What is the approximate concentrations of Na+ and K+ inside and outside the cell? -
answer✔inside cell:
140 mM K+
4 mM Na+
outside cell:
140 mM Na+
4 mM K+
What is the freeze fracture procedure? - answer✔a sharp knife is used to break apart frozen
tissue along the membrane, separating the bilayer at some parts. The tail surface of the inner
leaflet is known as the P face, and the tail surface of the outer layer in the E face. Some integral
proteins will remain embedded in these faces, while other will have been pulled off leaving
indents in the surface. This exposes the inside of the leaflets for examination
What part of the membrane is glycosylated? - answer✔only lipids and proteins on the
extracellular side are glycosylated. About 2-10% of membrane by weight.
what is the lipid bilayer mainly composed of? - answer✔phospholipids, cholesterol and
glycolipids
what happens when a lipid bilayer is torn? - answer✔it spontaneously reseals
What effect do kinks in the phospholipids of the lipid bilayer have on the rate of lateral
diffusion? - answer✔it promotes lateral diffusion, since the kinks reduce interactions between
phospholipids, and thus make it more difficult to pack them tightly together
Is cholesterol found in bacteria cell membranes? - answer✔No, only of eukaryotes
at the same time, it separates phsopholipids from eachother preventing them from interacting too
closely, thus it adds to the fluidity of the membrane
What is the role of glycolipids in the lipid bilayer? - answer✔only in the outer portion of the
bilayer. plays a role in cell metabolism, formation of myelin sheaths and membrane turnover
what % of membrane mass is made up of by proteins? - answer✔usually about 50%,
for myelin, less (25%)
for inner mitochrondrial membrane more (75%)
What are the 2 major classes of membrane proteins and how are they removed? -
answer✔integral (in the membrane): harder to remove, need to disrupt the whole membrane via
detergent
peripheral (on outside of membrane: easy to remove, removed by high [salt] which breaks the
bond between the protein and the lipid
How do detergents remove integral proteins from the lipid bilayer? - answer✔detergent
molecules are similar to phospholipids, they replace them in the lipid bilayer at some places. If
they are next to a protein they can form a complex, then upon removal of the detergent they may
cause the protein to precipitate
How doe the mobility of membrane proteins compare to phsopholipids? - answer✔Similar,
they can rotate on their axis, they can diffuse laterally but not flip-flop
they diffuse much slower though, because they are much bigger (40x slower)
Their mobility is sometimes hindered if they are connected to actin
how can you measure the mobility of proteins in the lipid bilayer? - answer✔FRAP
fluorescently label the proteins, bleach an area with a stong light, then see how fluorescence
recovers
What is the role of carbohydrates in the lipid bilayer? - answer✔They act cell-cell interactions,
recognition etc.
small polar, uncharged molecules CAN SOMEWHAT (except H2O)
large polar, uncharged molecules CANNOT (glucose)
hydrophobic molecules CAN
What are the different ways in which a channel can be gated? - answer✔ligand, voltage or
mechanically (stretch or compression operated)
What are gap junctions? - answer✔hemichannels formed between 2 cells, made up of connexin
aggregates. Conducts current and small molecules
What are common surface proteins of a membrane, intrinsic proteins and cytoplasmic proteins? -
answer✔surface: fibronectin, N-CAM, proteoglycans
intrinsic: ion channels, receptors, transporters, enzymes, gap jxns
cytoplasmic: actin, ankyrin
What acts as a resistor and what acts as a capacitor in the cell model? - answer✔The channels
act as resistors, and the membrane acts as a capacitor
What is voltage (V)? - answer✔The electrical potential or driving force (V)
What is Ohm's law for voltage change across a resistor? - answer✔V=ir
What happens to voltage as it passes through a resistor? Use the analogy to the pipe -
answer✔Voltage drops as it passes through a resistor. It is similar to how lengths of pipe that
are more narrow than the rest, where the pressure drops
What is total resistance for resistors in series? In parallel? - answer✔In series: R(tot)=R1 +
R2...
in parallel: 1/R(tot)=1/R1 + 1/R2...
How does a capacitor store charge? - answer✔A current of negatively charged electrons is
repelled away from the negative end of a battery, and accumulate onto one side of a capacitor.
The electric field attracts positive charges to acumulate on the other side of the capacitor.
How can charge that a capacitor holds be increased? What's the max charge it can hold? -
answer✔by increasing the SA of the plates. Also by decreasing the thickness of the insulator so
that the plates are closer together.
What is capacitance (c)? - answer✔A measure of how much charge can be stored at a capacitor
for a given voltage applied.
c=q/V (c is measured in Farads (F))
don't mix (c=capacitance) with (C=coulombs)
What does an open ion channel act as in a membrane? A closed channel? An ion channel who's
conductance can be regulated by voltage or ligands? - answer✔open ion channel: a resistor
closed ion channel: an open circuit (open meaning incomplete) (b/c there's infinitely large
resistance)
ion channel whos conductance can be regulated by voltage or ligands: a variable resistor
What does r//c mean? - answer✔a resistor and capacitor in parallel
What does the electrical model of a piece of membrane with one or more conducting ion
channels look like? - answer✔extracellular fluid on one side and cytoplasm on the other, with a
resistor (channel) and capacitor (membrane) in parallel separating the two.
NOTE THAT THE MEMBRANE RESISTANCE IS EQUAL TO THE INPUT RESISTANCE.
ALSO NOTE THAT THIS IS WHEN THERE IS NEGLIGIBLE CYTOPLASMIC AND
EXTRACELLULAR RESISTANCES AND THERE ARE NO VOLTAGE DEPENDENT
CHANNELS
What is the typical value of resistance of an open channel in a membrane? What about
conductance? - answer✔2-500 GΩ
g=1/r so 500-2 pS
What is the specific capacitance of biological membranes? - answer✔about 1 uF/cm^2
How much charge can a typical membrane capacitance hold if the resting potential is -80mV?
What would this be in # of mols? What about # of ions? - answer✔c=q/V
q=c x V
q=1uF/cm^2 x 80mV
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