week 10 Flashcards
what are the three main classes of membrane proteins that transport molecules and ions across cellular membranes
- channels
- transporters
- atp powered pump
channels
ions and hydrophilic molecules can flow down their concentration gradient. can be non gated or gated
transporters
include uriporters, symporters and antipoerters that have one molecule moving down the gradient (at least)
cotransporters
sympeorters and antiporters that move another molecule against its gradient.
facilitated transporers
- channels and transportersa
tp powered pumps
energy from atp hydro to move a variety of ions and small molecules against concentration gradient
facilitated transporters
include channels, gates and transporters, the driving force being concentration gradients, specific to certain molecules
- hydrophilic substances are moved through a protein lined pathway so that there is no contact with the hydrophobic interior of the membrane.
- faster than if they are to use passive diffusion
- saturable meaning that at some point they can reach the max of how much can get through at a given time
-
is atp required for facilitated transport
- no but it might be required to set up concentration gradient
example of an open channel;
the potassium resting channel
is channel opening/closing based on ligand binding?
no, due to chemical or electrical signals
voltage gated channel
depends on the charge across the plasma membrane
- e.g. SR calcium release channel.S
SR calcium release channe
- when muscle contraction occurs, there is a lot of calcium please
- electrical charge from the nerve down to the t tubule
- hits teh voltage gated channel that opens and releases caclm
- ## ca flows out of the channel and can be pumped back in
specificity of channes
- integral membrane proteins can create holes in membrane large enough for solutes to pass throughsi
size based exclusion in facilitated transport change;l
- having size-based exclusion
- specificity can lead to membrane potential
- what is meant by size-based exclusion- hydrophilic interior to channel
- ae abc class pumps for big or small molecules
K+ resting channel, size selectivity
- only potassium interacts oropperoly with the polar amino ids oto shed its hdyration shell and pass through the channe’l, needs the right energy to get rid of the water , and the oxygens in teh channel prove it the same energy
- Na in potassium pore is too small to interact with he all the oxygen that are spaced specifically for K,
how does speciciicty/size based exclusion lead to creation of electric potential
- K+ resting channel only allows potassium, not Na or Cl to pass0 when K flows down the concentration gradient, a negative charge is left on teh side that it leaves
- this leads to all cells having a negative charge on the inside of the PM
transporters
are normally closed, requires ligand binding to open, in this case the ligand is the molecule that is being transported. this involves significant conformation changes.
- not an “open” channel
uniporters
- ## open and close in response to a ligand
WHAT IS glut 1 transporter
- it is a glucose transporter that has high affinity glucose binding sites, driving force is concentration gradient of glucose
- a uniporter specific to glucose
active transport
- pumping molecules against concentration gradient using ATP
- are considered pumps
V class pumps
H+ only
- important for lysosome acidity, pump protons from cytosolic to exoplasmic side (pumping out of cell)
F class
H+ only, in mito and chloroplasts, pump protons from exopalsmic to cytolsic side, e.g atp syntheses
P class pumps
H+, Na+. K+, or Ca2+
ABC class pumps
- are used to export ions, sugars, amino acids, peptides, proteins phosplipipds, cholesterol , toxin , foreign substances
- some are able to flip components from one membrane leaflet to another
ion concentrations in a cell
- high Ca outside
- high K inside
- high Na outside
- these are the directions in which these ions are pumped
Muscle Calcium ATPase, a
- an example of a P class pump
- sits on the SR
- using atp hydrolysis to pump ca out of cytoplasm into the SR
- ## voltage gated channel releases calcium and allows muscle ATPase to pump calcium back into SR
Na/K P class pump***
- K+ resting channel allows K outside of cell, most cells have negative charge on the plasma memvrane
- atp is used to pump 3 sodium out and 2 potassium in per ATP
- end up with high concentration of sodium outside of cell
secondary active transport (xo transport)
by antiports and symports
- coupled transport between two different molecules
one is with the gradient, one is against
how does secondary active transport work
- ion gradients generated by atp powered pumps
- fre energy associated with these ions going back along concentration gradient is coupled with the import or export of other molecules against their concentration gradient
