Term
| liquid-ordered (Lo) state |
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Definition
| a semisolid state formed by the lipids in a bilayer below normal physiological temperatures; all types of motion of individual lipid molecules are strongly constrained; the bilayer is paracrystalline |
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Term
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Definition
| catalyze translocation of the amino-phospholipids phosphatidylethanolamine & phosphatidylserine from the extracellular to the cytosolic leaflet of the plasma membrane to contribute to the asymmetric distribution of phospholipids (phosphatidylethanolamine & phosphatidylserine are primarily in the cytosolic leaflet & the sphingolipids & phosphatidylcholine are in the outer leaflet) |
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Term
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Definition
| move plasma membrane phospholipids from the cytosolic to the extracellular leaflet & are ATP-dependent (like flippases) |
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Term
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Definition
| proteins that move any membrane phospholipid across the bilayer down its concentration gradient; activity is not dependent on ATP |
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Term
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Definition
| the rate of fluorescence recovery after photobleaching; a measure of the rate of lateral diffusion of the lipids |
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Term
| cholesterol-sphingolipids microdomains |
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Definition
| found in the outer monolayer of the plasma membrane & are slightly thicker & more ordered than neighboring microdomains rich in phospholipids & are more difficult to dissolve with nonionic detergents; behave like liquid-ordered sphingolipid rafts adrift in an ocean of liquid-disordered phospholipids |
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Term
| 2 integral membrane proteins to which lipid rafts are remarkably enriched in order to be anchored to the membrane |
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Definition
1. two covalently attached long-chain saturated fatty acids attached through Cys residues
2. GPI-anchored proteins |
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Term
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Definition
| an integral membrane protein with two globular domains connected by a hairpin-shaped hydrophobic domain which binds the protein to the cytoplasmic leaflet of the plasma membrane |
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Term
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Definition
| formed by the presence of caveolin dimers (formed when caveolin associates with cholesterol-rich regions in the membrane)to force the associated lipid bilayer to curve inward; formed in the surface of the cell |
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Term
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Definition
| a superfamily of proteins; can assemble into a crescent-shaped scaffold that binds to the membrane surface to force or favor membrane curvature |
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Term
| 5 things required for specific fusion of two membranes |
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Definition
1. they recognize each other
2. their surfaces become closely apposed (requires the removal of water molecules normally associated with the polar head groups of lipids)
3. their bilayer structures become locally disrupted (results in the fusion of the outer leaflet of each membrane)
4. their bilayers fuse to form a single continuous bilayer
5. the process is triggered at the appropriate time or in response to a specific signal |
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Term
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Definition
| integral proteins; mediate the events of specific fusion by bringing about specific recognition & a transient local distortion of the bilayer structure that favors membrane fusion |
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Term
| What is the relationship between v-SNAREs & t-SNAREs? |
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Definition
| SNAREs in the cytoplasmic face of the intracellular vesicle are called v-SNAREs; those in the target membrane with which the vesicle fuses are called t-SNAREs |
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Term
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Definition
| surface adhesion proteins that mediate a cell's interaction with the extracellular matrix & with other cells (including some pathogens) |
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Definition
| plasma membrane proteins involved in surface adhesion; undergo hemophilic interactions with identical cadherins in an adjacent cell |
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Term
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Definition
| have extracellular domains that bind specific polysaccharides on the surface of an adjacent cell in the presence of Ca2+ |
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Term
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Definition
| how the solute moves when two aqueous compartments containing unequal concentrations of a soluble compound or ion are separated by a permeable divider; goes from the region of higher concentration, through the membrane, to the region of lower concentration until the two compartments have equal solute concentrations |
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Term
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Definition
| a transmembrane electrical gradient that exists when ions of opposite charges are separated by a permeable membrane |
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Term
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Definition
| membrane proteins that speed the movement of a solute across a membrane by facilitating diffusion |
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Term
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Definition
| bind their substrates (molecules & ions) with high specificity, catalyze transport at rates well below the limits of free diffusion, & are saturable in the same sense as are enzymes (there is some substrate concentration above which further increases will not produce a greater rate of transport) |
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Term
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Definition
| generally allow transmembrane movement of ions at rates that are orders of magnitude greater than those typical of transporters (approaching the limit of unhindered diffusion) |
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Definition
| transporters that simply facilitate diffusion down a concentration gradient |
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Term
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Definition
| can drive substrates across the membrane against a concentration gradient (some use energy provided directly by a chemical reaction & some couple uphill transport of one substrate with downhill transport of another) |
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Term
| chloride-bicarbonate exchanger (anion exchange (AE) protein) |
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Definition
| increases the rate of HCO3- transport across the erythrocyte membrane more than a millionfold |
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Term
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Definition
| an exchange in which there is no net transfer of charge |
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Term
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Definition
| ex) the anion exchanger; simultaneously carries two solutes across a membrane |
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Term
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Definition
| the process when the two substrates move in opposite directions (ex. the anion exchanger) |
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Term
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Definition
| two substrates are moved simultaneously in the same direction |
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Definition
| transporters that carry only one substrate (ex. the erythrocyte glucose transporter) |
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Term
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Definition
| results in the accumulation of a solute above equilibrium point |
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Term
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Definition
| solute accumulation is coupled directly to an exergonic chemical reaction (ex. conversion of ATP to ADP + Pi) |
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Term
| secondary active transport |
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Definition
| occurs when endergonic transport of one solute is coupled to the exergonic flow of a different solute that was originally pumped uphill by primary active transport |
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Term
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Definition
| when the solute is an ion & its movement without an accompanying counterion results in the endergonic separation of positive & negative charges to produce an electrical potential |
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Term
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Definition
| a family of active transporters; cation transporters that are reversibly phosphorylated by ATP as part of the transport cycle |
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Term
| sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA) pump |
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Definition
| exists in animal tissues; works with the plasma membrane Ca2+ ATPase pump as uniporters for Ca2+ ions to maintain the cytosolic level of Ca2+ below 1 um |
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Term
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Definition
| a class of proton-transporting ATPases that are responsible for acidifying intracellular compartments in many organisms |
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Term
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Definition
| active transporters that catalyze the uphill transmembrane passage of protons driven by ATP hydrolysis |
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Term
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Definition
| exist in the apical plasma membrane to take up glucose form the intestine in a process driven by the downhill flow of Na+ |
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Term
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Definition
| a family of integral membrane proteins discovered by Peter Agre; provide channels for rapid movement of water molecules across all plasma membranes |
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Term
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Definition
| first recognized in neurons & now known to be present in the plasma membranes of all cells as well as in the intracellular membranes of eukaryotes; provide a mechanism for moving inorganic ions across membranes |
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Term
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Definition
| binding of an extracellular or intracellular small molecule forces an allosteric transition in the protein which opens or closes the channel |
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Term
| voltage-gated ion channels |
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Definition
| a change in transmembrane electrical potential causes a charged protein domain to move relative to the membrane to open or close the channel |
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Term
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Definition
| a technique developed by Erwin Neher & Bert Sakmann in 1976 in which very small currents are measured through a tiny region of the membrane surface containing only one or a few ion-channel molecules |
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Term
| nicotinic acetylcholine receptor |
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Definition
| a well-studied ion channel; functions in the passage of an electric signal from a motor neuron to a muscle fiber in the neuromuscular junction |
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Term
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Definition
| spherical structures that contain anywhere from a few dozen to a few thousand amphipathic molecules |
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Term
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Definition
| a type of lipid aggregate in water; two lipid monolayers form a two-dimensional sheet |
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Term
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Definition
| a hollow sphere formed when the bilayer sheet spontaneously folds back on itself due to the hydrophobic regions at its edges being in contact with water rendering the bilayer sheet relatively unstable |
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Term
| peripheral membrane proteins |
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Definition
| associate with the membrane through electrostatic interactions & hydrogen bonding with the hydrophilic domains of integral proteins & with the polar head groups of membrane lipids |
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Term
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Definition
| found both in the cytosol & in association with membranes |
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Term
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Definition
| describes amino acid location relative to the bilayer; the positively charged Lys, His, & Arg residues of membrane proteins occur more commonly on the cytoplasmic face of membranes |
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Term
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Definition
| a structural motif common in bacterial membrane proteins; 20 or more transmembrane segments for beta sheets that line a cylinder |
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Term
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Definition
| proteins that allow certain polar solutes to cross the outer membrane of gram-negative bacteria (ex. E. coli) that have many-stranded beta barrels lining the polar transmembrane passage |
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