Term
| How is a Langmuir trough experiment set up? |
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Definition
| water-filled trough with moveable barrier, known amount of oil added on one side of the barrier |
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Term
| What is the "maximum coverage" part of the Langmuir trough experiment? |
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Definition
| the barrier slides, increasing the area to be covered by oil until layer is just one molecule thick |
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Term
| What is the "overextended" part of the Langmuir trough experiment? |
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Definition
| the oil can no longer cover the entire area |
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Term
| 2 parts of an individual lipid molecule & how they interact with water |
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Definition
1. hydrophilic heads embedded in water
2. hydrophobic tails sticking away |
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Term
| describe the electrical properties of water |
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Definition
| one end has a slight negative charge, one end has a slight positive charge |
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Term
| describe how being a polar molecule helps water dissociate ionic compounds such as salts (NaCl, KCl) in solution |
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Definition
| slight negative charge of oxygen is attracted to positive ions; slight positive charges of hydrogens attract positive ions |
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Term
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Definition
| water that surrounds ions dissolved in an extracellular solution |
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Term
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Definition
| the selectivity filter for each channel |
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Term
| How do carbonyl oxygens (negatively charged) of the TVGYG sequence of amino acids orient themselves in the pore loop? |
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Definition
| oriented so negative oxygens are lining the pore |
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Term
| Do multiple ions pass through the channel at a time or is it a one-by-one process? |
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Definition
| multiple ions pass through the channel at a time |
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Term
| Are ions passing through a channel held in close proximity or far away from each other? |
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Definition
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Term
| How does the "like repels like" theory explain ion movement through channels? |
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Definition
| because each ion has the same charge, electrostatic repulsion drives ions through the channel quickly |
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Term
| How do waters of hydration affect the diameters of sodium & potassium ions? |
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Definition
| waters of hydration make the diameters of sodium & potassium ions much greater than the width of the pore |
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Term
| ______ must be removed for the ion to pass through the pore |
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Definition
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Term
| Is energy required to remove the water shell from ions passing through a channel? |
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Definition
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Term
| Is it harder to remove a water shell from a smaller or larger ion? |
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Definition
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Term
| Within the pore of potassium channels, _____ strip the water molecules off of the ion |
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Definition
| negatively charged amino acids |
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Term
| How are potassium ions stabilized as they pass through channels? |
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Definition
| negative charges of the amino acids in the pore stabilize the dehydrated potassium ion |
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Term
| Why do the waters of hydration need to be stripped from the potassium ion to allow it to pass through the channel? |
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Definition
| makes the potassium ion small enough to get through the channel |
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Term
| Within the pore of sodium channels, ______ strip the water molecules off of the ion |
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Definition
| negatively charged amino acids |
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Term
| How are sodium ions stabilized as they pass through channels? |
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Definition
| the negative charges in the pore stabilize the sodium ion |
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Term
| Does it take more energy to strip water off of sodium or potassium ions? |
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Definition
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Term
| How many water molecules stay attached to the sodium ion as it passes through the channel? |
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Definition
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Term
| Is the pore diameter of sodium channels or potassium channels greater? |
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Definition
| sodium channels (even though sodium is the smaller ion...comes from the waters of hydration that stay attached) |
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Term
| How does the sodium channel stop potassium ions from passing through? |
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Definition
| the geometry of the sodium channel pore is such that potassium ions could not be stabilized so the channel remains selective for sodium |
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Term
| Why are electric ray membranes used to study ACh receptors? |
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Definition
| the membrane has a super dense amount of ACh receptors (good for studying) |
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Term
| The ACh receptor is somewhat between a _____ & _____ in their structure |
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Definition
| ligand-gated & voltage-gated channel |
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Term
| 5 subunits in an ACh receptor |
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Definition
| two alphas, a beta, a delta, & a gamma |
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Term
| Each ACh receptor subunit has _____ transmembrane regions |
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Definition
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Term
| 2 kinds of nicotinic ACh receptors |
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Definition
1. homomeric = all 5 subunits are the same
2. heteromeric = not all five are the same |
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Term
| 2 features every ACh receptor has in common |
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Definition
1. 5 subunits
2. each subunit has 4 transmembrane regions |
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Term
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Definition
| you mutate one of the amino acids |
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Term
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Definition
| you choose exactly where an amino acid is mutated |
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Term
| example of a site-directed mutagenesis |
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Definition
| the SCAM method for identifying the p-loop |
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Term
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Definition
| system of "primed" numbering used to examine the M2 helices of ACh receptors |
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Term
| 3 common structural features for the nAChR "family" of receptors |
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Definition
1. 5 subunits
2. 4 TMR per subunit
3. no P region; pore lined by M2 |
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Term
| 5 differences between ligand-gated ion channels & voltage-gated ion channels |
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Definition
1. gating (voltage vs. ligand binding)
2. selectivity
3. # of domains
4. # of TMR in each domain
5. obviously different functions |
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Term
| What problem used to arise when attempting to record current through a single ion channel? |
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Definition
| on a typical recording setup, noise levels would overpower the current on the read-out |
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Term
| Before modern techniques, how would scientists record current through a single ion channel & interpret the read-out? |
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Definition
| difference of noise between rest & when ACh is present can be attributed to ion flow through the channels |
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Term
| Erwin Neher & Bert Sakmann |
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Definition
| developed the patch-clamp technique! |
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Term
| Where did Neher & Sakmann realize that noise was coming from in current recording read-outs? |
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Definition
| current escaping around the glass microelectrode that is inserted in the cell |
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Term
| Inside diameter of the opening in patch-clamp technique microelectrodes is usually only about _____! |
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Definition
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Term
| How do you bring the membrane up into the pipette in patch-clamp technique? |
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Definition
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Term
| How does the patch-clamp technique greatly reduce noise? |
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Definition
| giga-seal made between the membrane & the glass of the pipette |
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Term
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Definition
| membrane bubbled into the electrode |
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Term
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Definition
| start with cell attached but pull off that part of the membrane! |
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Term
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Definition
| start with cell-attached & apply more suction |
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Term
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Definition
| start with whole-cell & pull away! |
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