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54 Cards in this Set
- Front
- Back
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bimolecular sheet formed by amphipathic molecules in which the hydrophobic moieties are on the inside of the sheet and the hydrophilic ones are on the aqueous outside |
lipid bilayer
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an artificial lipid vesicle that consists of an aqueous compartment enclosed by a lipid bilayer |
liposome |
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What is a lipid raft complex formed by?
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cholesterol and some phospholipids, notably sphingolipids
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Where are lipid raft complexes found? |
concentrated in specific regions within membranes
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What is true about the part of the membrane containing lipid rafts? (3) |
thicker more stable less fluid |
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What may play a role in concentrating proteins that participate in signal-transduction pathways?
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lipid rafts
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What are lipid rafts also called? |
membrane rafts
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proteins found in membranes that interact extensively with the hydrocarbon chains of the membrane lipids and usually span the membrane |
integral membrane proteins
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protein associated with the surface of a membrane by electrostatic and hydrogen-bond interactions |
peripheral membrane protein
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movement of molecules down a concentration gradient |
simple diffusion
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transport of an ion or a molecule down a concentration gradient, where ΔG for the transported species is negative |
facilitated diffusion
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What is facilitated diffusion also called? |
passive transport
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transport of an ion or a molecule against a concentration gradient, where ΔG for the transported species is positive |
active transport
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What must the process of active transport be coupled to? |
an input of free energy from a source such as ATP, an electrochemical gradient, or light
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What is a Na+-K+ pump? |
membrane-bound enzyme that uses the energy of ATP hydrolysis to pump Na+ out of the cell and K+ into the cell, against their concentration gradients
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What is a Na+-K+ pump also called? |
Na+-K+ ATPase
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family of enzymes that use the energy of hydrolysis to move ions across membranes |
P-type ATPases
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reaction mechanism includes a phosphoryl aspartate intermediate |
P-type ATPases
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protein that acts as an ATP-dependent pump that extrudes a wide range of small molecules from cells that express it |
multidrug-resistance (MDR) protein
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What does MDR stand for? |
multidrug-resistance
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What happens when cells are exposed to a drug? |
MDR protein pumps the drug out of the cell before the drug can exert its effects.
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What four domains comprise the MDR protein? |
two membrane-spanning domains and two ATP-binding domains
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What is MDR protein also called? |
P glycoprotein
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What is the ATP-binding domain characteristic of specific ATP-driven pumps that provide the energy needed for the active transport of ions into and out of cells? |
ATP-binding cassette (ABC) domain
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Do ABC transporters contain a membrane-spanning region? |
yes
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uses the energy of the downhill (exergonic) flow of one ion or molecule to power the uphill (endergonic) flow of another |
secondary transporter
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What is a secondary transporter also called? |
cotransporter
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transport system in which a molecule is carried across a membrane in the direction opposite that of an ion, which in turn is pumped back across the membrane through active transport linked to ATP hydrolysis
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antiporter
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transport system in which a molecule is carried across a membrane against its concentration gradient in the same direction as an ion moving down its concentration gradient
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symporter
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passive-transport system for ions capable of very high transport rates
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ion channel
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What do ion channels often display a high degree of? |
specificity for the transported ion
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region of ion-channel proteins that determines the specificity of a particular channel
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selectivity filter
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Predict the effect on membrane-lipid composition if the temperature of a bacterial culture is raised from 37 to 42 degrees Celsius. |
The increase in temperature will increase the fluidity of the membrane. To prevent the membrane from become too fluid, the bacteria will incorporate longer-chain fatty acids into the membrane phospholipids. This alteration will increase van der Waals interactions among the chains and decrease fluidity.
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What determines the direction of flow through an ion channel? |
Ion channels allow ion flow in either direction. In accordance with the Second law of Thermodynamics, ions will flow down their concentration gradient.
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sheetlike structures that are two molecules thick
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membranes
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What are membranes composed of? |
lipids and proteins, both of which are decorated by carbohydrates
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spontaneously form closed bimolecular sheets in aqueous solutions |
membrane lipids
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mediate the transfer of molecules and information across the membrane
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proteins, unique to each membrane
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True or false: membranes are noncovanlent assemblies.
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true
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Is the inside of the cell negative or positive with respect to the outside? |
negative
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What conditions are required for a small molecule to spontaneously pass through a membrane? |
First, the molecule must be lipophilic and, second, the concentration of the molecule must be greater on one side of the membrane than on the other.
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facilitated diffusion
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passive transport
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uses the energy of one gradient to create another |
secondary transporter
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interacts tightly with the membrane interior |
integral membrane protein
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interacts with the border of a membrane
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peripheral membrane protein
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allows rapid movement of molecules down a gradient across a membrane
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channel
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movement against a concentration gradient
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active transport
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can be voltage-gated or ligand-gated
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ion channel
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inhibited by digitalis
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Na+-K+ ATPase
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Somali hunters use arrows that have been dipped in high concentrations of the cardiac glycoside ouabain to kill game. Indeed, there are reports that animals the size of a hippopotamus can be killed by ouabain-treated arrows. Suggest a biochemical basis for the lethal action of ouabain.
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Ouabain, like digitalis, inhibits the Na+-K+ ATPase. The Na+-K+ ATPase is crucial to maintain the sodium gradient that renders neurons and muscle cels electrically excitable. Inhibition of the enzyme shuts down a host of biochemical processes required for life, such as cardiac and respiratory function.
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If the symporter for Na+-K+ ATPase were inhibited, what effect, if any, would such inhibition have on the ATPase?
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Inhibition of the symporter would eventually lead to the inhibition of the ATPase. Because the sodium gradient would not be dissipated by the symporter, the sodium concentration outside the cell would become so great that the hydrolysis of ATP by the ATPase would not provide sufficient energy to pump against such a large gradient.
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What are two fundamental properties of all ion channels?
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Selectivity and the rapid transport of ions.
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A stretch of 20 amino acids is sufficient to form an alpha helix long enough to span the lipid bilayer of a membrane. How could this piece of information be used to search for membrane proteins in a data bank of primary sequences of proteins?
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Databases could be searched for proteins with stretches of 20 hydrophobic amino acids.
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Lipid bilayers are self-sealing. If a hole is introduced, the hole is filled in immediately. What is the energetic basis of this self-sealing?
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The hydrophobic effect. If there is a hole, the hydrophobic tails of the phospholipids will come together, freeing any associated water.
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