Bio 1350 lecture 8: transport across cell membranes

what two factors do channels discriminate based on?

size and charge

what do transporters discriminate based on?

direct binding

what is the electrochemical gradient in a charged molecule?

a combination of the voltage gradient and the concentration gradient

what charge does the outside of the cell tend to have?

positive

what charge does the inside of the cell tend to have?

negative

what is electrochemical gradient for an uncharged molecule?

membrane potential is not relevant so the electrochemical gradient is equal to the concentration gradient

is energy required for active transport?

yes, if molecules are moving against their electrochemical gradient

what type of transport do channels mediate?

passive

what type of transport do transporters mediate?

active and passive

do channels open and close?

yes

what are gated channels?

gated channels are channels that respond to different types of simuli

does the glucose transporter facilitate active or passive transport?

passive

why did cells evolve transporters rather than channels for molecules such as glucose?

most channels are for ions which are small. Glucose is much larger and would require a large channel opening which would probably be less selective

what happens right after Na+ binds to the Na-K pump?

the pump phosphorylates itself

what happens right after the Na-K pump has been phosphorylated?

the 3 sodiums are diffused out

what happens when sodium has been diffused out?

K+ binds

what happens shortly after K+ binds?

the pump is dephosphorylated

what happens after the pump is dephosphorylated?

the pump returns to its original shape and K is ejected

symport

moves two solutes in the same direction

antiport

moves two molecules in two different directions

what does a uniport do?

moves one molecule in one direction

are symports and antiports active or passive?

mostly active but some can be passive

on which side does the ATP bind to the na-K pump?

cytosolic side