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9/24/14 | Keller | Membrane Transport
Terms in this set (52)
The ionic composition of blood is very similar to the composition of ... .
The ionic difference separated by the membrane results in a ... ... .
Difference in the distribution of electrical charges between two points. Am I really making a flash card of this
Unit for potential
The net movement of positive charges per unit time (Amperes)
Unit for current
In a cell, an outward current implies...
A flow of positive charges from inside to outside (or a flow of negative charges from outside to inside... that's weird)
The difficulty of charges to move in a given medium
Unit for resistance
True or False: All living cells have a membrane potential (Vm)
The inside of cells is more ... than the outside of cells. (Referring to charge)
Embedded membrane proteins can either ... or ... move ions across the membrane.
Actively or passively
Three factors that determine membrane potential in cells
1. Concentration of ions on inside and outside
2. Passive permeability of ions through membrane through specific ion channels and transporters
3. Active transport of ions by electrogenic pumps (i.e. NA+/K+ ATPase, CA2+ transport pumps) that maintain the ion concentrations across the membrane by expending energy.
Three mechanisms allow ions and other lipid-insoluble molecules to cross the cell membrane
1. Channel-mediated passive xport
2. Carrier-mediated passive xport
3. Carrier-mediated active xport
Passive transport relies on ... .
Ion channels can be viewed as ... that allow charged molecules to move across the cell membrane
Pores. Srsly why am I making flashcards for this
The nature of the protein ... components provides a means to distinguish channel subtypes
The Nicotinic Cholinergic Ion channel is a ...-... ion channel
(It relies on the binding of acetylcholine on the outside for its open/shut shenanigans)
A typical voltage-gated ion channel is constructed from ... different subunits
True or False: Most ion channels are selective to the ion(s) they permit to pass through them
The selectivity exhibited by ion channels is derived from 2 factors
1. Size of the pore (ions may be selected by virtue of their overall size)
2. Amino acid composition in the pore walls (residues may form weak bonds with specific ions, limiting passage to only those who are bound)
Although Na+ is actually smaller than K+, the ... ... is larger than that of K+, preventing passage through a K+ channel.
What characteristics of ions are involved in its binding affinity with ion channels?
Charge, structure, hydrogen bonding
The gate of an ion channel provides access to the ... and determines ... ions can flow through the pore
True or False: Most ion channels are not gated.
False. They totally mostly are.
(Fun fact: Gates can be closed, open, or inactive)
Opening and closing of ion channels usually involve ... changes in the gate
Three mechanisms by which channels are gated.
Example of non-gated channel
K+ channels in glial cells that remove excess K+ from extracellular space
Example of an extracellular ligand-gated ion channel
Neurotransmitter receptor (involves antiport of Na+ to inside, K+ to outside after glutamate binds)
Two examples of intracellular ligand-gated ion channels
1.Ca2+-activated K+ Channel (Ca2+ binds, K+ goes bye bye)
2. Cyclic nucleotide gated channel (cAMP binds, Na+ / K+ antiport madness)
Where is the Nicotinic Cholinergic Ion Channel important?
At the neuromuscular junction
(Signal for muscular contraction)
Is the Nicotinic Cholinergic Ion Channel specific for a certain molecule?
Primarily Na+ but some K+ also
(ACh binds, opens channels, Na+ flows in and depolarizes cell of post-synaptic cell)
What allows exocytosis to occur from the pre-synaptic vesicle?
Ligand-gated calcium channel
Four molecules discussed that have associated voltage-gated channels
What occurs to allow a voltage-gated channel to open?
Change in potential across a membrane
Example of mechanically-gated ion channel
Auditory hair cells (stereocilia)
How do auditory hair cells work?
Tipping of a hair cell due to sound can open a channel and change membrane potential
How do swelling-activated channels work?
Cell swelling leads to opening of stretch-activated channels. Ions flow out, water follows, cell shrinks
... are necessary for a membrane potential
(Need some current to flow to create a potential difference. Semipermeable membrane able to accomplish this)
In a real cell, what ion is "leakiest" (and thus helps create the current to flow to create a potential difference?)
In regard to membrane potential in a cell, describe the + effect and - effect in respect to K+
+ Effect = K+ is driven out of the cell by the concentration gradient
- Effect = K+ is attracted by the negative charges within the cell and repelled by the positive charges outside
What is patch clamp recording?
Records current from single ion channels. They are distinctly open or closed (binary).
True or False: There are several ligand-gated Na+ channels as well as voltage-gated Na+ channels
Two examples of voltage-gated Na+ channel blocker
1. Local anesthetics (lidocaine)
2. Tetrodotoxin (irreversible! unlike #1)
Facilitated transport utilizes 3 different types of ion transporters (carriers)
(last two are termed coupled xport)
True or False: Sodium running down its gradient carries glucose against its gradient.
Name one similarity, one difference between carriers and channels
Carry specific ions or molecules
Can be inhibited by specific inhibitors
Carriers exhibit saturation, whereas in channels, an increase in concentration results in a simple increase in diffusion rate
Amount of Na+ / K+ per ATP in ATPase?
3Na+ out / 2K+ in
True or False: The Na+/K+ ATPase contributes significantly to the Vm.
(Although it is electrogenic (i.e., generates flow of current through the membrane -brings 3 "+" charges in for every 2 it moves out), its participation in Vm is negligible.)
Ion channels and ion transporters can be thought of as ... ... - because the transported ion (such as Na+) flowing down it's concentration gradient must eventually be re-established by an active system (such as the Na + /K + pump).
In addition to Na+/K+ ATPase, what are other examples of active transport?
Ca2+-ATPases (present on cell membrane and ER! U know dis! Reduce cytosolic Ca2+ levels.)
H+-ATPases (used in maintaining cytosolic pH. Usually done in exchange for K+)
True or False: Can't have a huge change in the sodium concentration in a cell (i.e. sodium channel open very long) because it takes a long time for ATP-powered pumps to reestablish equilibrium
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