectivity filter is located close to the intracellular, the gate close to the extraracellular side
e. The central cavity communicates with the extracellular solution through the gate

Answer 35

a. 4-fold rotational symmetry
c. The selectivity filter is located close to the extracellular, the gate close to the intracellular side

Question 36

What is true for the architecture of K+ channels?
Select one:
a. The selectivity filter is on the extracellular, the gate is on the intracellular side.
b. The selectivity filter is on the intracellular, the gate is on the intracellular side.
c. The selectivity filter is on the extracellular, the gate is on the extracellular side.
d. The selectivity filter is on the intracellular, the gate is on the extracellular side.
e. None of the above.

Answer 36

a. The selectivity filter is on the extracellular, the gate is on the intracellular side.

Question 37

What chemical groups provide the ion binding sites in the selectivity filter of K+ channels?

Select one:
a. Carbonyl oxygens of the peptide backbone
b. Aromatic rings of tyrosine sidechains.
c. Carboxylate groups of aspartate sidechains.
d. Carboxylate groups of glutamate sidechains.
e. None of the above.

Answer 37

a. Carbonyl oxygens of the peptide backbone

Question 38

What is the chemical basis for K+-Na+ selection in the selectivity filter of a K+ channel?

Select one:
a. Carbonyl oxygens of the conserved selectivity filter mimic the geometry of the K+ ion hydration shell, but are too far apart for optimal coordination of Na+.
b. Na+ is larger in diameter than K+, therefore Na+ cannot fit through the narrow filter.
c. Na+ cannot pass through the intracellular gate.
d. K+ and Na+ could both pass through the filter, but intracellular [K+] is higher.
e. Na+ has a larger hydration shell than K+, therefore Na+ cannot fit through the narrow filter.

Answer 38

a. Carbonyl oxygens of the conserved selectivity filter mimic the geometry of the K+ ion hydration shell, but are too far apart for optimal coordination of Na+.

Question 39

Which parts of the fibrinogen polypeptide chains are located in the central domain of the molecule?

Select one:
a. α C-terminal
b. β C-terminal
c. γ C-terminal
d. the C-terminals of all three chains

Answer 39

a. α C-terminal

Question 40

Which serum biomarker is a direct indicator of in vivo thrombin activity?

Select one:
a. meizothrombin
b. fibrinopeptide A
c. fragment 1,2
d. fibrin monomer

Answer 40

b. fibrinopeptide A

Question 41

What is true concerning fibrinogen-γ’?

Select one:
a. it comprises 50 % of normal fibrinogen
b. its elevated level in blood predisposes to bleeding
c. its elevated level in blood predisposes to arterial thrombosis
d. its elevated level in blood predisposes to venous thrombosis

Answer 41

c. its elevated level in blood predisposes to arterial thrombosis

Question 42

Which cofactor icreases the affinity of thrombin to plasma FXIII?

Select one:
a. tissue factor
b. fibrin
c. FVa
d. Phospholipid

Answer 42

b. fibrin

Question 43

What is inhibited by TFPI (tissue factor pathway inhibitor)?

Select one:
a. tissue factor
b. prothrombinase
c. thrombin
d. FVa

Answer 43

b. prothrombinase

Question 44

Which inhibitor can inhibit the target proteases of blood coagulation when they are bound to membrane?

Select one:
a. TFPI (tissue factor pathway inhibitor)
b. antithrombin
c. α1-protease inhibitor
d. α2-macroglobulin

Answer 44

d. it is less susceptible to non-specific interactions in vivo

Question 45

What is true concerning the mechanism of action of α2-macroglobulin?

Select one:
a. it forms an ester bond with the protease
b. it forms an isopeptide bond with the protease
c. it acts as any other serpin
d. it forms a non-covalent complex with the protease

Answer 45

b. it forms an isopeptide bond with the protease

Question 46

What does γ-carboxyglutamate bind?
Select one:

a. Ca2+
b. Phospholipid
c. FVa
d. FVIIIa

Answer 46

a. Ca2+

Question 47

Which protein contains a Gla-domain?
Select one:
a. Thrombin
b. FVa
c. FVIIIa
d. FXa

Answer 47

d. FXa

Question 48

What is inhibited by coumarins?

Select one:
a. thrombin
b. γ-Glutamate carboxylase
c. vitamin K-oxidoreductase
d. platelet activation

Answer 48

c. vitamin K-oxidoreductase

Question 49

What is true about the function of FXII?

Select one:
a. it iit triggers blood clotting at sites of injury
b. it amplifies the tissue factor activity
c. its inhibition reduces the size of thrombi
d. it is activated by thrombin in a positive regulatory feed-back loop

Answer 49

c. its inhibition reduces the size of thrombi

Question 50

Which protein is an equally good substrate for both meizothrombin and thrombin?

Select one:
a. protein C
b. fibrinogen
c. factor V
d. antithrombin

Answer 50

a. protein C

Question 51

What kind of abnormality is the most common cause of APC (activated protein C) resistance?

Select one:
a. protein C mutation
b. protein S mutation
c. factor V mutation
d. antithrombin mutation

Answer 51

c. factor V mutation

Question 52

What are the clinical consequences of APC (activated protein C) resistance?

Select one:
a. venous thrombosis
b. arterial thrombosis
c. gastrointestinal bleeding
d. both venous and arterial thrombosis

Answer 52

a. venous thrombosis

Question 53

The activity of which factor is enhanced in APC (activated protein C) resistance?

Select one:
a. prothrombin
b. activated protein C
c. factor VIIIa
d. tissue factor

Answer 53

c. factor VIIIa

Question 54

How is the activated partial thromboplastin time changed in APC (activated protein C) resistance?

Select one:
a. prolonged
b. shortened
c. normal
d. prolonged in acquired and shortened in inherited forms

Answer 54

c. normal

Question 55

What is the effect of activated protein C addition on the APTT (activated partial thromboplastin time) of normal plasma?

Select one:
a. prolongation
b. shortening
c. no effect
d. shortening if thrombomodulin is also added

Answer 55

a. prolongation

Question 56

Which agent should be used at first to treat an acute episode of thrombosis in APC (activated protein C) resistance?

Select one:
a. vitamin K antagonist
b. anti-platelet agent
c. heparin
d. antithrombin

Answer 56

c. heparin

Question 57

How long should a patient with homozygous FV Leiden mutation be anticoagulated?

Select one:
a. 1 month after diagnosis
b. 6 months after diagnosis
c. 1 year after diagnosis
d. life-long

Answer 57

d. life-long

Question 58

Which effect is relevant concerning the prothrombotic effects of hormonal oral contraceptives?

Select one:
a. decreased TFPI (tissue factor pathway inhibitor) level in blood
b. decreased FII level in blood
c. increased TFPI (tissue factor pathway inhibitor) level in blood
d. decreased FVIII level in blood

Answer 58

d. TFPI (tissue factor pathway inhibitor)+FIIa

Question 59

In which vessels are thrombi observed in antiphospholipid syndrome?

Select one:
a. arteries only
b. veins only
c. both arteries and veins
d. capillaries only

Answer 59

c. both arteries and veins

Question 60

What is a typical laboratory finding in antiphospholipid syndrome?

Select one:
a. shortened activate partial thromboplastin time (APTT)
b. prolonged activated partial thromboplastin time (APTT)
c. prolonged activated partial thromboplastin time (APTT) only after treatment of the plasma with platelet membrane
d. prolonged activated partial thromboplastin time (APTT) only after treatment of the plasma with protein C

Answer 60

b. prolonged activated partial thromboplastin time (APTT)

Question 61

What is true concerning β2-glycoprotein I?

Select one:
a. it is an immunoglobulin
b. it is a thrombin inhibitor
c. it scavenges apoptotic membranes
d. it is a product of platelets

Answer 61

c. it scavenges apoptotic membranes

Question 62

Which one is recommended as a therapeutic agent in a pregnant patient with antiphospholipid syndrome (APS)?

Select one:
a. heparin
b. warfarin
c. activated protein S
d. β2-glycoprotein I

Answer 62

a. heparin

Question 63

The proton motive force is the sum of:

Select one:
a. Proton gradient and electrical potential difference across the outer mitochondrial membrane
b. Proton gradient and ATP gradient across the outer mitochondrial membrane
c. Proton gradient and electrical potential difference across the inner mitochondrial membrane
d. Proton gradient and ATP gradient across the inner mitochondrial membrane
e. Electrical potential difference and ATP gradient across the inner mitochondrial membrane

Answer 63

c. Proton gradient and electrical potential difference across the inner mitochondrial membrane