5. Introduction to membrane transport Flashcards
what is the membrane permeable to
gases
ethanol
urea and water
what is the membrane impermeable to
large uncharged molecules (glucose)
ions = K+, Mg+, Ca2+
charged polar molecules
define signal transduction
the rapid translocation of ions across a membrane which is involved in cell communication
the membrane allows compartmentalisation, what does this mean
means each organelle can have different ion concentrations and conditions
what are the three classes of transmembrane transporters
- pumps
- carriers
- channels
what are pumps used for
use ATP to pump ions against electrochemical gradients
what type of transport are pump transporters used for
primary active transport
what ions do pumps generally transport
H+ or Na+
summarise pumps:
- use ATP to pump ions against gradient
- primary active transport
- transport mainly H+ and Na+
what type of transport do carriers engage in
secondary active transport
name 3 types of carrriers
symporters
antiporters
facilitators
what do symporters do?
use driver ion electrochemical gradient to drive other solutes in the same direction
what type of transporter establishes the electrochemical gradient for driver ions
pumps
what is the difference between symporters and anti porters
in symporters - the driver ions and solutes move in the same direction
in antiporters - the driver ions and solutes move in OPPPOSITE directions
what are facilitators, what can they not be?
allow facilitated diffusion down an electrochemical gradient
- cannot be energised
what is another term for facilitator
uniporter
true or false: facilitators use driver ions? explain
false
- facilitators do not use driver ions but rather enables passive solute movement
what is the third type of transmembrane transporters
ion channels
describe ion channels
transport is passive down an electrochemical gradient
usually highy regulated - defined open and shut kinetics
selective for specific ions
give an example of an antiporter, how do they work?
sodium calcium antiporters, they remove calcium from the cytosol or sodium symporters
give an example of a channel, what is it involved in?
chloride channel
- role in osmoregulation
plant and fungal cells have a proton economy what is this
means they use protons and proton primary pumps to generate a proton electrochemical gradient
what is the Nernst equation used for
calculates the equilibrium potential
define equilibrium potential
the membrane potential required to exactly counteract the chemical forces acting to move one particular ion across the membrane
what pumps do animal cells have
sodium-potassium pump =
3 Na+ out, 2 K+ in
what is the effect of the animal sodium-potassium pump
generates a large electrochemical gradient for sodium influx
name a facilitator present in animals
glucose transporter
plant and fungal cells have hydrogen pumps, what does this do
expels 1 hydrogen ion per ATP molecule hydrolysed
what does the hydrogen pump generate
a large electrochemical gradient for H+ influx
what is the most dominant channel in plants and fungi
K+ channels
bacteria also have H+ pumps, what is the difference
rather than using energy from ATP
they act as a result of the electron transport chain
how do bacterial carriers work
exhibit coupling to the H+ influx
what is the most abundant transmembrane transporter
pumps
many more pumps than ion channels
in the end-membrane, what pump expels H+
V-type H+ pumps
from the cytosol into the endomembrane lumen
how many hydrogen molecules per ATP molecule in endomembrane H+ pump
2 H+ per ATP molecule
what are most endomembrane carriers
antiporters
what are endomembrane channels mainly involved in
membrane voltage regulation (calcium channels)
how many ions do pumps transfer per second
~100
how many ions do carriers transport per second
~1000
