Deck 13: Membrane Channels and Pumps

Question 1

What are passages that exist between adjacent cells that allow movement of ions and small molecules?

A) gap interchanges
B) gap exchanges
C) gap crossings
D) gap inter
E) gap junctions

Answer 1

E

Question 2

In a cell-to-cell junction, 12 molecules of what protein form the gap junction?

A) actin
B) keratin
C) connexin
D) tubulin
E) None of the answers is correct.

Answer 2

C

Question 3

What membrane proteins allow specifically charged species to flow freely across a membrane?

A) aquaporins
B) sodium potassium ATPase
C) glucose transporter
D) ion channels
E) None of the answers is correct.

Answer 3

D

Question 4

Which of the following is a plant extract of steroids used to treat heart failure?

A) digitalis
B) nitroglycerin
C) St. John's wort
D) salicylic acid
E) warfarin

Question 5

What technique is used to measure conductance across a membrane?

A) osmotic flow analysis
B) electron crystallography
C) stop-flow
D) patch-clamp
E) None of the answers is correct.

Question 6

The lactose permease transports lactose into the cell along with a(n) ______________.

Question 7

ABC transporters utilize ____________ to accomplish active transport.

Question 8

Cardiotonic steroids such as digitoxigenin inhibit the _______________________.

Question 9

What amino acid residue receives a phosphoryl group from P-type ATPases?

A) serine
B) tyrosine
C) cysteine
D) lysine
E) aspartate

Question 10

___________________ are an important class of channels that increase the rate at which water flows through membranes.

Question 11

The acetylcholine receptor is an example of a ____________-gated channel.

Question 12

Inorganic ions and most metabolites can flow between the interiors of cells joined by _______________.

Question 13

What is the general term for membrane transporters that couple uphill transport of one species to the downhill flow of another species?

A) cotransporters
B) antiporters
C) symporters
D) uniporters
E) None of the answers is correct.

Question 14

Tetrodotoxin, isolated from puffer fish, binds tightly and specifically to ___________ channels in nerve cells.

Question 15

A P-glycoprotein transporter is also referred to as MDR protein, which is an acronym for _________________________.

Question 16

What family of transport proteins possesses a separate domain or cassette that specifically binds ATP?

A) glucose transporters
B) Na⁺-K⁺ ATPase
C) ABC proteins
D) bicarbonate transporters
E) None of the answers is correct.

Question 17

What type of membrane transporter moves two species in opposite directions across a membrane?

A) symporter
B) antiporter
C) uniporter
D) cotransporter
E) None of the answers is correct.

Question 18

The specific transport of a species down its concentration gradient is referred to as _______________________.

Question 19

Membrane pumps ____________________(consume, produce, or transduce) energy.

Question 20

What is another name for a nerve impulse?

A) action impulse
B) action potential
C) ion potential
D) ion impulse
E) None of the answers is correct.

Question 21

When an uncharged molecule moves from a concentration of 10 ^{- 4} M to 10 ^{- 2} M, is the process spontaneous, at equilibrium, or does it require an input of energy?

A) spontaneous
B) at equilibrium
C) input of energy required
D) It depends on the membrane potential.
E) None of the answers is correct.

Question 22

Ion channels

A) can be selective.
B) exist in open and closed states.
C) in the open state often spontaneously convert into an inactivated state.
D) can be selective and exist in open and closed states.
E) All of the answers are correct.

Question 23

How does the potassium channel maintain selectivity for potassium versus sodium ions?

A) The ion size is the determining factor.
B) The size of the ion and associated waters relative to the pore size are the determining factors in channel selectivity.
C) Dehydration of the potassium ion is compensated energetically by interactions with oxygen atoms in the selectivity filter, which is not possible with sodium ions.
D) Potassium ions associate with six molecules of water while sodium associates with four, thus allowing selectivity.
E) None of the answers is correct.

Question 24

Membrane transporters that couple the downhill flow of one species to the uphill flow of another species in the opposite direction are called

A) antiporters.
B) symporters.
C) exchangers.
D) P-type transporters.
E) None of the answers is correct.

Question 25

What is simple diffusion? Provide an example.

Question 26

Where are gap junctions found?

A) between nerve cells
B) in plasma membranes of apposed cells
C) in the synaptic cleft
D) between the ER and Golgi apparatus
E) None of the answers is correct.

Question 27

Which of the following are true about gap junctions?

A) They are important for intercellular communication.
B) Polar molecules smaller than 1 kDa can pass through them.
C) The channels stay open seconds to minutes.
D) All of the answers are correct.
E) None of the answers is correct.

Question 28

In the potassium ion channel, which of the following is critical in the function of the selectivity filter?

A) The K⁺ binds to a critical Glu residue.
B) The K⁺ binds to the amide groups of three residues in the selectivity filter.
C) The K⁺ binds to the carbonyl groups of the backbone of a conserved pentapeptide sequence.
D) An ATP molecule must be bound for the selectivity filter to operate.
E) None of the answers is correct.

Question 29

As potassium moves through the ion channel, the associated water molecules

A) are shed.
B) remain bound.
C) are rearranged around the ion.
D) react with CO₂.
E) None of the answers is correct.

Question 30

What clues provided evidence of the mechanism of channel inactivation?

A) Trypsin digestion of the cytoplasmic side caused the channel to stay open.
B) Protein mutants have different inactivation kinetics.
C) Inactivation could be restored by the addition of part of a missing peptide.
D) A and B
E) All of the answers are correct.

Question 31

What is the function of selectivity filter amino acids in an ion channel?

A) They close the channel pore after ion passage.
B) They determine the preference for a particular ion.
C) They limit the number of ions passing through the channel.
D) They make sure that only positively charged ions move through the channel
E) None of the answers is correct.

Question 32

Channels that open in response to membrane depolarization are called __________ channels.

A) voltage-gated
B) symport
C) ligand-gated
D) ion-gated
E) None of the answers is correct.

Question 33

How does active transport differ from passive?

Question 34

Which of the following is NOT correct concerning the ABC proteins?

A) They undergo conformational changes upon ATP binding.
B) All are also members of the P-loop NTPase superfamily.
C) The ATP-binding domains are referred to as ATP-binding cassettes.
D) They transfer a phosphate to a conserved Asp residue.
E) They are all true statements.

Question 35

What are the similarities between sodium, potassium, and calcium ion channels?

A) All allow passage of multiple different ions.
B) They contain homologous domains in the membrane spanning regions.
C) They all contain voltage-sensing segments that close the channel in response to a particular membrane potential.
D) They are capable of moving ions in both directions across a membrane.
E) None of the answers is correct.

Question 36

Multidrug resistance in tumor cells is

A) due to the action of a membrane pump that transports small molecules out of the cells.
B) the development of resistance to several drugs following an initial resistance to a single drug.
C) caused by a mutation in the cystic fibrosis gene.
D) due to the action of a membrane pump that transports small molecules out of the cells and the development of resistance to several drugs following an initial resistance to a single drug.
E) All of the answers are correct.

Question 37

A channel that opens in response to binding a particular molecule is called a ________ channel.

A) passive diffusion
B) symport
C) ligand-gated
D) ABC-protein
E) None of the answers is correct.

Question 38

Aquaporins are found in high levels in all of the following tissues except

A) the kidneys.
B) salivary glands.
C) the cornea.
D) red blood cells.
E) the liver.

Question 39

Which of the following is correct concerning the sarcoplasmic reticulum Ca²⁺ ATPase?

A) It is an example of an ABC transporter that interconverts between closed and open forms.
B) It transports Ca²⁺ from the sarcoplasmic reticulum into the cytoplasm.
C) This P-type ATPase maintains a calcium ion concentration of approximately 0.1 $\mu$ M in the cytosol and 1.5 mM in the sarcoplasmic reticulum.
D) One Ca²⁺ is transported for each ATP hydrolyzed.
E) None of the answers is correct.

Question 40

Give the structure of the modified residue that is involved as an intermediate of P-type ATPases.

Question 41

Explain how a voltage-gated channel opens.

Question 42

If the selectivity filter binds the potassium ion tightly, how are ions released to pass through the membrane?

Question 43

How does energy affect the functioning of the Na⁺-K⁺ ATPase?

Question 44

Many pumps are members of the P-type ATPases. If you discovered a new enzyme with similar function, what reaction intermediate would help convince you that your enzyme was a member of this family?

Question 45

What is in the structure of aquaporin that prevents the transport of ions as well as water?

Question 46

Describe the functional domains of the sarcoplasmic reticulum Ca²⁺ ATPase.

Question 47

Describe the acetylcholine receptor shape.

Question 48

Why are gap junctions sealed when high concentrations of calcium ions and protons are present?

Question 49

Since we know that certain amino acids are likely to be found in membranes, why is it so difficult to predict the structure of a channel protein?

Question 50

What is the "ball-and-chain" model?

Question 51

Why is it dangerous to eat puffer fish that are not properly prepared?