Term
| The membrane is a highly selective filter that... |
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Definition
1. maintains unequal concentrations of ions
2. allows nutrients to enter and waste the cell |
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Term
| What does a membrane consist of? |
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Definition
1. phosholipid bilayer
2. proteins |
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Term
| What are the three different classes of phospholipids? |
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Definition
1. phosphoglycerides
2. sphingolipids
3. sterols |
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Term
| What is a phosphoglyceride? |
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Definition
| Amphipatic (polar head, apolar tail) molecule with a glyceride backbone |
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Term
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Definition
| Amphipatic molecule with a sphingosine backbone |
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Term
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Definition
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Term
| What is our phospholipid bilayer referred to as? |
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Definition
| Singer-Nicolson Fluid Mosaic Model |
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Term
| What is the purpose of having proteins in the membrane? |
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Definition
| To allow the passage of ions since the membrane is impermeable to them |
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Term
| What are some functions of proteins? |
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Definition
1. enzymes
2. receptors for hormones
3. passive channels/pores
4. pumps for active transport
5. carriers for passive transport
6. recognition of molecules |
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Term
| What are the two main functions of the membrane? |
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Definition
1. To control solute concentrations
2. To store energy to do work |
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Term
| How does the membrane set up a membrane potential? |
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Definition
1. By establishing a concentration (electrochemical) gradient using chemical energy
2. By establishing charge separation using electrical energy |
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Term
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Definition
| The passive diffusion of solutes across a barrier |
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Term
| What is Fick's Law of Diffusion? |
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Definition
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Term
| What does Fick's Law tell us? |
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Definition
| That the amount of a substance crossing a unit area per time is equal to the product of the permeability constant and the change in concentration across the membrane |
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Term
| Does every cell carry a membrane potential? |
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Definition
| Yes, but only excitable cells can modify it |
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Term
| What is the permeability constant (Px)? |
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Definition
| Depends on how soluble a solute is in the membrane |
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Term
| How does the permeability constant apply to nonpolar substances? |
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Definition
| Nonpolar substances have a higher permeability constant therefore they are more permeable |
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Term
| What is the equation for permeability? |
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Definition
| Px=(DK)/a where D is the diffusion coefficient, K is the partition coefficient, and a is the membrane thickness (usually ~70A |
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Term
| What does the partition coefficient mean? |
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Definition
| It is the ratio of the concentration of a solute in oil and water (oil:water), thus the higher the K the more soluble it is in oil and the more nonpolar it is |
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Term
| What does the diffusion coefficient say? |
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Definition
| As viscosity and molecular size increase, D decreases |
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Term
| Who was Santiago Ramon Y Cajal? |
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Definition
| Spanish neuroscientist who discovered that the nervous system is made up of neurons, discrete signaling elements ("Neuron Doctrine") |
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Term
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Definition
| Italian neuroscientist who discovered histological staining techniques by impregnating the cell with silver grains |
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Term
| How much charge can a capacitor store? |
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Definition
| C=EA/d where E is the dielectric constant, A is the area of the plates, and d is the distance between the plates |
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Term
| What does a capacitor do? |
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Definition
| Although DC current cannot flow through a capacitor, it can store charge and such charge buildup can push charges to circulate |
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Term
| How does capacitance relate to the plasma membrane? |
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Definition
| The plasma membrane is like a capacitor because it can store charge and channels could be seen as resistors |
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Term
| What kind of channels are there? |
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Definition
1. Open (leakage) channels
2. Gated channels (voltage gated, ligand gated, mechanosensory) |
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Term
| What is meant by active transport? |
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Definition
| Requires ATP (energy) to sustain pumps that will maintain the voltage inside (eg: Na/K ATPase pumps 2K in and 3Na out) |
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Term
| What could block the active transport mechanism of the pumps? |
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Definition
| Cardiac glycosides (eg: those found in some toad poisons) |
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Term
| How is a membrane potential measured? |
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Definition
| As the difference in voltage across the membrane; the potential of the inside relative to the outside (~70mV) |
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Term
| At resting potential what is the state of the K and Na ions? |
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Definition
| There is more K in than out and more Na out than in |
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Term
| What does the Nernst equation say? |
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Definition
| At equilibrium, the chemical force of an ion equals its electrical force |
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Term
| What is the equation for the chemical force? |
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Definition
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Term
| What is the equation for electrical force? |
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Definition
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Term
| What are the equilibrium potentials for a cell only permeable to K or Na, respectively? |
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Definition
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Term
| What is the relationship between resting potential and temperature? |
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Definition
| RP is directly proportional to temperature |
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Term
| What did Baker, Hodgkin, and Shaw discover in 1961? |
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Definition
| When they switch the axoplasm of a squid giant axon with its extracellular fluid, the voltage across the membrane reversed to ~+90mV |
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Term
| How much capacitance is usually found across a membrane per square cm? |
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Definition
| 1 microF (10^-6) per square cm |
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Term
| What is the Goldman equation (Constant-Field equation)? |
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Definition
| It takes into account the permeability of the membrane to more than one (monovalent) ion (an expansion of the Nernst equation |
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