exam 3 membrane channels and transporters Flashcards
what does movement of ions and small molecules across membranes require
the use of channel and transporter proteins
what does passive transport involve
the movement of a solute down its concentration gradient - does not require energy input
what is active transport
the movement of a solute up a concentration gradient - requires energy input
where can energy come from
ATP, the movement of something down a gradient, or from high energy electrons
what are molecular pumps
the transporters involved in active transport
what type of barriers are biological membranes
semipermeable barriers
what molecules can/can’t cross membranes freely
nonpolar molecules can diffuse freely, but polar/charged solutes are unable to cross without assistance
what do transmembrane proteins channels and transporters allow
allow polar/charged solutes to cross membranes
what do channels do
allow diffusion down a concentration gradient when channel is open
what do transporters do
use conformational changes to move substances across the membrane and may transport down (passive transport) or up (active transport) a concentration gradient
what is diffusion
movement of charged solute down a concentration gradient
what is a concentration gradient
difference in concentration of a solute/solvent in one region compared to another
what does the movement of any molecule or ion moving up/down a concentration gradient require
change in free energy
what is an electrochemical gradient
sum of concentration gradient and electrical gradient
what can delta G (change in free energy) tell us
whether a substance will move passively (no energy needed) or actively (energy input required) across a membrane
what happens if delta G is negative
moves passively
delta G = max amount of energy available to drive another diffusion of solute
what happens if delta G is positive
energy required - active
delta G = the amount of energy required to move a mole of solute up its electrochemical gradient and into the cell
what is simple diffusion
diffusion across lipid bilayer (independent of proteins - no assistance needed)
what is simple diffusion limited by
polarity, charge, size
highly polar, charged, and large can’t move across membrane
what is permeability
the ability of the membrane to maintain concentration differences between the internal and external environments
what are transport proteins
proteins that move small molecules and ions across membranes
what is the difference between simple and transporter-mediated diffusion
simple is in either direction and can NOT be saturated
transporter is directional and saturable
are transporters and channels active or passive
channels are always passive
transporters can be passive or active (active are pumps)
what are ion channels
move ions and water across membrane
what is a channel
protein across membrane that allows the net flux of specific ions across a membrane down their electrochemical gradients only
what is the difference between channels and transporters
channels do NOT need to change their conformation to move each ion across the membrane (can maintain solute fluxes)
what is the structure of channels
one or more membrane-spanning protein subunits surrounding a central pore lined with hydrophilic R groups
how are ion channels highly selective
most allow only one type of ion to pass through
where does ion selectivity occur
the pore consists of a double funnel with wide openings at the surfaces of the membrane and a narrow region further in the lipid bilayer
what are ion channels regulated by
a central pore that can be gated open and shut by conformational changes
what can changes in conformation be driven by (channels)
- ligand-gated channels: the binding of ligands to the channel
- voltage-gated channels: changes in membrane potential
- mechanosensitive channels: distortion of the bilayer
- temperature-sensitive channels: temp
what is active transport
movement of solutes up their electrochemical gradients
what can active transport create and maintain
concentration gradients of solutes across membranes
how can active transport directly contribute to membrane potentials
if the transported solutes carry a net charge across the membrane
what are the three types of active transport
ATP-ase pumps, pumps that use diverse energy sources, coupled transporters
what are ATP-ase pumps
pumps that use ATP hydrolysis to move solute
what are coupled transporter
link the movement of one solute up its electrochemmical gradient to the movement of another solute down its electrochemical gradient. their energy source is an existing electrochemical gradient
what are the three classes of ATP pumps
P-type pump, F/V-type pumps, and ABC transportres
what are P-type pumps
when it hydrolyzes ATP, it phosphorylzes the pump itself, causing conformation change to allow an ion to be pumped across membrane (phorphorylation-dephosphorylation cycle to allow cycle to happen)
each pump only pumps one type of ion
what are F/V-type pumps
sam machinery as P-type, but running in different directions
what are ABC transporters
ATP-Binding-Cassette:
instead of rotary motion, ATP binds to symmetric dimers where each one binds two molecules of ATP at same time, ATP hydrolysis causes opening and closing, pushing a proton up its gradient
what does the P-type pump, calcium ATPase do
allows cell to detect small increase of calcium (can be used as signaling molecule)
where are calcium ATPase pumps found
in ER and surface of cell - direction flows out of cytosol into other compartment
what happens for every ATP molecule hydrolyzed with Calcium ATP-ase
can move one calcium ion - helps maintain low resting calcium concentration in cytosol
what does the P-type pump, Na+/K+ pump do
it’s an antiporter - for each cycle, it transports 3 Na+ out of a cell and 2 K+ into a cell (net charge of +1 out of the cell per cycle)
how does the Na+/K+ pump work
it has specific binding sites for Na and K - each step in hydrolysis of ATP and binding of transported ion drives conformational chanes
what is the F-type pump
uses a proton gradient to generate ATP - found in mitochondria and thylakoid membrane of chloroplast and in bacteria
what is the V-type pump
regulates pH of environment by pumping H+ into lysosomes, synaptic vesicles, and plant vacuoles
how is V-type pump different than F-pump
V-type energy causes rotary motion, moving proton across membrane - F-type is reverse and is converted into ATP synthesis
what does a bacterial ABC transporter do
transports nutrients into cell and binds to ATP causing a conformational change - then is hydrolyzed and released, opening transporter
what does a eukaryotic ABC transporter do
exports substances out of cells - works like bacterial, but in opposite direction
what do MDR proteins do
multi-drug resistance proteins - expel toxic substances from cell (overexpressed in cancer cells to resist therapeutics)
