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Cell Bio > Membrane Transport > Flashcards

Membrane Transport Flashcards

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1
Q

what is a key feature of the lipid bilayer

A

selectively permeable

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2
Q

what does the lipid bilayer’s selective permeability permit

A

different conc of materials in the intra and extra cellular spaces

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3
Q

what varies the permeability of smth through a membrane

A
  • size
  • charge
  • polarity
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4
Q

what is the permeability of small nonpolar molecules through the lipid bilayer

A

almost all goes through (tiny bit doesn’t)

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5
Q

what is the permeability of small uncharged polar molecules through the lipid bilayer

A

some goes through, most is bounced off

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6
Q

what is the permeability of large uncharged polar molecules through the lipid bilayer

A

most is bounces off (tiny lil bit can go through)

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7
Q

what is the permeability of ions through the lipid bilayer

A

all is bounced off (none goes through)

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8
Q

which two things cannot diffuse freely through a cell membrane

A
  • ions
  • polar molecules
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9
Q

what assists the transport of ions and polar molecules

A
  • channel proteins
  • transporter (carrier) protein
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10
Q

describe the trends of ions and their intra/extra cellular concentrations

A

everything is lower inside the cell than outside, except for K+

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11
Q

what is passive transport

A

when molecules move from an area of high conc to low

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12
Q

what is active transport

A

requires input of energy and can move molecules against their conc gradients

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13
Q

what is another word for passive transport

A

diffusion

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14
Q

passive diffusion is affected by what

A
  • concentration
  • charge
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15
Q

the transport of uncharged molecules is primarily governed by what

A

concentration

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16
Q

the transport of charged molecules is governed by what

A
  • concentration
  • voltage gradients
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17
Q

water can move passively across the membrane down its concentration gradient how

A

osmosis

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18
Q

what is hypertonic

A

water conc in < water conc out

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19
Q

what is isotonic

A

water conc in = water conc out

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20
Q

what is hypotonic

A

water conc in > water conc out

21
Q

is osmosis passive or active transport

A

passive

22
Q

what allows water to move more rapidly across a membrane

A

specialized channel proteins called aquaporins

23
Q

do cells have additional mechanisms to avoid osmotic swelling

A

some do

24
Q

how do protozoans avoid osmotic swelling

A

using contractile vacuoles that periodically discharge their contents to the exterior

25
Q

how do plant cells avoid osmotic swelling

A

touch cell walls can tolerate large osmotic differences (they fight the gradients)

26
Q

how do animal cells avoid osmotic swelling

A

use transmembrane pumps to expel solutes (like Na+ ions that tend to leak into the cell)

27
Q

what proteins help move materials across a membrane

A
  • there are many types
  • each membrane has its own characteristic set of transport proteins
28
Q

when a substance is moving against the electrochemical gradient, what is needed

A

an input of energy

29
Q

what are gradient-driven pumps

A

transporters that facilitate the movement of 2 different molecules

30
Q

what is a symport gradient-driven pump

A

2 diff molecules being moved in the same direction

31
Q

what is an antiport gradient-driven pump

A

2 diff molecules being moved in opposite directions

32
Q

what kind of pump are transporters that move a single type of molecule via conc gradient

A

trick question: they are not considered pumps as no external energy is required

33
Q

can glucode diffuse passively in intestinal epithelial cells

A
  • no
  • glucose conc is higher inside than in lumen or blood
34
Q

describe the Na+/glucose symport

A
  • glucose conc is higher inside intestinal epithelial cells than in lumen or blood
  • so it cannot diffuse passively
  • Na+ is driven into the cell by the electrochemical gradient
  • glucose is actively transported into the cell by the symport (if Na+ is going in, then glucose need to too)
  • Na+ is actively transported out of the cell by the Na+/K+ pump to maintain the gradient needed
35
Q

what uses most of the energy in our bodies

A

Na+/K+ pump

36
Q

describe the steps in the Na+/K+ pump

A
  • Na+ binds
  • pump phosphorylates itself, hydrolyzing ATP
  • phosphorylation triggers conformational change and Na+ is ejected
  • K+ binds
  • pump dephosphorylates itself
  • pump returns to original conformation and K+ is ejected
37
Q

what pump do animal and plant cells use to setup gradients that drive the movement of ions and soluted

A

Na+ pump

38
Q

what are channel proteins

A

aqueous pores that allow passive movement of small, water soluble molecules across a membrane

39
Q

are channel proteins selective

A
  • yes, they are selective for a particular ion
  • based on size, shape, distribution of charged amino acids
40
Q

are channel proteins continuously open

A
  • most are gated, requiring stimulus to switch between open and closed
41
Q

what channels are needed for nerve cells

A
  • voltage-gated channels
  • distribution of ions on either side of the membrane gives rise to the membrane potential
42
Q

describe how K+ leak channels work

A
  • high internal conc of K+ is maintained by Na+/K+ pump
  • K+ also moves across membranes through K+ leak channels
  • it is drawn into the cell to balance neg changed macromolecules (also leaks out down its conc gradient until electrochemical equilibrium is reached)
43
Q

are K+ leak channels uni or bi direction

A

bi directional

44
Q

what is a large contributor to the potential difference across membranes

A

K+

45
Q

describe how an action potential occurs in nerves

A
  • resting potential of -60mv
  • a stimulus increasing the charge to -40mv, and an action potential occurs
  • voltage-gated Na+ channels are opened and ions rush in, increasing the charge to +40
  • Na+ channels then close and are briefly inactivated
  • K+ moves out of the cell, repolarizing the membrane
46
Q

what happens when a nerve signal reached the terminal

A
  • Ca2+ channels open
  • the influx of ions causes vesicles to fuse w the plasma membrane
  • neurotransmitters stores in vesicles are released into the synaptic cleft
  • neurotransmitters bind to channel proteins on adjacent cells
  • these channels open and ions flow into the cell, making a membrane potential
47
Q

describe how channel proteins work for hearing

A
  • ears have stereocilia which vibrates in response to sound
  • these movements cause the mechanically-gated ion channels to open, eliciting a response
48
Q
A

Cell Bio (11 decks)

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