chap12

Question 1

The lipid bilayer of cell membranes is highly permeable to _, _ molecules such as _ and _ and, to a lesser
extent, to _, _ molecules such as _. It is highly impermeable to most _, _ molecules and to all _.

Answer 1

small
nonpolar
oxygen
carbon dioxide
very small
polar
water
large
water-soluble
ions

Question 2

Transfer of nutrients, metabolites, and inorganic ions across cell membranes depends on _.

Answer 2

membrane transport proteins

Question 3

Cell membranes contain a variety of transport proteins that function either as _ or _, each responsible for the transfer of a _ of solute.

Answer 3

transporters
channels
particular type

Question 4

Channel proteins form _ across the lipid bilayer through which solutes can _.

Answer 4

pores
passively diffuse

Question 5

Both transporters and channels can mediate passive transport, in which an _ solute moves _

Answer 5

uncharged
spontaneously down its concentration gradient.

Question 6

For the passive transport of a charged solute, its _ determines its direction of movement, rather than its _ alone.

Answer 6

electrochemical gradient
concentration gradient

Question 7

An electrochemical gradient is the combined effect of two forces across a membrane:

_
_

Answer 7

Concentration Gradient
Electrical Gradient

Question 8

Electrical Gradient:

Answer 8

Difference in charge across the membrane.

Question 9

Concentration Gradient:

Answer 9

Difference in the amount of ions on each side.

Question 10

Transporters can act as _ to mediate _ transport, in which solutes are moved _; this process requires _ that is provided by _ hydrolysis, a _, or _.

Answer 10

pumps
_
active
_
uphill against their concentration or electrochemical gradients
_
energy
_
ATP
_
downhill flow of Na+ or H+ ions
_
sunlight

Question 11

Transporters transfer _ solutes across a membrane by _ that _ the solute-_ first on one side of the membrane and then _

Answer 11

specific
undergoing conformational changes
expose
binding site
on the other.

Question 12

The Na+ pump in the plasma membrane of animal cells is an ATPase; it actively transports Na+ _ of the cell and K+ _, maintaining a _ Na+ gradient across the plasma membrane that is used to _ and to convey _.

Answer 12

out
in
steep
drive other active transport processes
electrical signals

Question 13

Ion channels allow _ of _ size and charge to cross the membrane. Most are _ and open _ in response to a _.

Answer 13

inorganic ions
appropriate
gated
transiently
specific stimulus

Question 14

Even when activated by a specific stimulus, ion channels _: they _ . An activating stimulus increases the _.

Answer 14

do not remain continuously open
_
flicker randomly between open and closed conformations
_
proportion of time that the channel spends in the open state
_

Question 15

The membrane potential is determined by the _ distribution of _ on the two sides of a cell membrane; it is altered when these ions _ in the membrane.

Answer 15

unequal
charged ions
flow through open ion channels

Question 16

In most animal cells, the _ value of the resting membrane potential across the plasma membrane depends mainly on the _ and the operation of _; at this resting potential, the driving force for the movement of K+ across the membrane is _.

Answer 16

negative
K+ gradient
K+-selective leak channels
almost zero (the concentration gradient pushing K+ out and the electrical gradient pulling K+ back in= balanced forces)

Question 17

Higher Concentration Outside the Cell:
_
_
_
Higher Concentration Inside the Cell:
_
_

Answer 17

Na⁺ (Sodium)
_
Ca²⁺ (Calcium)
_
Cl⁻ (Chloride)
_
K⁺ (Potassium)
_
Various organic ions and proteins (contributing to a negative charge)

Question 18

Neurons produce electrical impulses in the form of action potentials, which can travel long distances along an axon without weakening. Action potentials are propagated by _ that open _ in response to _ of the plasma membrane.

Answer 18

voltage-gated Na+ and K+ channels
sequentially
depolarization

Question 19

_ in a nerve terminal couple the arrival of an action potential to neurotransmitter release at a synapse. _ convert this chemical signal back into an electrical one in the postsynaptic target cell.

Answer 19

Voltage-gated Ca2+ channels
Transmitter-gated ion channels

Question 20

Excitatory neurotransmitters open _ that allow the _, which _ the postsynaptic cell’s plasma membrane and encourages the cell to fire an action potential. Inhibitory neurotransmitters open _ in the postsynaptic cell’s plasma membrane, making it harder for the membrane to _ and fire an action potential.

Answer 20

transmitter-gated cation channels
influx of Na+
depolarizes
transmitter-gated Cl– channels
depolarize

Question 21

_ in the human brain exploit all of the above mechanisms to make human behaviors possible.

Answer 21

Complex sets of nerve cells

Question 22

The rate at which a solute
crosses a protein-free, artificial lipid
bilayer by simple diffusion depends on
its _ and _.

Answer 22

size
solubility

Question 23

which molecules pass the most without membrane proteins?
and then?
and then?
and then?

Answer 23

SMALL, NONPOLAR MOLECULES (02, Co2)
_
SMALL, UNCHARGED POLAR MOLECULES (H2O)
_
LARGER UNCHARGED POLAR MOLECULES (glucose)
_
IONS

Question 24

Ion channels can exist in _

Answer 24

either an open or a closed conformation

Question 25

Solutes cross cell membranes by either _ or _ transport.

Answer 25

passive
active

Question 26

Some small, nonpolar molecules such as CO2 (see Figure 12–2) can move passively down their concentration gradient across the lipid bilayer by _, without the help of a membrane transport protein.

Answer 26

simple diffusion

Question 27

Most solutes, however, require
_

Answer 27

the assistance of a channel or transporter.

Question 28

Passive transport, which allows solutes to move down their concentration gradients, occurs _; active transport against a concentration gradient requires an _

Answer 28

spontaneously
input of energy.

Question 29

_ can carry out active transport, and the _ that perform this function are called _.

Answer 29

Only transporters
transporters
pumps

Question 30

Pumps carry out active transport in three main ways:

Answer 30

gradient-driven pump (secondary active transport)
_
ATP-driven pump (primary active transport)
_
LIGHT-driven pump

Question 31

The Na pump uses the
energy of _ to pump Na+
_ of animal cells and K+ _.

Answer 31

ATP hydrolysis
out
in

Question 32

When a muscle
cell is stimulated, _ floods into the cytosol from the sarcoplasmic reticulum—a specialized form of endoplasmic reticulum.

Answer 32

Ca2+

Question 33

The influx of Ca2+ stimulates the muscle cell to contract; to recover from the contraction, Ca2+ must be pumped back into the sarcoplasmic reticulum by _.

Answer 33

this Ca2+ pump

Question 34

The Ca2+ pump uses _ to phosphorylate _, inducing a _; when the pump is open to the lumen of the sarcoplasmic reticulum, the Ca2+-binding sites are eliminated, _

Answer 34

ATP
_
itself
_
series of conformational changes
_
ejecting the two Ca2+ ions into the organelle (out of the cell).

Question 35

Two types of glucose transporters enable gut epithelial cells to transfer glucose across the epithelial lining of the gut: (fig 12.17)

Answer 35

GLUCOSE IS ACTIVELY TAKEN UP FROM GUT
_
GLUCOSE IS PASSIVELY RELEASED FOR USE BY OTHER TISSUES

Question 36

Na+ that enters the cell via the Na+-driven glucose _ is subsequently pumped out by _ in the _ plasma membranes (fig 12.17)

Answer 36

symport
Na+ pumps
basal and lateral

Question 37

The _ and _ play major parts in generating the resting membrane potential across the plasma membrane in animal cells.

Answer 37

K+ concentration gradient
K+ leak channels

Question 38

gradient and K+ leak channels play major parts in generating the _ in animal cells.

Answer 38

resting membrane potential across the plasma membrane

Question 39

What happens when K+ channels are closed in a cell membrane?

Answer 39

No movement of K+ occurs across the membrane, so the membrane potential is zero, with balanced charges on both sides.

Question 40

What happens when K+ leak channels open?

Answer 40

A: K+ ions move out of the cell due to the concentration gradient, making the inside of the cell more negative

Question 41

What is the resting membrane potential?
_

Answer 41

A: It’s the stable membrane potential where the electrical gradient (pulling K+ in) and concentration gradient (pushing K+ out) are balanced, with no net movement of K+.

Question 42

_ change their conformation during an action potential.

Answer 42

Voltage-gated Na+ channels

Question 43

Note that an action potential can only travel forward; that is, away from the site of depolarization. This is because _ prevents the advancing front of depolarization from spreading backward

Answer 43

Na+ channel inactivation in the aftermath of an action potential