1.4 Membrane transport Flashcards
what is endocytosis and how does it use vesicles?
because the membrane of cells is so fluid materialas can be taken in by small sacs of membranes called vesicles whcih have a droplet of fluid inside and are spherical and are present in eukaryotic cells.
A small region of the membrane is pulled in and pinched off. Proteins in the membrane do this using ATP
vesicles in endocytosis have water and solutes from outside the cell and also larger molecules that cannot pass across the plasma membrane.
- e.g. in placenta proteins from the mothers blood e.g. antibodies
- amoeba and paramecium take in undigested food
- white blood cells in response to infectio n
example of where vesicles are used for movement within cells
protein synthesized in ribosomes or rER accumulate and vesicels bud off and move them to golgi and from there to the plasma membrane to be secreted (or lysosomes)
in growing cells plasma membrane needs to increase so phospholipids are synthesized and are inserted into rER membrane and then vesicles move and fuse with plasma membrane
–> also used to increase surface area of organelles
what is exocytosis?
vesicels are used to release materials from the cell
e.g. digestive enzymes are released from glands by exocytosis
can be used to expel waste products or unwanted materials e.g. in paramecium use a contractile vacuole to expell water
what is simple diffusion?
the spreading out of particals in liquid or gas that happens because the particles are in a constant random motion. More particles move from high to low conc down the concentration gradient (net movement)
PASSIVE PROCESS - no energy
across membrane need to pass through phospholipid bilayer (so be permeable to this)
NOT polar particles (unless only partial charge on surface or very samll such as urea of ethanol)
E.G. lipid based steroids can pass through hydrophobic region
what is facilitated diffusion?
particles which cannot diffuse across the phospholipids bilayer need channels - holes with narrow diameter and walls made of proteins NARROW SELECTIVE PROTEIN CHANNEL
diameter and type of proteins affect properties and the type of molecule that can pass through
cells which can control what type of channels it has can therefore control what substances diffuse in and out
what is osmosis?
due to the differences of concentration of solutes dissolved in water either side of the cell. the dissolved substances form intermolecular bonds with water thus restricting its motion.
Higher conc - less water free to move - net movement will be to higher conc
PASSIVE
water hydrophilic but can pass thorugh phospholipid bilayer. some cells have aquaporins (water channels) e.g. kidney cells and root hair cells
aquaporins narrow point so one water molecule at a time. positive charges at most narrow point so H+ ion cannot pass
what is active transport?
needs energy atp
carried out by globular porteins in membrane called protein pumps.
partical enter pump and reaches central chamber where a conformational change to the protein means protein can pass to opposite side and pump return to normal
preventing osmosis in excised tissues and organs
high osmolarity solutions - hypertonic - watee leaves cell
–> as cytoplasm shrinks and plasma membrane stays teh same you get indentations or crenellations
low osmolarity - hypotonic - water enters cell
–> cells burst leaving red cell ghosts
ISOTONIC same osmolarity
in medicine isotonic sodium chloride solution (saline) osmolarity of 300 mOsm (milliOsmoles)
saline used for
- intravenous drip - into blood stream
- rinse wounds and skin abrasions
- keep areas of damaged skin moist for skin grafts
- basis for eye drops
- frozen to slush for packing organs
hypotonic- names - hypertonic
lysis/swells -animals cells - shrivelled/crenated
turgid-flaccis-plant-plasmolysed
active transport of sodium and potassium in axons why?
an axon is a nerons and has a tubular membrane with cytoplasm. convey messages rapidly in an electrical impulse
nerve impulse is rapid movement of sodium and potassium ions across axon membranes by facilitated diffusion - due to concentration gradient which is established by active transport - hence need sodium and potassium pump
how does the NA and K pump work
pumps has cycle 3 NA ions out of axon and 2 K ions into axon needs 1x ATP
- interior pump opens to inside axon nand 3 NA ions enter and attach to binding site
- ATP transferes phosphate group to pump so pump changes shape and interior is closed
- interior pump opents to outside axon and release NA
- 2 K ions attach to binding site
- binding of potassium causes phopshate gorup to relase so pump cahnegs shape so again only open to inside of axonm
- interior of pump opens and 2 K ions release then repeats
facillitated diffusion of potassium in axons how does it work
potassium chaneels have 4 protein subunits and a narrow pore between so potassium can go either way (0.3 nm at narrowest point)
K ions smaller than this but dissolve and become bonded to water so need to break bonds from water to pass through so you get temporary bonds between ion and amino acids in narrowest part of pore. after this part the ion again becomes assosciated with a shell of water molecules
otehr ions are too large or too small to bond with amino acids so only K can pass
how does voltage tie into potassium channels
potassium channels are voltage gates - due to an imbalance of negative and positive charge across membrane
+ outside and - inside means closed channel
+ inside and - outside means channel open
then channel closed rapidyl due to an extra globular protein subunit or ball attacehd by a flexible chain of amino acid which fits inisde the open pore milliseconds after the pore opens
stays there until pore closes
