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27 Cards in this Set
- Front
- Back
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What is the charge valence (z) that ions in solution have?
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z = +2 for Ca, z = +1 for K, z = -1 for Cl-
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What is the elementary charge of one electron?
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e0 = 1.6022 x 10^(-19)
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What is the charge of a single ion? (q0)
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measured in coulombs, it is the product of its valence and the elementary charge: q0=ze0
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Why do you need a selective protein channel for movement of ions across a lipid membrane?
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1. Otherwise ions would have to diffuse, which is slow and time-costly
2. The energy to transfer the ion would mean it would have to move across the low energy field that is the plasma membrane, which is something it doesn't want to do |
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What is the equation to calculate the electric field in a cell?
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Ef = Vm/membrane thickness
Vm = electrical potential difference across a membrane |
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What characteristic does Vm exhibit in excitable cells such as neurons, cardiac cells, muscle cells etc?
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Vm exhibits characteristic time-dependent changes in response to electrical or chemical stimulation.
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What role do ATP pump proteins play in establishing ion gradients?
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ATP-dependent ion pumps set up the electrical potential across membranes by using the energy of ATP hydrolysis to set up and maintain unequal concentration gradients across membranes
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What pumps are responsible for maintaining normal gradients of Na, K and Ca?
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Na/K pump and Ca pump
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Why are the reactions catalyzed by the Na/K ATPase and the Ca pump electrogenic?
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Because the reactions catalyzed by these ion transport enzymes leads to separation of charge across the membrane.
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What causes the separation of charges across the membrane?
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The resting potential and electrical driving force
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How do excitable cells have the ability to set up and maintain unequal distributions of soluble ions?
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Electrogenic transporters that set up an electrical potential across the membrane.
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In the horowicz/hodkin experiment what was the purpose of increasing [K]outside cell while simultaneously reducing [Na] outside the cell?
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To maintain constant osmolality
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How do you calculate the Nernst potential for K, Na, Ca or Cl?
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Ex = ((RT)/(ZxF))(log([X]o)/([x]i))
R= universal gas constant (8.314 J/C/mol) Zx = ion charge (i.e. Na = +1; Ca = +2) F = Faraday constant 96,484 C/mo T = Temperature in K = 273 + deg. C x = ion of interest *for chlorine the equation is modified to accommodate Cl's negative charge |
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What are the concentrations of Na, K, Ca and Cl inside and outside the cell at rest?
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ion [ ]outside [ ]inside Vx
K = 4.5 155 -95 Na= 145 12 67 Ca= 1 10^(-4) 123 Cl-= 116 4.2 -89 |
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What do currents carried by ions depend on?
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1. Concentration of ions on both sides of the membrane
2. membrane potential 3. permeability of the membrane to each ion. |
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What does the electrodiffusion model of ion diffusion assume?
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1. Membrane of constant thickness
2. Constant electric field 3. ions separated by a membrane and move independently of one another 4. Diffusion and partition coefficients for each ion. |
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What ion determines Vm of the cell at rest?
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Potassium, b/c the membrane is most permeable to K, so the resting membrane potential lies closest to potassium
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What direction does potassium want to diffuse just above/below of -95 mV?
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below (more negative) -95mV : K current is inward b/c of strong neg. potential inside cell
above (more positive) -95mV : K current is outward b/c of electrochemical gradient outwards |
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What determines total membrane current?
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A combination of P0 and individual conductance and total number of channels
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How do you calculate the current carried by an individual channel?
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I = VG
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Why does the membrane function a lot like a capacitor?
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Because it separates charge and the proteins are the resistors
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What is current through any channel dependent on?
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1. Channel conductance
2. membrane potential 3. ionic equilibrium potential of a particular ion. |
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How can you calculate the current through any channel?
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Ix = Gx (Vm - Ex)
Gx = conductance Vm = membrane potential Ex = Ionic equilibrium potential of a particular ion. |
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What is the patch clamp method?
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1. Using micromanipulators the patch pipette is brought into contact w/ cell surface. Suction is applied to form a tight high resistance seal
2. Breaking the membrane allows whole cell current to be measured from all channels of interest. 3. This allows the probability of opening (P0) can be measured |
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What channel is blocked by tetrodotoxin?
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Sodium channel
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How can information from the use of the patch clamp method be read?
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1. the first recording is the opening of a single Na channel
2. the smallest nearly rectangular transitions of current correspond to the opening and closing of a single Na channel. *this represents a low P0 b/c over most of the depolarization sweep there is no Na current. 3. When two channels in the patch are open simultaneously, the measured current level is an integral multiple of the single-channel or unitary transition. *this represents a medium P0 |
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What is the conclusion that can be drawn from the patch-clamp method?
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*Channel openings are random, single and multiple channels can open and close. There are at least three gating modes, High P0, Medium P0, and low P0.
*The sum total of current at any time represents the number of channels open, the conductance and P0. |
