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Cell Bio > L11. Transport across cell membrane > Flashcards

L11. Transport across cell membrane Flashcards

1
Q

what do membrane transport proteins facilitate

A

the movement of water soluble molecules

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2
Q

what does the rate of diffusion depend on

A

molecular size and solubility

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3
Q

rate of diffusion - molecules ranked from highest to lowest diffusion

A
  1. small nonpolar molecules (all pass through)
  2. small uncharged, polar molecules
  3. larger uncharged polar molecules
  4. ions (none pass through)
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4
Q

ion concentrations - Na+

A
  • sodium
  • low inside cell
  • high outside cell
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5
Q

ion concentrations - K+

A
  • potassium
  • low inside cell
  • high outside cell
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6
Q

ion concentrations - Ca2+

A
  • calcium
  • really low inside cell
  • high outside cell
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7
Q

explain the two components of an electrochemical gradient

A
  • electro: membrane potential
  • chemical: concentration gradient
  • they can either work together or oppose each other
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8
Q

two components of an electrochemical gradient - what happens as concentration gradient and membrane potential work together

A

increases solute movement

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9
Q

two components of an electrochemical gradient - what happens as concentration gradient and membrane potential oppose each other

A

the electrochemical driving force is decreased

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10
Q

what solutes can transporters and channels move across the membrane

A

inorganic ions and small, polar organic molecules

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11
Q

explain how transporters can move molecules

A
  • taking a molecule from one side and physically move it to another side via conformational changes
  • can be used with active or passive transport
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12
Q

explain how channels can move molecules

A
  • they do not stay open
  • only uses passive transport
  • faster then transporters
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13
Q

explain active transport

A
  • molecules are moved against the concentration gradient (less -> more)
  • requires energy (not only ATP)
  • only transporters can do this
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14
Q

explain the types of transporters

A
  1. uniport
  2. symport
  3. antiport
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14
Q

explain passive transport

A
  • molecules move down their concentration gradient (more -> less)
  • occurs spontaneously (no energy needed)
  • can be transporter- or channel-mediated
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15
Q

types of transporters - uniport

A
  • only moves one molecule
  • can be against or toward the gradient
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16
Q

types of transporters - symport

A
  • type of coupled transport
  • both molecules go in the same direction
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17
Q

types of transporters - antiport

A
  • type of coupled transport
  • molecules to in opposite directions
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18
Q

types of transporters - what is coupled transport

A

using the movement of one molecule going toward the gradient to pay for the movement of another molecule moving against the gradient

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19
Q

what are the three mechanisms of active transport

A
  • coupled pump
  • ATP-driven pump
  • light driven pump
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20
Q

passive transport - explain the conformational change in transporters

A
  1. outward-open
  2. occluded
  3. inward-open
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21
Q

passive transport with transporters - outward-open

A

binding sites are exposed on the outside of the cell

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22
Q

passive transport with transporters - occuluded

A

both sides are closed and binding site is not accessible

23
Q

passive transporter with transporters - inward-open

A

binding sites are exposed on the inside of the cell

24
Q

explain the Na+/K+ pump

A
  • it uses ATP hydrolysis to pump Na+ out of cells and K+ into cells
  • concentration gradient of Na+ along with the membrane potential creates an electrochemical gradient
25
Q

explain the Ca2+ pump

A
  • pumps and Ca2+ from the cytosol into the lumen of the sarcoplasmic reticulum
  • uses ATP hydrolysis
26
Q

what is the glucose/Na+ symporter

A
  • uses the Na+ gradient as an energy source made by the Na+/K+ pump
  • imports glucose against the gradient into the cytosol
  • it uses active transport and it is a symport
27
Q

what are the two glucose transporters that enable gut epithelial cells to transfer glucose

A
  1. Na+ -driven glucose symport
  2. passive glucose uniport
28
Q

two glucose transporters - Na+ -driven glucose symport

A
  • uses Na+ gradient as an energy source
  • takes up glucose actively, creating high concentrations of glucose in cytosol
  • it faces the gut lumen (apical domain)
29
Q

two glucose transporters - passive glucose uniport

A
  • release of glucose down its concentration gradient for use by other tissues
  • faces the extracellular fluid (basal and lateral domains)
30
Q

how do transmembrane pumps work - animal cells

A

the Na+/K+ pump (ATPase) establishes a Na+ gradient that facilitates transport by symports

31
Q

how do transmembrane pumps work - plant cells

A

use H+ gradient created by the H+ pump that facilitates transport by symports

32
Q

how are ion channels selective

A
  • ions are surrounded by a shell of water that will be shed during passage through the channel
  • passage is also narrow so only ions of appropriate charge and size can go through
33
Q

how are ion channels gated

A
  • they are not continuously open
  • they are gated by specific stimuli
34
Q

how are ion channels gated

A
  • voltage-gated
  • ligand-gated (extracellular or intracellular ligand)
  • mechanically-gated
35
Q

membrane potential - when is it zero

A

when there is an exact balance of charges on each side of the membrane

36
Q

membrane potential - when is it non-zero

A

when K+ leak channels cause K+ to leave the cell, creating an imbalance in the membrane

37
Q

how does the [K+] gradient and K+ leak channels aid in generating membrane potential

A
  • K+ is transported into the cell via Na+/K+ pump
  • but as soon as K+ leak channels open, K+ leaves the cell and negative ions don’t cross
  • this causes a charge imbalance that gives rise to membrane potential
38
Q

how does the [K+] gradient and K+ leak channels create the resting membrane potential

A
  • the imbalance from the [K+] gradient and the K+ leak channels stops K+ from leaving the cell
  • the membrane potential will keep K+ inside the cell balanced to the K+ moving down its gradient
  • this causes positive and negative ions to be balanced creating the resting membrane potential
39
Q

typical neuron - what are dendrites

A

provide enlarged surface area to receive signals from other neurons

40
Q

typical neuron - what are axons

A

conduct electrical signals from cell body

41
Q

typical neuron - what are nerve termini

A

serve as passage of the message to other target cells

42
Q

explain the action potential

A
  • it is mediated by voltage gated Na+ channels
  • stimulation causes depolarization
  • if the stimulation is large enough, the Na+ channels open
  • Na+ influx depolarizes the membrane even further
  • this then causes more Na+ channels to open and creates the action potential
43
Q

action potential - what happens to it with distance

A

gets weaker

44
Q

action potential - what is depolarization

A

the membrane potential becoming less negative and instead becomes more positive

45
Q

explain the Na+ channels as the message is propogating

A
  • the electrochemical driving force for Na+ is 0 bc the membrane potential and [Na+] gradient is equal and opposite
  • the channels become will become inactive on a “timer”
46
Q

Na+ channels during message propagation - inactive conformation

A
  • the channel will be closed even when the membrane is depolarized
  • the channel remains inactive until the membrane potential is resorted to a negative value
47
Q

how do K+ channels aid in the action potential

A
  • K+ channels also open in response to depolarization (slower than Na+)
  • they will stay open for as long as the membrane is depolarized
  • K+ leaving helps bring membrane back to resting
  • quicker than K+ leak channels
  • Na+/K+ pumps will then restore the ion gradient
48
Q

how are electrical signals converted to chemical ones

A
  • neurotransmitters convert electrical signal to a chemical one
  • they are stored in synaptic vesicles
49
Q

electrical -> chemical signal - what happens as the action potential reaches a nerve terminal

A
  • it is relayed at a synapse
  • the synaptic vesicle that stores the neurotransmitters then fuse with the plasma membrane
  • this forces the neurotransmitters to go into the synaptic cleft
50
Q

electrical -> chemical signal - voltage gated Ca2+ channels

A
  • when the action potential reaches a nerve terminal, it also opens Ca2+ channels
  • influx of Ca2+ triggers the fusion of vesicle and plasma membranes
51
Q

electrical -> chemical signal - what happens on the synaptic cleft of the postsynaptic target cell

A
  • neurotransmitters bind to their receptors
  • this causes a change in membrane potential in that cell
  • if the signal is large enough, it will propagate an action potential
52
Q

electrical -> chemical signal - what happens when a action potential is triggered in the target cell

A
  • the neurotransmitter is quickly removed from the synaptic cleft via an enzyme or re-uptake
  • this limits the signal duration
53
Q

acetylcholine and the neuromuscular junction - overall structure

A
  • 5 transmembrane protein subunits
  • form a transmitter-gated aqueous pore
  • the pore is lined by 5 transmembrane alpha helices
  • has 2 acetylcholine binding sites
54
Q

acetylcholine and the neuromuscular junction - closed conformation

A

pore is blocked by hydrophobic amino acid side chains in the gate region

55
Q

acetylcholine and the neuromuscular junction - open conformation

A
  • acetylcholine (released by a motor neuron) binds to both binding sites
  • this triggers a conformational change and the hydrophobic side chains moves apart, opening the gate
  • membrane is then depolarized

Cell Bio (21 decks)

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