Active transport/Exo and endocytosis Flashcards
another name for protein pumps
carrier proteins
how does active transport via protein pumps work?
The solute enters the pump and E from ATP changes the pump’s conformation so that the opening is on the other side of the plasma membrane. The pump goes back to its initial conformation spontaneously (no ATP required).
what is the polarity of the membrane and what is its value for neurons?
it si the difference between the charges of the outside and the outside of the cell - for the neuron it is -70 mV because the outside is more positive than the inside for 70 mV
why is the inside less positive than the outside of the neuron?
there is more K+ inside the cell and more Na+ outisde the cell - but there is slightly more Na+ than K+
when is the membrane polarity 0 mV?
when the cell is dead
why is the membrane polarity 0 mV when the cell is dead?
because the Na+ and K+ channels are always slightly open so the ions leak down their concentration gradients - this is why Na+/K+ pump occasionally pumps them inside - to maintain the uneven distribution of the charges - when the cell is dead there is no ATP to power the pump
what happens when Na+ and K+ leak down the channels?
polarity of the membrane dissipates
resting potential - what is it and the value
when at rest the plasma membrane has an unequal distribution of charges on its opposite sides (it is electrically polarized) - 70 mV
action potential
once the stimulus is applied the Na+ channels open completely and the ions diffuse through them - Na+ goes into the cell, making the inside of the cell more positive - 40 mV
nerve impulse
change of polarity of the membrane
depolarization
turns resting potential into action potential (membrane becomes plus charged)
repolarization
when K+ channels open and K+ diffuses out of the cell - Na+ and K+ have now switched places so the Na+/K+ pump has to get them back to initial state
endocytosis/exocytosis
Active transport of large particles or entire cells across the membrane by means of vesicles. Vesicles can also transport materials within a cell, between rER, sER, GB, and the plasma membrane.
The fluidity of the membrane allows it to…
change shape, break and reform during endo and exocytosis.
Endocytosis
- vesicle is transported by being engulfed by the plasma membrane
- substances from outside enter by a vesicle into the cytoplasm
where are the substances engulfed by the cell transported and why?
The vesicles move through the cytoplasm and fuse with lysosomes and their enzymes digest the engulfed substances.
what is transported by exocytosis
undigested components
example of freshwater and ocean fish
fresh/ocean:
- hypotonic/hypertonic env.
- water movement into/out the body
- large/small V of urine
- diluted/concenrated urine
- active transport of ions into/out the body
- doesn’t drink/drinks water
the Na/K pump transports Na and K in the opposite direction so it is…
an antiporter/exchange transporter
what is indirect active transport
example of sodium-glucose cotransporters (membrane proteins) that move Na and glucose together into the cell - Na moves down its concentration gradient, releasing ATP - glucose moves against its C gradient and uses ATP released from Na diffusion (this transport depends on the Na pump to pump Na back out to maintain the C gradient)
example: reabsorption of glucose by kidneys, absorption of glucose from digested foods by the small intestine epithelial cells
