L11. Transport across cell membrane Flashcards
1
Q
what do membrane transport proteins facilitate
A
the movement of water soluble molecules
2
Q
what does the rate of diffusion depend on
A
molecular size and solubility
3
Q
rate of diffusion - molecules ranked from highest to lowest diffusion
A
- small nonpolar molecules (all pass through)
- small uncharged, polar molecules
- larger uncharged polar molecules
- ions (none pass through)
4
Q
ion concentrations - Na+
A
- sodium
- low inside cell
- high outside cell
5
Q
ion concentrations - K+
A
- potassium
- low inside cell
- high outside cell
6
Q
ion concentrations - Ca2+
A
- calcium
- really low inside cell
- high outside cell
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
8
Q
two components of an electrochemical gradient - what happens as concentration gradient and membrane potential work together
A
increases solute movement
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
10
Q
what solutes can transporters and channels move across the membrane
A
inorganic ions and small, polar organic molecules
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
12
Q
explain how channels can move molecules
A
- they do not stay open
- only uses passive transport
- faster then transporters
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
14
Q
explain the types of transporters
A
- uniport
- symport
- antiport
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
15
Q
types of transporters - uniport
A
- only moves one molecule
- can be against or toward the gradient
16
Q
types of transporters - symport
A
- type of coupled transport
- both molecules go in the same direction
17
Q
types of transporters - antiport
A
- type of coupled transport
- molecules to in opposite directions
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
19
Q
what are the three mechanisms of active transport
A
- coupled pump
- ATP-driven pump
- light driven pump
20
Q
passive transport - explain the conformational change in transporters
A
- outward-open
- occluded
- inward-open
21
Q
passive transport with transporters - outward-open
A
binding sites are exposed on the outside of the cell
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
explain the Na+/K+ pump
- 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
explain the Ca2+ pump
- pumps and Ca2+ from the cytosol into the lumen of the sarcoplasmic reticulum
- uses ATP hydrolysis
26
what is the glucose/Na+ symporter
- 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
what are the two glucose transporters that enable gut epithelial cells to transfer glucose
1. Na+ -driven glucose symport
2. passive glucose uniport
28
two glucose transporters - Na+ -driven glucose symport
- 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
two glucose transporters - passive glucose uniport
- release of glucose down its concentration gradient for use by other tissues
- faces the extracellular fluid (basal and lateral domains)
30
how do transmembrane pumps work - animal cells
the Na+/K+ pump (ATPase) establishes a Na+ gradient that facilitates transport by symports
31
how do transmembrane pumps work - plant cells
use H+ gradient created by the H+ pump that facilitates transport by symports
32
how are ion channels selective
- 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
how are ion channels gated
- they are not continuously open
- they are gated by specific stimuli
34
how are ion channels gated
- voltage-gated
- ligand-gated (extracellular or intracellular ligand)
- mechanically-gated
35
membrane potential - when is it zero
when there is an exact balance of charges on each side of the membrane
36
membrane potential - when is it non-zero
when K+ leak channels cause K+ to leave the cell, creating an imbalance in the membrane
37
how does the [K+] gradient and K+ leak channels aid in generating membrane potential
- 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
how does the [K+] gradient and K+ leak channels create the resting membrane potential
- 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
typical neuron - what are dendrites
provide enlarged surface area to receive signals from other neurons
40
typical neuron - what are axons
conduct electrical signals from cell body
41
typical neuron - what are nerve termini
serve as passage of the message to other target cells
42
explain the action potential
- 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
action potential - what happens to it with distance
gets weaker
44
action potential - what is depolarization
the membrane potential becoming less negative and instead becomes more positive
45
explain the Na+ channels as the message is propogating
- 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
Na+ channels during message propagation - inactive conformation
- 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
how do K+ channels aid in the action potential
- 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
how are electrical signals converted to chemical ones
- neurotransmitters convert electrical signal to a chemical one
- they are stored in synaptic vesicles
49
electrical -> chemical signal - what happens as the action potential reaches a nerve terminal
- 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
electrical -> chemical signal - voltage gated Ca2+ channels
- 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
electrical -> chemical signal - what happens on the synaptic cleft of the postsynaptic target cell
- 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
electrical -> chemical signal - what happens when a action potential is triggered in the target cell
- the neurotransmitter is quickly removed from the synaptic cleft via an enzyme or re-uptake
- this limits the signal duration
53
acetylcholine and the neuromuscular junction - overall structure
- 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
acetylcholine and the neuromuscular junction - closed conformation
pore is blocked by hydrophobic amino acid side chains in the gate region
55
acetylcholine and the neuromuscular junction - open conformation
- 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
