transport across membranes Flashcards
phospholipid bilayer is made up of..
one glycerol molecule attached to two fatty acid tails and a phosphate group. phosphate head is polar forming the hydrophilic head and the fatty acid tails form the hydrophobic region. Tails face each other, away from the water in cytoplasm and extracelluar fluid, forming a bilayer.
what forms the fluid part of the cell membrane
movement of phospholipid bilayer
what forms the mosaic part of the cell membrane
uneven distribution of proteins
what does cholesterol do
decreases permeability of the membrane and increases the stability, more cholesterol=less fluidity of membrane
what are channel proteins?
-pores within the membrane
-only allow specific charged ions and small molecules to move across by facilitated diffusion
-specific complementary molecules can pass through specific channel proteins
carrier proteins
transport complementary charged/large molecules by facilitated diffusion and active transport
role of receptor proteins?
act as receptors for specific complementary molecules
glycoproteins
composed of carbohydrates and proteins. important in cell recognition and act as antigens
immune cells detect the specific shape of glycoproteins and recognise them as self
produced in the golgi-body
what are aquaporins?
channel proteins specific to water
what is diffusion?
net movement of molecules from an area of higher concentration to an area of lower concentration across a partially-permeable membrane
what type of process is diffusion?
passive-it does not require energy(ATP)
what type of molecules can pass through the cell membrane via diffusion?
non-polar, small, lipid-soluble molecules
fick’s law
RATE OF DIFFUSION=S.A X CONCENTRATION GRADIENT/DIFFUSION DISTANCE
what is facilitated diffusion?
water-soluble , large or charged molecules pass through the cell membrane via channel or carrier proteins. they only transport complementary molecules
what is osmosis?
net movement of water molecules from a higher water potential to a solution with lower water potential through a selectively permeable membrane
highest water potential
0kPa
what lowers the water potential
addition of solute
what is water potential
free moving water molecules collide with the surface of the membrane and exert pressure , known as water potential
what happens if water potential is higher outside the cell
water moves in via osmosis
animal cells swell and burst(lysis)
plant cells increase in mass and become turgid(cell wall prevents lysis)
what happens if water potential is lower outside the cell
water moves out of the cell via osmosis
animal cells shrivel (crenatation)
plant cell membrane pulls away from the cell wall and become plasmolysed
what is active transport?
net movement of molecules across a membrane from an area of lower concentration to an area of higher concentration using carrier proteins (and energy/ATP)
how does the carrier protein transport the molecule?
molecule binds to the binding site of the carrier protein
hydrolysis of ATP releases energy and phosphorylates the protein
this causes the protein to change shape and transport the molecule across the membrane
give an example of where exocytosis is used
to move enzymes and glycoproteins from the golgi apparatus to the cell surface membrane to secrete proteins
exocytosis
ATP is required to move the vesicle to the cell membrane, it then fuses with the cell membrane and molecules are released
