move across bilayer from high to low concentration to reach equilibrium.
Facilitated Diffusion (Passive Transport)
dolecules will spontaneously flow "down hill" from a region of high concetration to low. they dont need no other driving force.
Protein mediated-carries bind to solute, channels form AQUEOUS pores (gated)
discriminate mainly on the basis of size and electric charge:if a channel is open, an ion or molecule that is small enough and carrie the appropriate charge an slip through a narrow trapdoor.
allows pasage only to those molecule or ions that fit into a binding site on the protein; it then transfer these molecules across the membrane one at a time by changing its own conformation, acting more like a turnstile than an open door.
bind solute on one side of and release the other requires concentration gradient, no net transfer
gate is controlled by the membrane potential. Major role in controlling signals to nerve cells,
controlled by the binding of some molecule(the ligand) to the channel extra cellular or intracelluar
opening is controlled by the binding by a mechanical force applied to the channel. example: you ear using auditory hair cells which use vibrations to pull the channels open causing ions to flow into the hair cells.
a fine glass tube that used a microelectrode to isolate and make electrical contact with a small area of the membrane at the surface of the cell. this technique make it possible to record the activity of ion channels in all sorts of cell types.
transport solute against the concentration gradient and establish ion gradients
the downhill movement of the first solute down its gradient provides the energy to drive the uphill transport of the second.
ATP driven pump
a pump that hydrolyze ATP to ADP to transport NA+ out of the cell