Membrane Transport

membrane is permeable to

small non polar molecules

membrane job (3)

separate cell from outside enclosure, keep cell contents tgth, creates controllable interior for cellular processes

hard for … to cross membrane

ions/charged molecules, large polar molecules

what decides membrane permeability

size, polarity, charge, functional groups, hydrophobic/hydrophilic

molecules that interact well with hydrophobic interior can

cross membrane

small non polar permeability

high

small uncharged polar permeability

some

large polar permeability

very low

ions permeability

extremely low

macromolecules permeability

extremely low

hydration shell

in water ion are surrounded by water molecules

cations attract … end of water

oxygen

anion attract … end of water

hydrogen

hydration shell makes ions

larger

hydration shell is unfavorable inside

hydrophobic bilayer

ions need … to cross

transmembrane proteins

diffusion definition and why

random net movement of molecules because of kinetic energy

net movement is the overall movement of

something in one direction after considering movement in both directions

diffusion net movement of (conc)

high to low conc

diffusion, molecules move

down conc gradient

diffusion is energetically … and increases…

favorabel and increases entropy

in diffusion, at equilibrium, conc is equal, no net movement but

molecules keep moving randomly in both directions

osmosis

net movement of water across a selectively permeable membrane

osmosis, water moves toward the side with

more solute / lower water conc

osmosis is not the diffusion of water its driven by

pressure (osmotic pressure)

hypertonic outside solute

higher

hypertonic net water moves

out of cell

hypertonic result

cell shrinks

isotonic outside solute

some

isotonic net water moves

no net movement

isotonic result

cell keeps its size

hypotonic outside solute

lower

hypotonic net water movement

into cell

hypotonic result

cell swells, may lyse(burst)

2 types of transport

active, passive

2 types of passive transport

simple, facilated diffusion

in simple diffusion, small non polar molecules

move directly though bilayer

simple diffusion requires

no membrane proteins / energy

simple diffusion, molécules move

down conc gradient

simple diffusion individual molecules keep moving

randomly in both directions even at equilibrium

facilitated diffusion is for

polar, charged, large molecules

facilitated diffusion requires

membrane protein / no energy

channel proteins provide

hydrophilic passageway ( a pore lined w polar + charged R groups)

chenille poroteins are selective (ex)

ions ( K+, Na+, Cl-, Ca 2+), small polar molecules (H20)

channel proteins usually faster than

carriers

2 types of channel proteins

leak and gated channels

leak channels are

always open

leak channels speed

slow

gated channels are open/close with

signals

gated channels speed

very fast

gated channels ex

K+ Chanels in nerve cells

carrier proteins bind

molecules nad change shape to move it across

carrier proteins require no energy, free energy …

difference between carrier’s shapes is small

why active transport

sometimes cells need o move smth against once gradient, take nutrients that are concentrated inside, remove substances that are more concentrated outside

active transport requires

energy

active transport uses

membrane transport proteins

active transport 3 types

primary, couples transports, secondary active transport

primary active transport uses

ATP directly

ATP —>

ADP + Pi

primary active transport proteins=

pumps

couples transporters

use movement of 1 substance to drive movement of another

symporters are

2 different substances that move in same direction

anthiporters are

2 different substances that move in opposite directions

in seoncdary active transport ATP is

not used

secondary active transport builds a gradient, protons are

protons are pumped across membrane with ATP

secondary active transport creates … gradient

electrochemical gradient, stores potential energy

secondary active transport uses gradient

protons flow back down their gradient, energy drives another molecule uphill