Williamson - Membranes Flashcards
what is a membrane raft, which phospholipids
thicker more rigid patch of membrane, contains more sphingolipids and cholesterol
what proteins associate with membrane rafts
those with long TM helices
GPI anchors
palmitoyl anchors
NOT prenylated anchors
how can you find membrane rafts
AFM (atomic force microscopy)
what can a membrane raft do
organise proteins
signal
trafficking - endocytosis
how does endocytosis occur
protein dimerises and brings lipid rafts together
caveolin proteins bind to one side (inner) causing a curve
more proteins recruited into coat
pinched at the top
what does patch clamping measure
the current across a membrane
what does inside out patch clamping geometry measure
current across the patch of inner leaflet membrane
what does outside out measure
current across outer leaflet membranes - useful for ligand gated channels - can put ligands in the solution
what does whole cell geometry patch clamping measure
current across the whole cell
what is the concentration of sodium inside and outside the cell
inside: 12mM
outside: 150 mM
what is the concentration of potassium inside and outside the cell
inside: 140 mM
outside 4 mM
when is the peak of action potential
when sodium channels close and potassium channels open
how does the Na+/K+ pump maintain the resting potential
it pumps 3 sodium out for every 2 potassium in maintaining ratio of sodium to potassium which is much lower that outside the the cell (against their concentration gradients)
inside: 150mM:4mM
outside: 12mM:140mM
what causes a cell to be hyperpolarised
a rush of K+ out of the cell
how would you characterise a voltage-gated channel
using whole cell patch clamping
vary voltage applied
and measure the currents
how would you characterise a ligand gated channel
using outside-out patch clamping
different ligands (and different concs) in the buffer solution
measure current
What K+ and Na+ channels/pumps are present in nerve cells
Na/K pump 3 Na+ for 2 K+
voltage gated Na+ channel –> action potential
voltage gated K+ channel –> repolarisation
K+ resting channel
what is the refractory period
a temporary period after an action potential when the membrane is unresponsive and unable to generate another action potential. This allows the cell to recover and ensures action potentials propagate in one direction.
Due to plug in sodium channel
4ms
what is hyperpolarisation
membrane potential is very negative (-70mV) making the cell less likely to generate an action potential
caused by resting K+ channel
what is repolarisation
when sodium channels are closed but potassium channels are open
membrane potential decreases from the peak (action potential)
what is depolarisation
change in cell membrane potential, making it more likely to generate an action potential
when the threshold (-55mV) is met and Na+ channels rapidly open - action potential (+30mV)
where does the energy come from to maintain the action potential along an axon
ATP powering the Na+/K+ pump
what are the structure features behind a voltage-gated channel
voltage sensing domains: eg. charged AAs, undergo structural changes to open or close the channel pore
selectivity filter for their ion
why is the potassium leak channel important
to maintain the resting potential
negative inside the cell
K+ can leave, leaving behind a negative charge
