chapter two, 17
pump that pumps heavy metals into vacuole for sake of cell. u make fake vesicle include the pump, put Zn2+ and ATP around it, K+ into in, and then you find Zn 2+ gets pumped into the vesicle.
then you vary the contents of the insides and outsides.
then you break the vesicles down, to find out the presence of turned on (phosphorylated) pumps
u take ones that are phosphorylated but don't have Zn outside, wash it out clean of ATP and then add Zn 2+
what do you think happens?
Small amount of Zn 2+ will move into the vesicle, no K+ will come out, protein pump becomes unphophorylated. pumps were activated previously w presence of Zn 2+ so Zn2+ gets stuck in, dephosphorylates the protein and gets spat out the other side, but absence of ATP means that the pump can't make the conformational change to take on the K+ and haul it out (assuming this works like Na+ K+ pump)
Antibodies that recognize the extracellular domain of Ca 2+ pump in animals blocks active transport of Ca2+ out of the cell. As a result, the intracellular contents of Ca 2+??Ca 2+ pumps in the ER membrane
keeps cytosolic Ca2+ conc. low.
is used to maintain pH in ANIMAL cells
20Na+ K+ transporter keeps both Na+ and Cl- out of the cell
by actively pumping out Na+ and keeping the outside so electropositive Cl- does not bother to enter.
21Ca 2+ pumps
in plasma membrane and ER are important
because they prevent Ca 2+ from altering activity of molecules in the cytosol.
(Ca 2+ is a very powerful signal molecule.
For uncharged molecule
, direction of diffusion decided solely by concentration gradient
For charged molecule
, it's conc. plus look at the membrane potential
Net driving force has 2 components
for charged molecule, it's called the electrochemical gradientCoupled transporters
use movement of a molecule flowing down
its gradient to power another going against
when transporter moves both ions in one direction
it's called a symport
if it moves one in, one out,
it's called a antiport
Movement of glucose into cell against conc. gradient can be powered w co-transport of Na+ into the cell.
movement of of Na+ ions from area o high concentration of low concentration is energetically FAVOURABLE, and increases entropy. As long as conc. in and out of the cell is significant, net entropy increase w d movement even though glucose going into area of higher glucose concentration results in loss of entropy
Testing rate of glucose transport into cell via Na+ glucose transporter.
In a vesicle, you have the pump put in right (glucose in, Na+ in) w glucose in vesicle and Na+ in the solution around it. You change conc. of the Na+ ions in the solution, and the rate of transport increases and then plateaus because the transporters reach a maximum capacity (become saturated) at which point maximum rate of transfer occurs, and rate will not increase regardless of addition of more Na+ ions outside.
If you also add leaky Na+ channels, the channels allow rapid equilibration of Na+ conc. in and out of the vesicle, destroying the gradient required for glucose transport, and so there will be no net movement of glucose regardless of how high the conc. of Na+solution.
open more frequently
in response to a given stimulus
Patch-clamp recording sons.
How do you set it up, and what does the 'clamp' refer to?
Requires removal of portion of cell membrane by sealing microelectrode to the cell membrane
. Pull the sealed portion away, place in solution of controlled medium. Voltage applied to patch o membrane can be fixed ('clamped') while varying other parameters for study.
Spikes in readings can be go either way
depending on the direction of flow of current
or manipulating the ion concentrations
on either side, which can result in negative readings for current when channels open.
- Gap Junctions ARE NOT large pores that connect cytosol to the outside. They connect the cytosols of adjacent cells. They are v large, and if they open straight up to extracellular space the permeability of cell membrane will be too high, affecting its effectiveness and selectivity
- Charged molecules / Ions CANNOT pass through aquaporins
- Selectivity of channel
depends on THREE (NOT ONE) parameters. Diameter
- Most ion channels ARE gated, depend on presence of stimulus to open or close and aren't jammed open allowing unregulated flow of ions.
Gating mechanism of auditory
hair cells is STRESS GATED
in skeletal cells is ligand-gated
ion channelStress-gated channels i
n hair cells of mammalian cochlea
responds to changes in membrane potential
Receptors for neurotransmitters
are mostly ligand
-gated channels are either completely open or completely closed.
In a resting cell, K+ leak channels
keep the electrochemical gradient of K+ at zero
32Nernst equation pls remember V = 62 × log(Co/Ci)
when co is 16 n ci is 106
V = 62 × log(15/106)
V = 62 × –0.849
V = –52.7
a BAD assumption when using Nernst equation is that the plasma membrane is primarily permeable to Na+. Buddy's got K+ leak channels, so it would be way more permeable to K+!!!!
If Na+ channels open in a previously at rest cell, membrane potential will become more POSITIVE.
Dendrites come out of the cell body of nerve cells, nerve terminals are the ends on the other side of axon, the long liney bit
Neurotransmitters ARE small molecules released into the synaptic cleft after fusion of synaptic vesicles w presynaptic membrane (the neuron sending the message)
Action potentials ARE NOT mediated by Ca 2+ channels, usually mediated by voltage-gated Na+
Voltage-gated Na+ channels ARE inactivated automatically shortly after activation so that action potential can't move backwards.
Voltage-gated K+ channels ARE NOT immediately opened in response to local depolarisation, they open when the action potential is at its peak so they can't weaken it, and instead help restore membrane potential while Ca 2+ channels are inactivated.
Voltage-gated Ca 2+ channels that respond to action potential are required for secretion of neurotransmitters. Depolarisation of nerve terminal causes Ca 2+ channels to open, Ca 2\; floods in, causes synaptic vesicles to fuse to plasma membrane and secrete lotsa neurotransmitters into the synaptic cleft
Threshold potential (-40mV) anything above me generates action potential
-60mV is resting membrane potential
spike of -40mv to 40mv is the action potential
between -60 to -40, the change from resting to threshold is the effect of the depolarising stimulus.
Action potential is wave of DEPOLARISATION.
Triggered when the membrane potential becomes LESS negative than resting membrane potential.
Propagated by the opening of VOLTAGE-GATED CHANNELS.
During action potential, membrane potential changes from NEGATIVE to POSITIVE.
Travels along the AXON to nerve terminals.
Signals received at DENDRITES what are on the nerve bodies.
the ACETYLCHOLINE neurotransmitter is the one released in the synaptic junctions between neurons and skeletal muscles.
neurotransmitters (like glycine n gaba) work by acting as ligands to open the gate for Cl-
so they rush in and neutralise the positive charge caused by influx of Na+ and kills the action potential in its tracks
Neurons communicate with each other through specialised sites called SYNAPSES.
Neurotransmitter receptors are ligand-gated ion channels that open transiently in POSTSYNAPTIC cell membrane in response to neurotransmitters released by PRESYNAPTIC cell. Ligand-gated ion channels convert CHEMICAL signals into ELECTRICAL signals. Neurotransmitter release stimulated by voltage-gated Ca 2+ channels in nerve terminal membrane.
Experiments on Squid Giant Axon
* In the cell you double the concentration of K+, plus Oac- that cannot go out that maintains the relative electrical balance within the cell. Does this make the membrane resting potential more negative or less?
MORE NEGATIVE. Increasing conc. of K+ in cell creates driving force for K+ to leave the cell, and the cell becomes more negative and the membrane potential becomes more negative.
* u double the amount of Na + outside another cell. How does this affect the action potential?
INCREASE HEIGHT of PEAK of action potential. Driving force to enter Na+ is higher than in usual circumstances, and when the Na+ channels open flux (rate) of Na+ ions moving into cells goes up.
* for yet another cell, u remove half of the Na+ natch present in that situation, and u add choline (v big cation that doesn't bother Na+ )
ACTION POTENTIAL HEIGHT will be LOWER than usual because halving the Na+ conc. reduces the driving force that pushes Na+ into the cell through the channels