Ch 12 Molec Cell Smartwork Questions (Exam 2)

What forms tiny hydrophilic pores in the membrane through which solutes can pass by diffusion?

channels

Solutes that are small enough to pass through the channel will

diffuse through

• those that are too large will not

Lipid bilayers are highly impermeable to what molecules?

Na+ and Cl-

What inhibits inorganic molecules, such as Na+ and Cl-, from passing through a lipid bilayer?

the hydrophobic interior of the lipid bilayer

Small, nonpolar molecules, such as O2 and CO2 diffuse

rapidly across lipid bilayers

Sodium ions, O2, and glucose pass directly through lipid bilayers at different rates. What order do they go in, from fastest to slowest?

oxygen, glucose, sodium ions

Na+ is the

most plentiful positively charged ion outside the cell

K+ is the

most plentiful positively charged ion inside the cell

What is the voltage difference across a membrane of a cell called?

membrane potential

Each type of cell membrane has its own characteristic set of

transport proteins which determine which solutes can pass into and out of that cell or organelle

How do channels select which solute they help move across the membrane?

channels discriminate between solutes mainly on the basis of size and electric charge

How do transporters select which solute they help move across the membrane?

transporters bind their solutes with great specificity in the same way an enzyme binds its substrate

The movement of an ion down its concentration gradient is called what?

passive transport

The movement of an ion against its concentration gradient is called what?

active transport

What requires an input of energy to occur?

the movement of a solute from a region of lower concentration on one side of a membrane to a region of higer concentration on the other side

All other factors (conc., solute size, etc.) being unequal, which type of solute does a cell tend to pull inside?

positively charged solutes

In passive transport, the net movement of a charged solute across the membrane is determined by what?

its electrochemical gradient

The net force driving a charged solute across a cell membrane includes

its concentration gradient and membrane potential

• together determined the electrochemical gradient

Osmosis is the

movement of H2O from an area of low solute concentration to an area of high solute concentration

Na+ and ATP are

inside the liposome

K+ is

outside the liposome

GTP and Cl- are

unneeded in the liposome

Small, nonpolar molecules include

O2, CO2, N2, and steroid hormones

Small, uncharged polar molecules include

H2O, ethanol, and glycerol

Larger uncharged polar molecules include

glucose, nucleosides, and some amino acids

Ions include

H+, Na+, K+, Cl-, etc

The Na+ pu,p in the plasma membrane of animal cells uses energy from ATP hydrolysis to pump sodium and potassium ions against their electrochemical gradients. In which direction are the ions pumped across the membrane?

Na+ out and K+ in

Na+ is at a

higher concentration outside the cell

K+ is at a

higher concentration inside the cell

ATP is hydrolyzed in

the cytosol and K+ is pumped into the cell during the pump cycle

In most animal cells, which ion can move through “leak” channels?

K+

Auditory hair cells in the ear depend on what type of ion channel to detect sound vibrations?

mechanically-gated

For voltage-gated channels, a change in the membrane potential alters the

probability that the channel will be found in its open conformation

To pass through the pore of an ion channel, what must be true of an ion?

it must interact with polar groups in the narrowest part of the channel

During an action potential, what action does NOT help return the membrane to its resting potential?

the opening of voltage-gated NA+ channels

The opening of voltage-gated Na+ channels promotes

depolarization, not repolarization

What activities help restore the ion gradients across the plasma membrane of an axon after an action potential has occured?

the action of Na+ pumps

Following an action potential, a nerve cells goes through a brief refractory period during which it cannot be stimulated. What is true during this refractory period?

voltage-gated Na+ channels in the nerve cell membrane are inactivated

What is a difference between transporters and channels?

transporters can facilitate both active or passive transport of solutes; channels facilitate only passive transport

Cells, compared with the extracellular fluid are

slightly negatively charged

An extracellular molecule binds to a channel and triggers it to move more often to the conformation than the closed conformation, this is referred to as a

ligand-gated channel

Which organelle is important for controlling the concentration of calcium ions in the cytosol?

endoplasmic reticulum

The glucose-Na+ symporter in epithelial cells uses the electrochemical gradient of Na+ to draw glucose into the cell. True or false?

true

When the glucose-Na+ symport protein is in its outward-open state, what is likely to occur?

Na+ binds to its binding site

Because Na+ concentrations are high outside the cell,

Na+ readily binds to the transporter in its outward-open state

Inhibitory neurotransmitters such as glycine and GABA make a postsynaptic cell harder to depolarize by allowing what?

an influx of Cl-

Transmitter-gated ion channels are insensitive to membrane potential; in the absence of neurotransmitters, they cannot generate an action potential. True or false?

true