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14 Cards in this Set
- Front
- Back
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Action Potential
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-occurs when Na+ channels in cell membrane open and Na+ ions move down their concentration into the cell making the cell membrane potential more positive
--> increase from -70mV to as high as +50mV *causes depolarization (increasing of membrane potential) |
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Affects of the Action Potential
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1) triggers the opening of nearby voltage-gated K+ channels
2) stimulates the opening of additional Na+ channels further along the axon |
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Opening of K+ channels cause
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-K+ ions to move out of the cell down their concentration gradient
-this restores the membrane potential to about -70mv AKA: repolarization |
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myelin sheath
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-structure consisting of several layers of membrane coiled around the axon giving it insulation
-rich in sphingomyelins -allows action potential to propagate axon MUCH faster -"jumps" from node to node |
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Ion channels have
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high selectivity
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The high selectivity of K+ reflects
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-the geometry of the selectivity filter
selectivity filter = arrangement of protein groups that define the extracellular mouth of the pore |
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What makes the K+ ion channel so specific not allowing smaller molecules than K+ (ex: Na+) pass through?
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-at one point, pore narrows to ~3 angstroms, and 4 polypeptide backbones fold so that their carbonyl groups project into the pore
-carbonyl oxygens arranged w/ geometry suitable for coordinating desolvated K+ ion as they move through **Na+ too small to coordinate with the carbonyl groups & therefore, excluded from the pore |
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K+ channels are what kind of channel?
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Voltage-gated ion channel
*opens in response to depolarization |
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Why does an actin potential only move forward??
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Na+ and K+ channels close and can't re-open for a little while
K+ -N-terminal of protein block the cytoplasmic opening of the pore |
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Transport in Cells
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1. non-mediated
-ex: simple diffusion 2. mediated- requires carrier protein A) passive mediated transport -ex: facilitated diffusion B) active transport i) primary ii) secondary |
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3 different types of mediated transport
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1) uniport
2) symport 3) antiport |
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uniport
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*type of mediated transport
moves a single substance across the membrane at a time |
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symport
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*type of mediated transport
transports two different substances across the membrane in the SAME direction |
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antiport
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*type of mediated transport
transports two different substances across the membrane in DIFFERENT directions |
