transport-1 Flashcards
how do concentration gradients work
lead to solute transport predominantly towards the area of lower concentration (approaching equilibrium)
what happens if a charge separation exists across a membrane
it will create a transmembrane potential
what will create a transmembrane potential
if a charge separation exists across a membrane
what is an electrochemical gradient (what creates it)
combination of concentration and charge gradient
where will charged particles tend to move with electrical gradients
charged particles will move into the region of opposite charge
what does the C2 mean in
โ๐ฎ๐ป = ๐๐ ๐ฅ๐ง ๐ช๐ / ๐ช๐
+ ๐๐๐ซ๐
[A] destination
what does the C1 mean in
โ๐ฎ๐ป = ๐๐ ๐ฅ๐ง ๐ช๐ / ๐ช๐
+ ๐๐๐ซ๐
[A] origination
what does the Z mean in
โ๐ฎ๐ป = ๐๐ ๐ฅ๐ง ๐ช๐ / ๐ช๐
+ ๐๐๐ซ๐
ionic charge
what does the F mean in
โ๐ฎ๐ป = ๐๐ ๐ฅ๐ง ๐ช๐ / ๐ช๐
+ ๐๐๐ซ๐
faraday constant
what does the ๐ซ๐ mean in
โ๐ฎ๐ป = ๐๐ ๐ฅ๐ง ๐ช๐ / ๐ช๐
+ ๐๐๐ซ๐
membrane potential (usually -50mV)
do the calculation in the notes
okay
what does rate/kinetics across the membrane depend on
concentration of the molecules being transported and the nature of the transport process
how do small non polar molecules move across the membrane
diffuse freely (simple diffusion)
what do ionophores and channels do (simple)
allow molecules to move depending on concentration gradients
what do carriers do and what does the rate depend on
move molecules with a rate determined by both the gradients involved and the transporter kinetics (active and passive transporters)
what are the 2 main transporter types
passive and active
what do passive transporters do (what determines solute movement)
solute movement is determined by electrochemical gradient
what is the free energy of passive transporters
less than zero
what direction of movement happens with active transporters
movement of solute against the gradient
what is required in active transporters
energy input (coupled to exergonic process)
what is primary active transporter
exergonic chemical reaction
what is secondary active transporter
exergonic solute/ ion transport
what is the deltaG for active transport
less than zero
what is the deltaG solute/ion transport for secondary active transport
more than zero (its going against gradient)
what is the deltaG for other molecule secondary active transport
less than zero
what determines solute movement in passive transport
electrochemical gradient
what is delta GT for passive transport for the solute
less than zero for the solute
is passive transport specific
may be specific or non specific dependent on transport structure
what ultimately dictates direction of passive transport
solute
what ultimately dictates specificity of passive transport
transporter
what are ionophores
molecules that shuttle ions across membranes down their concentration gradient
what are 2 types of ionophores
carrier and channel
what are carrier ionophores like
they are undergoing motion back and force across membrane like a raft or ferry
what are channel ionophores like
more like tunnel or a bridge, create opening from one side to another
what are many ionophores like + how are they made
peptide or peptide like molecules produced by microorganisms
what do ionophores do to trans-membrane electrochemical gradients + what does this cause
it will destroy them, affecting secondary active transport processes
what do ionophores do to secondary active transport processes + why
affect them because it will destroy trans-membrane electrochemical gradients
what class is valinomycin
a carrier ionophore
what is valinomycin made from
neutral peptide-derived carrier ionophore
what does valinomycin do (what is the mechanism)
six carbonyl groups will form a stable interaction with K+ ions
moves across the membrane
what does valinomycin do as an ionophore (how does it work)
lipid-soluble (bound and unbound) and can move across the membrane
is valinomycin toxic
it is potentially poisonous to any cell
what does valinomycin bind
K+
how many carbonyl groups in valinomycin
6
what kind of phobicity happens with valinomycin
hydrophobic
what linkages happen in valinomycin
a mix of ester and amide linkages
what does valinomycin make coordination bonds with
water
what is gramicidin
peptide based channel ionophores
what are 3 types of gramicidin
A B C
what are gramicidins A B and C + What structure do they form
linear peptide structures that form a beta helix structure
what is the secondary structure like in gramicidin and why
beta-helix- unusual structure because of alternating L and D amino acids
what creates the membrane-spanning channel in gramicidin
dimer
what kind of ionophore is gramicidin (what cations)
monovalent cation ionophore (K+>Na+) -specific
what is the primary structure of gramicidin
alternating L and D amino acids
where do the side chains of gramicidin point
away from the helix core
what is the hydrogen bond pattern like with gramicidin
beta sheet
where do the side chains of valinomycin point
side chains point out
where are aromatice residues like in gramicidin
clustered near the interface near the polar and non polar environment
what are porins (what kind of secondary structure)
beta-barrel containing transmembrane proteins
are porins selective
may be non selective (except for size) or selective for transported molecules
are porins ion specific
no
can anions go through porins
yes
what kind of symmetry in lots of porins
C3
can porins be dihedral and why
no because they usually have a very specific orientation, not like 1 up 1 down
what symmetry in maltoporin
C3
what kind of โmerโ is maltoporin
homotrimer
what kind of structure do maltoporin subunits have
18 stranded beta barrels
what are the maltoporin openings like and where
in each subunit. left-handed curvature with an arrangement of non-polar/aromatic and polar residues
what direction of beta barrel in maltoporin
anti-parallel
what kind of chains can pass through maltoporin membrane
alpha1-4 linked linear chains
why is maltoporin called a greasy slide
because there is partial hydrophobic areas
what do ion-selective channels do
allow for rapid ion movement across a membrane
what direction do ion selective channels do
down concentration gradient
what is the rate of ion selective channels
rates approach free-diffusion limits
are ion selective channels selective
highly
are ion selective channels gated
they may be (opened or closed)
what is a selectivity filter / what is it / how
channel functional groups that arrange to interact with very specific molecules
what does selectivity filter determine
channel selectivity
do ion selective channels change shape when things go through
no
is there an upper limit with ion selective channels
no, its like free diffusion, no Vmax
how many subunits in K+ channel in S. lividans
4
what kind of symmetry in K+ channel in S. lividans
C4
how many helices in K+ channel in S. lividans
2 transmembrane helices + additional alpha helix in core
where is the K+ channel formed in K+ channel in S. lividans
between subunits - single channel passes from one side to the other of the bilayer
where do K+ binding sites occur in K+ channel in S. lividans
series of K+ binding sites exist along the interface
where is the selectivity filter in in K+ channel in S. lividans
mainly top part
what charge are the openings in K+ channel in S. lividans
negatively charged
where is the third helix in each subunits oriented in K+ channel in S. lividans
with its negative dipole towards the channel openings
how many binding sites in the K+ channel in S. lividans
4 K+ binding sites in the channel
what happens when new ions enter in K+ channel in S. lividans
the previously bound ions move further down the channel in alternating binding sites
can Na+ interact in K+ channel in S. lividans + why
no because they are too small
does the K+ channel in S. lividans change shape as K+ binds
no
