Exam 1: Membrane Transport

key trait of the plasma membrane

selective permeability

categories of membrane transport

passive and active

passive transport

no ATP required (kayaking downstream)

high to low concentration (DOWN the gradient)

simple diffusion, facilitated diffusion, and osmosis

active transport

ATP required (kayaking upstream)

low to high concentration (AGAINST the gradient)

protein/ion pumps or bulk transport (vesicles)

diffusion vs. osmosis

diffusion = movement of solutes

osmosis = movement of solvent (water)

what drives the movement of solutes during diffusion

the concentration gradient - high concentration in one area vs. low concentration in another

simple diffusion

a type of passive transport that does not need the help of membrane proteins

going from high to low concentration

what molecules can do simple diffusion and why

nonpolar (hydrophobic) - because the majority of the membrane is the hydrophobic lipid tails

very small polar molecules (water) - occurs slower because it takes longer to pass through the lipids

speed of simple diffusion

small molecules will diffuse faster than large ones

nonpolar will diffuse faster than polar

facilitated diffusion

a type of passive transport that is assisted by a membrane protein (channel or carrier)

going from high to low concentration

channel proteins in facilitated diffusion

a tunnel for the molecules to go through

carrier proteins in facilitated diffusion

opens one side, recognizes the molecule, and opens to the other side to let it pass through

what molecules can do facilitated diffusion

larger polar and strongly charged molecules

water also can go through aquaporins (specialized membrane proteins)

why does facilitated diffusion take time

there are a limited amount of membrane proteins that these molecules can use to pass through

factors that increase speed of diffusion

increased temperature

larger difference in concentration gradient

factors that decrease speed of diffusion

distance for the molecule to travel (membrane thickness)

larger molecular size

osmosis

a type of passive transport

the diffusion of water across a semipermeable membrane from area of high water (less solute) to low water (more solute)

why does active transport require ATP

because it takes energy to paddle upstream (against the concentration gradient) or form the vesicles

protein pumps or ion pumps

moves solutes against their gradients

splits ATP molecules to release energy to push the molecules

sodium-potassium pump

3 Na+ out for 2 K+ in

how our nervous system sends electrical signals throughout our body

bulk transport

receives or releases large amounts of molecules at once from low concentration to high concentration via vesicles and vacuoles

vesicles have their own lipid bilayers that allow them to fuse with the cell membrane

exocytosis

exit the cell

endocytosis

enter the cell