Chapter 12 Flashcards
Lipid bilayers are impermeable to
Solutes and ions
Membrane transport proteins fall into two classes:
transporters and channels
Solutes cross membrane by either
Passive or active transport
What concentrations are high outside the cell
Na, Cl, Mg, Ca
What concentration is high inside the cell
K
The rate at which a molecule crosses a lipid bilayer depends on its
Size and solubility
Membranes are permeable to
Small, hydrophobic and uncharged molecules
Membranes less permeable to
Large, polar molecules and ions
change shape to move solutes
Transporters
Can be passive or active
Transporters
Function as pores
Ion channel
Ion channels are always
Passive
What gradient drives transport
Electrochemical
Movement of charged molecules depends on
Both the concentration and electrical gradient
Transitions between conformations are
Random, reversible, and don’t depend on solute binding
move solutes across the membrane
along their electrochemical gradients (no ATP required)
Passive transporters
actively transport solutes against their
electrochemical gradients (requires an input of energy, like ATP)
Pumps
use a gradient of one solute across a
membrane to drive the active transport of a second molecule
Coupled pumps
Glucose transporter mediates
Passive transport
Because __ is uncharged, the electrical component of its electrochemical gradient is zero.
glucose
transport moves solutes against their electrochemical
gradients (e.g., moving Na + out of the cell)
Active
Animal cells use __ to pump Na + out and K+ in
ATP Hydrolysis
The __ is driven by a cycle of phosphorylation and dephosphorylation
Na+-K+ pump
helps maintain the osmotic balance of animal cells
Na+-K+ pump
Intracellular Ca2+ concentrations are kept
Low by Ca pumps (driven by atp hydrolysis)
The Glucose-Na+ symport is a
Coupled pump
uses energy from transporting Na+ along its electrochemical gradient to transport glucose against its gradient
Glucose Na symport
drive membrane transport in plants, fungi, and
bacteria
Proton (H+) pumps
Na K pump, pumps what in and out
3 Na out and 2 K ions against gradients
__ drives conformational changes
Phosphorylation
Ca2+ ATPase/pump reduces
cytosolic calcium
Ca2+ ATPase/pump located in the
ER membrane and membrane
Cytosolic levels must be kept
Low
Calcium concentration important for
Cell signaling
A gradient of any solute across a membrane can be used to drive the active transport of a second molecule
Coupled pumps
use ion gradients to drive the active transport
of two solutes in the same or opposite direction
Symport & antiport
passive transport of one solute
Uniport
Coupled transporters use __ to take up nutrients actively
ion gradients
Glucose-Na+
symport in apical
membrane
Active
Glucose uniport in
basal membrane
Passive
Na+-K+ pump
maintains ion
gradients by
hydrolyzing ATP
Active
What determines the direction of passive transport across
the membrane?
The electrochemical gradient of the solute
Pumps actively transport solutes __ their electrochemical gradients
against
couples the transport of one solute against
its electrochemical gradient with the transport of another solute along its electrochemical gradient
Gradient driven/coupled
Three types of active transport
Gradient driven, atp driven, or light driven
uses energy from ATP hydrolysis
ATP driven
2 types of gradient-driven pumps, based on the direction of coupled transport:
Symport and aniport
Glucose transporter is __ and an example of a __
Passive, uniport
Active transporters atp driven
Na/K, Ca ATPase and H pump
Ca2+ ATPase moves what
2 ions out of cell or into the ER
Active transporters gradient driven
Glucose Na symport
The movement of an ion down its electrochemical gradient is
a form of active transport.
T or F
False, passive
Coupled transporters use electrochemical gradients to drive active transport of other solutes.
T or F
True
The transport of glucose across the membrane can be active
or passive, depending on the nature of the transporter. T or F
True, active is glucose sodium symport and passive is glucose transporter
Ion channels are
selective and gated
Ion channels randomly…
snap between open and closed
VG ion channels respond to the
membrane potential
Small pores that filter ions by size and charged
ion channel
The frequency of opening and closing of an ion channel depends on the
presence of a specific stimulus
what channel responds to neurotransmitters binding
ligand gated
what channel responds to mechanical stimulus
mechanically or stress gated channel
What accounts for RMP
K leak channels
if a membrane is permeable to an ion, then the membrane
potential is
determined by the Nernst equation
The nerst equation is dependant on the
ratio of ion concentration outside vs. inside
In a resting cell, the Nernst equation is determined by
K
In the ear, sound vibrations on auditory hair cells opens what channel
stress gated ion channels, leading to AP
Tilting the stereocilia in the ear in response to sound vibrations has what effect
pulls on linking filament, opening ion channel
Action potentials are usually mediated by
voltage-gated Na+
channels
Voltage-gated Ca2+ channels convert
electrical signals into
chemical signals at nerve terminals
Ligand-gated channels in target cells convert
chemical signals back
into electrical signals
Neurons receive what kind of inputs
excitatory and inhibitory
major targets for psychoactive drugs
Ligand-gated ion channels (transmitter)
Action potentials are converted into __ signals
via the release of neurotransmitters at the nerve terminal
electrical converted into chemical
When a neuron is stimulated, the membrane potential of the plasma membrane shifts to a
less negative value
After opening, Na+ channels rapidly become
inactivated
The Na+ channels remain in the inactivated state until the
membrane potential
has returned to its resting, negative value
Action potential only moves in
1 direction
prevents the action potential from moving backwards
Na+ channel inactivation
channels at nerve terminals
of pre-synaptic cell
Voltage-gated Ca2+
Convert electrical signal (ions from the action potential) to a chemical signal
(neurotransmitter)
voltage gated calcium channels
The acetylcholine (Ach) receptor is a
transmitter-gated ion channel
After Ach binds to a channel what happens
influx of sodium, causing AP
Influx of __ tends to keep the membrane polarized, decreasing firing of an action potential
Cl, inhibitory synapse
Excitatory synapse has what ion
sodium
Acetylcholine and glutamate are __ neurotransmitters, bind __ channels
excitatory, ligand-gated
cation
GABA and glycine are __, bind __ channels
inhibitory, ligand-gated Cl-
