Chapter 11: Assignment Questions COMPLETE

Question 1

For a typical mammalian cell, [Na+] is higher:

in the extracellular space
in the cyotsol

Answer 1

in the extracellular space

Question 2

For a typical mammalian cell, [K+] is higher:

in the extracellular fluid
in the cytosol

Answer 2

in the cytosol

Question 3

For a typical mammalian cell, [Ca2+] is about 10,000-20,000 times higher _______ than in the other choice below.

in the extracellular fluid
in the cytosol

Answer 3

in the extracellular fluid

Question 4

For a typical mammalian cell, pH is a bit higher (7.4 vs 7.2)

in the extracellular fluid
in the cytosol

Answer 4

in the extracellular fluid

Question 5

Which can most readily cross a lipid bilayer?

non-polar molecules such as O2, CO2, steroid hormones, etc.
small, uncharged polar molecules such as H2O
large, uncharged polar molecules such as glucose
ions such as H+, Na+, K+, Ca2+, etc.

Answer 5

non-polar molecules such as O2, CO2, steroid hormones, etc.

Question 6

Which can least readily cross a lipid bilayer?

non-polar molecules such as O2, CO2, steroid hormones, etc.
small, uncharged polar molecules such as H2O
large, uncharged polar molecules such as glucose
ions such as H+, Na+, K+, Ca2+, etc.

Answer 6

ions such as H+, Na+, K+, Ca2+, etc.

Question 7

The limiting factor of simple diffusion of a molecule across a lipid bilayer is:

ability to interact with polar head groups of the membrane lipids
ability to interact with the hydrophobic interior of the lipid bilayer

Answer 7

ability to interact with the hydrophobic interior of the lipid bilayer

Question 8

Which of these groups is hydrophobic?

-OH
-COO-
Correct!
-CH3
-H3N+

Answer 8

-CH3

Question 9

Given that the direction of net movement of the solutes always down its concentration gradient, which way can the solute move?

into the cell
out of the cell
either in or out, depending on the concentration gradient

Answer 9

either in or out, depending on the concentration gradient

Question 10

The kind of transporter/carrier- or channel-mediated movement that goes in the direction of the concentration gradient (from high to low) is called:

passive transport
secondary active transport
active transport

Answer 10

passive transport

Question 11

Sometimes, a molecule has both a chemical gradient and an electrical (charge) gradient. That’s the:

chemical gradient
electrical gradient
voltage gradient
electrochemical gradient

Answer 11

electrochemical gradient

Question 12

Which protein mediates active transport?

simple diffusion
channel-mediated
transporter mediated
active transport

Answer 12

active transport

Question 13

Simple diffusion is:

active transport
movement against a concentration gradient
channel-mediated
transporter/carrier mediated
direct diffusion of a molecule across a lipid bilayer without involvement of a membrane protein

Answer 13

direct diffusion of a molecule across a lipid bilayer without involvement of a membrane protein

Question 14

A researcher does an experiment that involves measuring rate of movement of a solute across a lipid bilayer. In the case of a certain solute, the movement rate keeps going up as the solute concentration increases and is never saturated (i.e. never reaches a point at which movement no longer increases even when solute concentration increases). This type of movement could be:

simple diffusion or channel mediated transport
carrier/transporter mediated facilitated diffusion
active transport

Answer 14

simple diffusion or channel mediated transport

Question 15

When a protein couples ATP hydrolysis with “pumping” a solute across a lipid bilayer to create a chemical or electrochemical gradient for that solute, and then movement of that solute back across the lipid bilayer down its gradient drives movement of another solute, that’s:

secondary active transport
simple diffusion
facilitated diffusion

Answer 15

secondary active transport

Question 16

A common feature of (coupled transporter, ATP-driven pump, light0driven pump) means of active transport is that:

they are coupled to some source of potential energy (e.g. light, chemical energy in bonds of ATP, potential energy of an electrochemical gradient)
they mediate simple diffusion
they mediate facilitated diffusion

Answer 16

they are coupled to some source of potential energy (e.g. light, chemical energy in bonds of ATP, potential energy of an electrochemical gradient)

Question 17

a uniporter carries:

a molecule and ion in the same
a molecule and ion in different directions
a molecule one direction

Answer 17

a molecule one direction

Question 18

an antiporter carries:

a molecule and ion in the same
a molecule and ion in different directions
a molecule one direction

Answer 18

a molecule and ion in different directions

Question 19

a symporter carries:

a molecule and ion in the same
a molecule and ion in different directions
a molecule one direction

Answer 19

a molecule and ion in the same

Question 20

In some tissues, a Na+/K+ pump creates a sodium gradient that then drives glucose uptake by the sodium-dependent glucose transporter. That’s an example of:

secondary active transport
facilitated diffusion
simple diffusion

Answer 20

secondary active transport

Question 21

In other cases, there’s no need for active transport to create a sodium gradient, such as in the small intestine after ingestion of foods or beverages containing sodium. What would you say to that?

Neat!
impossible!

Answer 21

Neat!

Question 22

The pH of a cell or subcellular compartment can be regulated by:

transport of H+ across a membrane by a proton pump or a Na+/H+ exchanger
movement of bicarbonate (HCO3-) across a membrane, such as by a chloride/bicarbonate exchanger
both are common mechanisms for regulation of pH!

Answer 22

both are common mechanisms for regulation of pH!

Question 23

The carbonic anhydrase reaction is a key regulator of pH because:

The reaction it catalyzes (HCO3– + H+ ⇓⋄ H2O + CO2 ) can produce or consume protons, depending on the relative concentrations of the substrates/products
carbonic anhydrase is a proton pump

Answer 23

The reaction it catalyzes (HCO3– + H+ ⇓⋄ H2O + CO2 ) can produce or consume protons, depending on the relative concentrations of the substrates/products

Question 24

On which side of the epithelial cell is glucose transport sodium dependent?

on the apical or brush-border side (facing the lumen of the small intestine, top of figure)
on the basolateral side (facing the extracellular fluid near the capillaries, bottom of figure)

Answer 24

on the apical or brush-border side (facing the lumen of the small intestine, top of figure)

Question 25

On which side of the epithelial cell is glucose transport mediated by facilitated diffusion?

on the apical or brush-border side (facing the lumen of the small intestine, top of figure)
on the basolateral side (facing the extracellular fluid near the capillaries, bottom of figure)

Answer 25

on the basolateral side (facing the extracellular fluid near the capillaries, bottom of figure)

Question 26

Which of these ion pumps is essentially like the mitochondrial or chloroplast F-type ATP synthase except running in reverse?

P-type pump
ABC transporter
V-type (Vacuolar, vesicular, lysosomal, etc.) proton pump

Answer 26

V-type (Vacuolar, vesicular, lysosomal, etc.) proton pump

Question 27

The pump that moves Ca2+ from the cytosol into the endoplasmic reticulum or sarcoplasmic reticulum (the SR/ER calcium ATPase, or SERCA) is phosphorylated during its pumping cycle and is classified as:

a P-type pump
an ABC transporter
a V-type H+ pump
an F-type ATP synthase

Answer 27

a P-type pump

Question 28

Action of the Na+/K+
ATPase makes the cytosol more __________ than the extracellular fluid.

negative
positive

Answer 28

negative

Question 29

When a protein couples ATP hydrolysis with “pumping” a solute across a lipid bilayer against its gradient, that’s:

simple diffusion
facilitated diffusion
active transport

Answer 29

active transport

Question 30

A multidrug resistance protein that can couple ATP hydrolysis to pumping of hydrophobic molecules, including some cancer chemotherapy drugs, out of the cytosol is:

a P-type pump
an ABC transporter
a V-type H+ pump
an F-type ATP synthase

Answer 30

an ABC transporter

Question 31

The cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ABC transporter family that does not function in the normal ABC fashion. Instead of pumping, it mediates conduction of anions down their electrochemical gradients. Given the distribution of charge inside and outside of typical mammalian cells, which way would Cl-
move through CFTR? For reference, resting membrane potential (e.g. around -70 or -80 mV) is generally more negative than the equilibrium potential of Cl- (e.g. around -60 mV).

out of a cell
into the cytosol

Answer 31

out of a cell

Question 32

Movement of water across a membrane occurs at a greater rate:

by simple diffusion
by movement through aquaporins

Answer 32

by movement through aquaporins

Question 33

Either way, by simple diffusion or through aquaporins, net water movement is from an area with _______ solute concentration toward an area with ___________ solute concentration.

higher; lower
lower; higher

Answer 33

lower; higher

Question 34

In a gland containing aqua porins, which occurs first?

conduction of ions (e.g. Na+, Cl-, etc.) through the cells into the fluid-filled structure of this gland

movement of water, mostly mediated by aquaporins, through the cells and into the fluid-filled structure of this gland

Answer 34

conduction of ions (e.g. Na+, Cl-, etc.) through the cells into the fluid-filled structure of this gland

Question 35

The partial _______ charges of the hydrogen atoms on the two asparagine side chains in the center of this aquaporin attract the _______ of a water molecule.

positive; oxygen atom
negative; oxygen atom
positive; hydrogen atoms
negative; hydrogen atoms

Answer 35

positive; oxygen atom

Question 36

The oxygen atoms of the carbonyl groups lining the aquaporin channel attract:

the partial positive charges of hydrogen atoms in water

the partial negative charges of oxygen atoms in water

Answer 36

the partial positive charges of hydrogen atoms in water

Question 37

Given all of that alignment of water molecules in the aquaporin channel by carbonyl groups and the asparagines, are there any availalbe hydrogen-bonding partners on water molecules for H+ ions to get through the channel?

nope, nope, and nope
yes?

Answer 37

nope, nope, and nope

Question 38

A subset of plasma membrane K+ channels, known as K+ leak channels, are open even in unstimulated conditions. These channels allow K+ to:

move down its concentration gradient out of a cell until the electrical gradient attracting K+ into the cell balances the tendency of K+ to move out of the cell down its chemical gradient

pump K+ into a cell

Answer 38

move down its concentration gradient out of a cell until the electrical gradient attracting K+ into the cell balances the tendency of K+ to move out of the cell down its chemical gradient

Question 39

At resting potential of a mammalian cell:

the interior of the cell, especially the area near the plasma membrane, has more negative charge than the exterior

the exterior of the cell has relatively greater positive charge than the interior

both!

Answer 39

both!

Question 40

Would it be likely that the carbonyl-lined pore of this channel would allow passage of anions?

no
yes

Answer 40

no

Question 41

Alpha helices have a dipole, such that there is a charge gradient from a partial negative charge at the carboxy end toward a partial positive at the amino end. If alpha helices help attract a K+
ion to the channel pore entrance, which helix ends likely face the entrance of the pore?

carboxy end
N-terminal end

Answer 41

carboxy end

Question 42

This model of the selectivity filter of a potassium channel shows that the basis of selectivity is:

the partial charges lining the filter
the spacing between the peptides lining the filter

Answer 42

the spacing between the peptides lining the filter

Question 43

Voltage-gated Na+ channels open in response to:

depolarization (the membrane potential becoming less negative)

polarization (the membrane potential becoming more negative)

Answer 43

depolarization (the membrane potential becoming less negative)

Question 44

Which could cause depolarization?

Na+ entering a cell
Cl- entering a cell
K+ leaving a cell

Answer 44

Na+ entering a cell

Question 45

In certain cell types (not neurons or skeletal muscle), the primary means of depolarization is:

Ca2+ entering a cell
Cl- entering a cell
K+ leaving a cell

Answer 45

Ca2+ entering a cell

Question 46

Opening of voltage-gated K+
channels leads to:

polarization
depolarization

Answer 46

polarization

Question 47

The voltage-sensitive helices of a voltage-gated ion channel have abundant positively charged side chains that are attracted toward the relatively negatively-charged cytosol. When a membrane depolarization occurs, there’s relatively less charge gradient across the membrane, so the helices move:

toward the extracellular direction, because there’s relatively less charge attraction from within

toward the cytosolic direction

Answer 47

toward the extracellular direction, because there’s relatively less charge attraction from within

Question 48

The refractory period of a voltage gated ion channel occurs:

through rapid, automatic closing after opening
because the voltage gradient is gone

Answer 48

through rapid, automatic closing after opening

Question 49

Which corresponds to the voltage-gated ion channel conformation in response to depolarization?

closed
open
inactivated

Answer 49

open

Question 50

Which is responsible for the refractory period?

closed
open
inactivated

Answer 50

inactivated

Question 51

Channelrhodopsins can be engineered to respond to light by allowing movement of ions down their electrochemical gradients. A channelrhodopsin with a Cl- channel would cause:

deopolarization
opposition to any depolarizing stimuli

Answer 51

opposition to any depolarizing stimuli

Question 52

Channelrhodopsins can be engineered to respond to light by allowing movement of ions down their electrochemical gradients. A channelrhodopsin a Na+ channel would cause:

depolarization
polarization

Answer 52

depolarization

Question 53

This figure shows the open-times and current amplitudes from three separate channels (B) and also the aggregate current from all three channels (C). These data demonstrate that:

the amplitude of current from each individual channel is pretty much the same
the amplitude of current from each individual channel is random

Answer 53

the amplitude of current from each individual channel is pretty much the same

Question 54

This figure shows the open-times and current amplitudes from three separate channels (B) and also the aggregate current from all three channels (C). These data demonstrate that

the time each individual channel is open is the same
the time each individual channel is open is random

Answer 54

the time each individual channel is open is random

Question 55

This figure shows the open-times and current amplitudes from three separate channels (B) and also the aggregate current from all three channels (C). These data demonstrate that variability in aggregate current is mostly dependent on:

the time each individual channel is open
the current amplitude from each individual channel

Answer 55

the time each individual channel is open

Question 56

At the nerve terminal of the presynaptic neuron:

an action potential causes opening of voltage-gated Ca2+ channels, causing exocytosis of synaptic vesicles, releasing neurotransmitters into the synaptic cleft

binding of neurotransmitters opens ion channels on the postsynaptic target cell

Answer 56

an action potential causes opening of voltage-gated Ca2+ channels, causing exocytosis of synaptic vesicles, releasing neurotransmitters into the synaptic cleft

Question 57

At the plasma membrane of the postsynaptic target cell:

an action potential causes opening of voltage-gated Ca2+ channels, causing exocytosis of synaptic vesicles, releasing neurotransmitters into the synaptic cleft

binding of neurotransmitters opens ion channels on the postsynaptic target cell

Answer 57

binding of neurotransmitters opens ion channels on the postsynaptic target cell

Question 58

Transmitter-gated ion channels, also called ionotropic receptors, convert:

chemical signals from one cell into electrical signals in the target cell
electrical signals from one cell into chemical signals in the target cell

Answer 58

chemical signals from one cell into electrical signals in the target cell

Question 59

Common targets of excitatory neurotransmitters (which cause depolarization of target cells) are:

Na+ or Ca2+ channels
Cl- or K+ channels

Answer 59

Na+ or Ca2+ channels

Question 60

Common targets of inhibitory neurotransmitters (which cause polarization or oppose depolarization of target cells) are:

Na+ or Ca2+ channels
Cl- or K+ channels

Answer 60

Cl- or K+ channels

Question 61

Whether a given neurotransmitter is excitatory or inhibitory depends on the receptor it binds to. In some cells, acetylcholine binds a ligand-gated Na+ channel, causing it to open. This is:

excitatory
inhibitory

Answer 61

excitatory

Question 62

Whether a given neurotransmitter is excitatory or inhibitory depends on the receptor it binds to. In some cells, acetylcholine initiates metabotropic signaling leading to opening of plasma membrane K+ channels. This is:

excitatory
inhibitory

Answer 62

inhibitory

Question 63

The nicotinic acetylcholine receptors on the plasma membrane of skeletal muscle cells are non-selective and have the capacity to allow movement of Na+, Ca2+, or K+. In actuality, these channels predominantly allow movement of Na+ into the cells, because:

the tendency is for K+ to move out

the concentration of Na+ in the extracellular space is about 100 times greater than the concentration of Ca2+, so Na+ outcompetes Ca2+ for movement through the channel

Both of the above!

Answer 63

Both of the above!