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47 Cards in this Set
- Front
- Back
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Describe phospholipids
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-Have a glycerol backbone, which is the hydrophilic head, and two fatty acid tails which are hydrophobic
-Cell bilayer is formed by the hydrophobic fails facing each other |
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Describe how lipid-soluble substances interact with the cell bilayer
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-Cross cell membranes because they can dissolve in the hydrophobic lipid bilayer
-Includes O2, CO2, steroid hormones |
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Describe how water-soluble substances interact with the cell bilayer
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-Cannot dissolve in the lipid of the membrane, but may cross through water-filled channels, or pores, or may be transported by carriers
-Includes Na, Cl, glucose, H2O |
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Describe Integral proteins
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-Are anchored to, and imbedded in, the cell membrane through hydrophobic interactions
-May span the cell membrane -Includes ion channels, transport proteins, receptors and guanosine-5’-triphospate (GTP)-binding proteins (G-proteins) |
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Describe Peripheral Proteins
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-Not imbedded in the cell membrane
-Not covalently bound to membrane components -Loosely attached to membrane by electrostatic interactions |
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Describe tight junctions
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-Zona occludens
-Are the attachments between cells (often epithelial cells) -May be an intercellular pathway for solutes, depending on the size, charge, and characteristics of the tight junction -May be “tight” (impermeable) as in the renal distal cell, or “leaky” (permeable) as in the renal proximal tubule and gallbladder |
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Describe Gap junctions
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-Are the attachments between cells that permit intercellular communication
-For example, permit current flow and electrical coupling between myocardial cells |
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Describe the characteristics of simple diffusion
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-Is the only form of transport that is not carrier mediated
-Occurs down an electrochemical gradient -Does not require metabolic energy and is therefore passive |
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Describe the equation for measuring diffusion
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J=-PA(C1-C2)
where J=Flux P=Permeability A=Area C1, C2=Concentrations |
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Describe the properties of simple diffusion (electrochemical gradient, if it is carrier-mediated, if it required metabolic energy, if there is an Na gradient, and the effect on the Na-K pump)
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Electrochemical gradient: Downhill
Carrier mediated: No Metabolic energy: No Na gradient: No Inhibition of Na-K Pump: - |
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Describe the properties of facilitated diffusion (electrochemical gradient, if it is carrier-mediated, if it required metabolic energy, if there is an Na gradient, and the effect on the Na-K pump)
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Electrochemical gradient: Downhill
Carrier mediated: Yes Metabolic energy: No Na gradient: No Inhibition of Na-K Pump: - |
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Describe the properties of primary active transport diffusion (electrochemical gradient, if it is carrier-mediated, if it required metabolic energy, if there is an Na gradient, and the effect on the Na-K pump)
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Electrochemical gradient: Yphill
Carrier mediated:Yes Metabolic energy: Yes Na gradient: - Inhibition of Na-K Pump: Inhibits (If Na-K pump) |
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Describe the properties of cotransport (electrochemical gradient, if it is carrier-mediated, if it required metabolic energy, if there is an Na gradient, and the effect on the Na-K pump)
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Electrochemical gradient: Uphill (Na is downhill)
Carrier mediated: Yes Metabolic energy: Indirect Na gradient: Yes, same direction Inhibition of Na-K Pump: Inhibits |
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Describe the properties of countertransport (electrochemical gradient, if it is carrier-mediated, if it required metabolic energy, if there is an Na gradient, and the effect on the Na-K pump)
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Electrochemical gradient: Uphill (Na is transported downhill)
Carrier mediated: Yes Metabolic energy: Indirect Na gradient: Yes, opposite direction Inhibition of Na-K Pump: Inhibits |
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Describe permeability
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-Is the P in the equation for diffusion
-Describe the ease with which a solute diffuses through a membrane -Depends on the characteristics of the solute and the membrane |
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Describe the factors that increase permeability
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-Increase Oil/water partition coefficient of the solute increases solubility in the lipid of the membrane
-Decreased radius (size) of the solute increases the speed of diffusion -Decreased membrane thickness dereases the diffusion distance |
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Which solutes have the highest permeability in lipid membranes?
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Small hydrophobic solutes
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Describe how hydrophilic solutes cross the cell membrane
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-They do so through water0filled channels, or pores
-If the solute is an ion, the its flux will depend on both the concentration different and the potential difference across the membrane |
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Describe carrier-mediated transport
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-Includes facilitated diffusion and primary and secondary active transport
-The characteristics of carrier-mediated transport are: 1. Stereospecificity 2. Saturation: Transport rate increases as concentration of the solute increases, until the carriers are saturated 3. Competition: Structurally related solutes compete for transport sites on carrier molecules |
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Describe the characteristics of facilitated diffusion
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-Occurs down an electrochemical gradient (“downhill”), similar to simple diffusion
-Does not require metabolic energy and therefore is passive -Is more rapid than simple diffusion -Is carrier-mediated and therefore exhibits stereospecificity, saturation, and competition |
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Describe the characteristics of primary active transport
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-Occurs against an electrochemical gradient
-Requires direct input of metabolic energy in the form of ATP and therefore is active -Is carrier mediated and therefore exhibits stereospecificity, saturation, and competition |
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Describe the Na-K ATPase
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-Transports Na from intracellular to extracellular fluid and K from extracellular to intracellular fluid
-Maintains low intracellular Na and high intracellularK -Both Na and K are transported against their electrochemical gradients -Energy is provided for the terminal phosphate bond of ATP -Usual stoichiometry is 3Na/2K -Specific inhibitors of Na-K ATPase are the cardiac glycoside drugs oubain and digitalis |
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Describe the Ca-ATPase
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-In the sarcoplasmic reticulum or cell membrane
-Transports Ca against an electrochemical gradient -Sarcoplasmic and endoplasmic reticulum Ca ATPase is called SERCA |
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Describe the H-K ATPase (proton pump)
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-In gastric parietal cells
-Transports H into the lumen of the stomach against its electrochemical gradient -Inhibited by omeprazole |
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Describe the characteristics of secondary active transport
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1. The transport of two or more solutes is coupled
2. One of the solutes (usually Na) is transported downhill and provides energy for the uphill transport of the other solutes 3. Metabolic energy is prodiced indirectly from the Na gradient that is maintained across cell membranes. Inhibition of NaK ATPase will decrease transport of Na out of the cell, decrease the transmembrane Na gradient, and eventually inhibit secondary active transport 4. If the solutes move in the same direction across the membrane, it is called cotransport/symport 5. If the solutes move in opposite directions across the cell membranes it is called countertransport, exchange, or antiport |
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Describe osmolarity
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-The concentration of osmotically active particles in a solution
-A colligative property that can be measured by freezing point depression -Can be calculated by: Osmolarity=g*C g=number of particles in solution C=concentration |
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Define isosmotic
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Two solutions that have the same calculated osmolarity
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Define osmosis
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The flow of water across a semipermeable membrane from a solution with low solute concentration to a solution with high solute concentration
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Describe osmotic pressure
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-Calculated by the van't Hoff law:
π=gCRT π=osmotic pressure g=number of particles in solution C=concentration R=gas constant T=absolute temperature |
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Define isotonic
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Two solutions having the same effective osmotic pressure
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Describe the reflection coefficient
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-A number between zero and one that describes the ease with which a solute permeated a membrane
-If the reflection coefficient is one, the solute is impermeable and therefor is retained in the original solution, creates and osmotic pressure, and causes water flow -If the reflection coefficient is zero, the solute is completely permeable and will not exert any osmotic effect |
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Describe how to calculate effective osmotic pressure
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Osmotic pressure * reflection coefficient
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Describe ion channels
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-Integral proteins that span the membrane and, when open, permit the passage of certain ions
-Ion channels are selective based on size of the channel and distribution of charges that line it -Ion channels may be open or closed -The conductance of the channel depends on the probability that the channel is open. |
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Describe voltage-gated channels
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-Opens and closed by changes in membrane potential
-Activation of the Na channel in nerve is opened by depolarization; when open the nerve membrane is permeabile to Na -The inactivation gate of the Na channel in nerve is closed by repolarization; when closed the nerve membrane is impermeable to Na |
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Describe ligand gated channels
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Open and closed by hormones, second messengers, or neurotransmitters
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Describe the diffusion potential
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-The potential different generated across a membrane because of a concentration different of an ion
-Can be generated only if the membrane is permeable to the ion -Size depends on the size of the concentration gradient -Sign depends on whether the diffusion ion is positively or negatively charged -Created by very few ions and therefore do not result in changes in concentration of the diffusion ions |
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Describe equilibrium potential
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The diffusion potential that exactly balances the tendency for diffusion caused by a concentration different
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Describe electrochemical equilibrium
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The chemical and electrical driving forces that act on an ion are equal and opposite and no more net diffusion of the ion occurs
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Describe the Nernst equation
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-Used to calculate the equilibrium potential at a given concentration different of a permeable ion across a cell membrane
-Tells us what potential would exactly balance the tendency for diffusion down the concentration gradient E=-2.3RT/zF * log(Ci/Co) |
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Describe the resting membrane potential
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-Expressed as the measure potential difference across the cell membrane in millivolts
-Express as the intracellular potential relative to the extracellular potential |
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Define depolarization
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Depolarization makes the membrane potential less negative (the cell interior becomes less negative)
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Define hyperpolarization
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Hyperpolarization makes the membrane potential more negative (teh cell interior becomes more negative)
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Define inward current
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Inward current is the flow of positive charge into the cell. Inward current depolarizes the membrane potential
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Define outward current
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The flow of positive charge out of the cell. Outward current hyperpolarizes the membrane potential
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Define action potential
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A property of excitable cells that consists of a rapid depolarization followed by repolarization of the membrane potential
-Action potential have stereotypical size and shape, are propagating, and are all-or-none |
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Define threshold
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The membrane potential at which the action potential is inevitable. At threshold potential, net inward current becomes larger than net outward current. The resulting depolarization become self-sustaining and gives rise to the upstroke of the action potential.
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Define resting membrane potential
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-Approximately -70mV, cell negative
-The result of the high resting conductance to K, which drives the membrane potential toward the K equilibrium potential -At rest, the Na channels are closes and Na conductance is low |
