2.2: Membrane Proteins and Transport across Membranes Flashcards
what are the two classes of membrane transport proteins
channel proteins, transporters (uniporters, symporters and antiporters, atp driven pumps)
is the artificial bilayer impermeable or permeable to most water soluble molecules
impermeable
can water soluble molecules conduct simple diffusion across the bilayer quickly
no, it takes a long time which is too slow for most functions
what is the term of transport/regulation of membrane transport proteins transferring specific molecules
facilitated transport
what type of molecules are permeable across the lipid bilayer (simple diffusion)
small nonpolar molecules (hydrophobic – o2, co2, n2, steroid, hormones), small uncharged polar molecules (h2o, ethanol, glycerol)
are large uncharged polar molecules (aa, glucose, nucleosides) and ions permeable or impermeable across the lipid bilayer
impermeable
are transport proteins selective
yes
what determines the selectivity of the channels and transporters
channels: size and electric charge of solute
transporters: solute fits into the binding site
organize the following into passive or active transport and determine whether it follows concentration gradient:
simple diffusion
channel mediated
transporter mediated
simple channel and channel mediated can be passive
transporter can be active
passive follows gradient and active doesn’t
⭐️what composes the electrochemical gradient aka the voltage gradient
NET DRIVING FORCE
concentration gradient + membrane potential (electrical gradient)
side note: Eg glucose - uncharged molecules so it can also be determined by the concentration gradient
Molecules must have a charge in order to have an electrochemical gradient
describe the additive nature of the electrochemical gradient and what is the opposite
the additive nature is when there is strong net driving force bc the transported molecules are moving to the side complementary to their charge
the opposite is when they work against each other and they are trying to transport molecules to the side with the like charge
which side of the cell negatively and which is positively charged
inside is -, outside is +
channel proteins are a ____________ pore across the membrane (hydrophilic or hydrophobic)
hydrophilic
describe channel proteins in terms of selectivity, speed, and interactions with the channel
- they are selective, eg ion channels based on ion size and electric charge
- selectivity happens at the center, they have to fit (eg k ions have to shed h2o to fit)
- transient interactions with the channel wall
- faster transport through channels
what type of ion channel is k+ leak channels and its significance to membrane potential
non gated ion channels
[c] of k+ in cytosol is always relatively higher so it’s always leaking out = sets up membrane potential
describe non gated ion channels
- always open
- k+ leak channels: k+ moves out of cell, found in plasma membrane of animal cell,
what type of ion channels are the following:
mechanically gated
ligand gated (intracellular and extracellular)
voltage gated
gated ion channels
for voltage gated ion channels, can they flip back and forth
yes. can also randomly flip back and forth in the open or closed conformation so its really about what the steady state it’s in when there is or is not a signal
what is the signal for the following:
mechanically gated
ligand gated (intracellular and extracellular)
voltage gated
mechanically gated - mechanical stress (plasma membrane stretched to open channel)
ligand gated extracellular - ligand eg nt (outside is the gate)
ligand gated intracellular
ligand eg ions, nucleotide (inside is the gate)
voltage gated - change in voltage across the membrane (membrane depolarization)
describe the differences in rate of transported mediated diffusion and simple diffusion and channel mediated transport
simple diffusion and channel mediated transport is linear while transport mediated is similar to log as approaches max
associate the following examples to what form of membrane transport they are
- k+ leak channels
- glut uniporter
- Na+ glucose symporter
- Na+ H+ exchanger
- Na+ K+, H+ Pump
passive transport by channel proteins: k+ leak channels
passive transport by transporter proteins: glut uniporter
active transport by gradient driven pumps (transporter proteins): Na+ glucose symporter
active transport by gradient driven pumps (transporter proteins): Na+ H+ exchanger (antiport)
active transport by ATP driven pumps (transporter proteins) Na+ K+, H+ Pump
describe the uniport process of transport
one solute, passive transport down its electrochemical gradient with reversible direction of transport
outline GLUT uniporter
transports glucose down the concentration gradient, can work in either direction of in or out of the cell
is active transport with or against the electrochemical gradient
against
for the gradient driven pumps, the first solute is ____ its gradient (for free energy) and the second is ______ its gradient
down, against
differ between symport and antiport
symports are two solutes moved in the same direction and antiports are two solutes moved in opposite directions (but the [c] of both in and out are the same)
outline the NaH exchanger (antiport) example
- cytosolic pH must be regulated for optimal enzyme function
- excess H+ in the cytosol from acid forming reactions and leaks from lysosome
- transporters maintain cytosolic pH through the NaH exchanger (plasma membrane) with a sensing domain to sense pH and has H+ transported out against its electrochemical gradient
- Na+ is transported down its electrochemical gradient and provides energy
outline the Na Glucose symporter example
- Na+ is transported down its electrochemical gradient and provides energy
- glucose moves against concentration gradient
- random oscillations between conformations, reversible
- conformational changes only occur after: both sites occupied with cooperative binding of Na and Glucose, both sites empty where the molecules both dissociated
- sodium will randomly bind but transporter won’t close until glucose
how is the Na+ electrochemical gradient maintained in animal cells
through the NaK pump (plasma membrane atp driven pump)
list the 3 types of atp driven pumps
- proton type pump
- abc transporter
- v type proton pump
state two examples of how transport proteins regulate critical cellular processes
- transcellular transport of glucose
- generation of membrane potentials
what is the name of the basal + lateral domain
basolateral domain
describe the process of how transporters work together to transfer glucose from the intestine to the blood stream
- glucose actively taken up from the gut from the gut lumen through the apical domain
- active transport of the na-glucose symporter
- passive transport of glucose down the [c] gradient whilst there is a NaK pump to set up the gradient – where glucose is passively reelased for use by other tissues
in the parts of the intestinal lining do the following have low or high glucose concentrations:
- inside the lumen of the intestine
- cytosol of the epithelial cell
- extracellular fluid on the basolateral side of the epithelial cell
low
- inside the lumen of the intestine
- extracellular fluid on the basolateral side of the epithelial cell
high
- cytosol of the epithelial cell
which transport process is in the apical membrane and which are in the basolateral plasma membrane
apical: Na glucose symporter
basolateral: glut2 uniporter, nak pump
in the epithelial cells of the intestine, transport proteins are restricted by _________ _________ to seal it off so nothing can get by
tight junctions
define membrane potential
difference in electrical charge on two sides of the membrane (about hte ions)
why is the membrane potential important
used by gradient driven pumps to carry out active transport and electrical signalling (membrane depolarization)
list the two methods of generating membrane potentials in animal cells
K leak channels and naK pumps
is the flow of k leak channels in or out and what type of transport along what gradient
outward flow of K+ through passive transport down the electrochemical gradient
describe the NaK pump in membrane potential
- ~10% of membrane potential
- maintains the na+ gradient w low cytosolic [na+] and k+ gradient w high cytosolic [k+]
- electrogenic: 3 na out 2 K in, so net 1+ ion pumped out
what does it mean for membrane potential to be electrogenic
3 na out and 2 k in, Electrogenic bc extra ion pumped out = membrane potential w slight excess of positively charged ions on the outside
can cells generally balance electrical charges inside and outside of cell
yes
what is the net result of the generation of membrane potential in animal cells
a bit more + on outside (na, k), a but more - on inside (cl- and fixed anions (nucleic acids, proteins, cell metabolites))
what is the equilibrium or resting membrane potential
vary from -20 mV to -200 mV
why is resting membrane potential in - (minus)
bc it refers to whats going on in the cytosol
describe the generation of membrane potential in plants cells
with the plasma membrane p type pump: h+ pump which generated an h+ electrochemical gradient of -230 to -160 mV
- used by gradient driven pumps to carry out active transport eg the h+ driven symport, electrical signalling, pH regulation
describe p type pumps
uses atp, phosphorylated during pumping cycle, many p type pumps which transports ions, eg flippases which transports phospholipids (Maintains the asymmetry, uses AP hydrolysis in order to have moved the phospholipids to the cytosolic leaflet in golgi) and the NaK pump
go through the pumping cycle of the Na-K pump
3 na binds, pump phosphorylates itself and hydrolizes atp, phosphorylation triggers conformation change and na is ejected, 2 k binds, pump dephosphorylates itself, pump returns to original conformation and 2k is ejected into the cytosol
outline the function of the abc transporter
it is a type of atp driven pump. it uses 2 atp to pump small molecules across cell membranes.
Eg known for transporting toxins out of the cell - mech for cancer cells to gain resistance to chemo drugs is to have a lot of ABC transporters
outline the v type proton pump
a type of atp driven pumps. it uses atp to pump h+ into organelles to acidify the lumen in lysosome, plant vacuole – DOES NOT BECOME PHOSPHORYLATED
whats the difference between f and v types (proton pump and atp synthase)
f is structurally related to v type proton pump but opposite modes of action. it makes atp instead. uses h gradient to drive the synthesis of atp. present in mitochondria, chloroplasts, bacteria
is f type atp synthase reversible
yes, it depends on atp concentration and h electrochemical gradient
