L4 Flashcards
describe the proteins in protein mediated membrane transport
what do they function as
the span the cell membrane (all the way through)
they function as enzymes as they catalyse the transport of solutes across the membrane
in passive transport proteins function as….
channels or carriers
passive transport happens through…..
facilitated diffusion and therefore is concentration dependent (high to low)
what are the 2 generalised forms of active transport
primary (ATP dependent) and secondary active transport
what is secondary active transport
these proteins act as carriers/transporters and they use the down hill gradient of one solute to transport another solute up its concentration graident
how selective are the channels and carriers in passive transport
they cover a wide range of selectivity (eg K+ channels are very selective whereas Na+ channels are not)
why are the proteins in passive transport selective
because they require an interaction between the substrate and the protein. these proteins also often have a binding site/selectivity filter for that specific solute
in passive transport what is the difference between channels and carriers
channels are fast as they usually have a gate and when that gate opens the thing that it is selective for will rush through it
carriers are much slower because they require an interaction and a conformational change of the bratein
what is a pore
in is the simplest form of a channel
they are a small selective tunnels through which molecules can move rapidly
what do pores typically transport
ions, water (eg aquaporins), small solutes
what are channels
they are gated pores that open and close spontaneously
pores are a passive mechanism. what does this mean
movement of a solute via a channel is determined by the greadent for the solute
this is both the electrical and chemical greadent (electrochemical)
what are the 3 ways that a channel could be named
the obvious way (what it is/descriptive way)
after the diseased state
or after the thing that inhibits it
when facilitated diffusion occurs it happens through a gated channel. is this all or nothing
yes
what is CFTR
cystic fibrosis transmembrane regulatory protein
it is a Cl- channel (note that this is not a regulatory protein)
CFTR is a Cl- channel but it can also let through something else. why is this
it can also let through bicarbonate
this only will happen when bicarbonate is in high concentration
this doesn’t really happen in the body as cells which have CFTR always make sure they have a high concentration of Cl
when it does get in, it does slightly reduce the efficiency for that specific protein but it will have very little overall effect
what is the permeability of a membrane to a solute determined by
the number of channels for that solute in the membrane
and
the open probability of the channels in the membrane
the fraction of time ligand gated channels stay open/the number of channels is modified by….
ACh and other specific molecules
the fraction of time voltage gated channels stay open/the number of channels is modified by….
in the case of membrane potential it is voltage gated Na channels
the fraction of time mechanical gated channels stay open/the number of channels is modified by….
mechanical deformation
eg touch receptors and hair cells
what is cotransport
when both solutes move in the same direction
also called uniport
what is counter transport
when solutes move in the opposite direction
what does carrier mediated transport usually transport
ions (Na, K, Cl, HCO3)
other solutes like glucose and amino acids
what determines selectivity in carrier mediated transport
binding sites
describe the binding sites for protein in carrier mediated transport
it is a turnstyle type system (things at theme parks that only let one person through at a time)
the binding site/s is only accessible from one side of the membrane at a time
it will bind one or 2 molecules and then changes conformation, transporting solute across the membrane
what is carrier inhibition
2 reasons
carriers are conducts that are gated by 2 doors that are never open at the same time.
if something were to bind and keep the carrier in an open form that is a inhibitor
it can also be if something with similar characteristics as the selected solute is in a high concentration that that will bind reducing the efficiency of the carrier
lol
lol
how are carriers defined
in therm of their slute
this could be the solute transported against the electrochemical greident or the binding of the substrates required
what are some examples of carriers in primary active transport
Na/K ATPase
H/K ATPase
what are some examples of carriers in secondary active transport
SGLT1 (sodium-glucose linked transporter 1)
NHE (NA H exchanger)
AE (Cl -HCO3 exchanger)
anion exchangers
what is the rule for how secondary active transporters work
the downhill transport of one solute drives the uphill transport of a second solute
cells with CFTR need to have a high intracellular conc of Cl. how do they maintain this
cells with CFTR also have K+ channel, a NaK ATPase and NKCC1
NKCC1 brings Na, Cl and K+ into the cell.
we can’t have a high conc of Na inside the cell otherwise it will burst so Na/K ATPase pumps 3Na out and 2K in
this extra K+ brought in by the Na/K ATPase and NKCC1 is then pumped out of the cell
what is NKCC1
Na+ K+ Cl- cotransporter
it requires Na as it used the energy of Na moving down it greadent to being K and CL into the cell
what does CFTR do
it transports Cl- into the lumen
without this your gut and lungs would dry up
describe the K+ channel in cells with CFTR
it is a uniporter as it recycles K+ into the serosa
