chap12
No description yet. This curated deck is ready for daily study.
Card preview (24)
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 _.
small nonpolar oxygen carbon dioxide very small polar water large water-soluble ions
Transfer of nutrients, metabolites, and inorganic ions across cell membranes depends on _.
membrane transport proteins
Cell membranes contain a variety of transport proteins that function either as _ or _, each responsible for the transfer of a _ of solute.
transporters channels particular type
Channel proteins form _ across the lipid bilayer through which solutes can _.
pores passively diffuse
Both transporters and channels can mediate passive transport, in which an _ solute moves _
uncharged spontaneously down its concentration gradient.
For the passive transport of a charged solute, its _ determines its direction of movement, rather than its _ alone.
electrochemical gradient concentration gradient
An electrochemical gradient is the combined effect of two forces across a membrane: _ _
Concentration Gradient Electrical Gradient
Electrical Gradient:
Difference in charge across the membrane.
Concentration Gradient:
Difference in the amount of ions on each side.
Transporters can act as _ to mediate _ transport, in which solutes are moved _; this process requires _ that is provided by _ hydrolysis, a _, or _.
pumps _ active _ uphill against their concentration or electrochemical gradients _ energy _ ATP _ downhill flow of Na+ or H+ ions _ sunlight
Transporters transfer _ solutes across a membrane by _ that _ the solute-_ first on one side of the membrane and then _
specific undergoing conformational changes expose binding site on the other.
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 _.
out in steep drive other active transport processes electrical signals
Ion channels allow _ of _ size and charge to cross the membrane. Most are _ and open _ in response to a _.
inorganic ions appropriate gated transiently specific stimulus
Even when activated by a specific stimulus, ion channels _: they _ . An activating stimulus increases the _.
do not remain continuously open _ flicker randomly between open and closed conformations _ proportion of time that the channel spends in the open state _
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.
unequal charged ions flow through open ion channels
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 _.
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)
Higher Concentration Outside the Cell: _ _ _ Higher Concentration Inside the Cell: _ _
Na⁺ (Sodium) _ Ca²⁺ (Calcium) _ Cl⁻ (Chloride) _ K⁺ (Potassium) _ Various organic ions and proteins (contributing to a negative charge)
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.
voltage-gated Na+ and K+ channels sequentially depolarization
_ 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.
Voltage-gated Ca2+ channels Transmitter-gated ion channels
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.
transmitter-gated cation channels influx of Na+ depolarizes transmitter-gated Cl– channels depolarize
_ in the human brain exploit all of the above mechanisms to make human behaviors possible.
Complex sets of nerve cells
The rate at which a solute crosses a protein-free, artificial lipid bilayer by simple diffusion depends on its _ and _.
size solubility
which molecules pass the most without membrane proteins? and then? and then? and then?
SMALL, NONPOLAR MOLECULES (02, Co2) _ SMALL, UNCHARGED POLAR MOLECULES (H2O) _ LARGER UNCHARGED POLAR MOLECULES (glucose) _ IONS
Ion channels can exist in _
either an open or a closed conformation