Term
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Definition
| A property of biological membranes that allows them to regulate the passage of substances. |
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Term
| Amphipathic (am′-fē-path′-ik) |
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Definition
| Having both a hydrophilic region and a hydrophobic region. |
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Term
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Definition
| The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids. |
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Term
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Definition
| Typically a transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane and with hydrophilic regions in contact with the aqueous solution on either side of the membrane (or lining the channel in the case of a channel protein). |
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Term
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Definition
| A protein loosely bound to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer. |
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Definition
| A lipid with covalently attached carbohydrate(s). |
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Term
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Definition
| A protein with one or more carbohydrates covalently attached to it. |
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Term
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Definition
| A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane. |
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Term
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Definition
| A channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of water across the membrane. |
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Term
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Definition
| The spontaneous movement of a substance down its concentration gradient, from a region where it is more concentrated to a region where it is less concentrated. |
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Term
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Definition
| The diffusion of a substance across a biological membrane with no expenditure of energy. |
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Term
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Definition
| A region along which the density of a chemical substance increases or decreases. |
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Term
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Definition
| The diffusion of water across a selectively permeable membrane. |
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Term
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Definition
| The ability of a solution surrounding a cell to cause that cell to gain or lose water. |
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Term
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Definition
| Referring to a solution that, when surrounding a cell, has no effect on the passage of water into or out of the cell. |
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Term
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Definition
| Referring to a solution that, when surrounding a cell, will cause the cell to lose water. |
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Term
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Definition
| Referring to a solution that, when surrounding a cell, will cause the cell to take up water. |
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Term
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Definition
| Regulation of solute concentrations and water balance by a cell or organism. |
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Term
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Definition
| Swollen or distended, as in plant cells. (A walled cell becomes turgid if it has a greater solute concentration than its surroundings, resulting in entry of water.) |
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Term
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Definition
| Limp. Lacking in stiffness or firmness, as in a plant cell in surroundings where there is no tendency for water to enter the cell. |
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Term
| Plasmolysis (plaz-mol′-uh-sis) |
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Definition
| A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment. |
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Term
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Definition
| The spontaneous passage of molecules or ions across a biological membrane with the assistance of specific transmembrane transport proteins. |
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Term
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Definition
| A transmembrane protein channel that allows a specific ion to flow across the membrane down its concentration gradient. |
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Term
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Definition
| A transmembrane protein channel that opens or closes in response to a particular stimulus. |
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Term
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Definition
| The movement of a substance across a cell membrane, with an expenditure of energy, against its concentration or electrochemical gradient; mediated by specific transport proteins. |
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Term
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Definition
| A transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell. |
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Term
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Definition
| The difference in electrical charge (voltage) across a cell’s plasma membrane, due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances. |
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Term
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Definition
| The diffusion gradient of an ion, which is affected by both the concentration difference of the ion across a membrane (a chemical force) and the ion’s tendency to move relative to the membrane potential (an electrical force). |
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Term
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Definition
| An ion transport protein that generates voltage across a membrane. |
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Term
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Definition
| An active transport protein in a cell membrane that uses ATP to transport hydrogen ions out of a cell against their concentration gradient, generating a membrane potential in the process. |
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Term
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Definition
| The coupling of the “downhill” diffusion of one substance to the “uphill” transport of another against its own concentration gradient. |
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Term
| Endocytosis (en′-dō-sī-tō′-sis) |
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Definition
| Cellular uptake of biological molecules and particulate matter via formation of new vesicles from the plasma membrane. |
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Term
| Phagocytosis (fag′-ō-sī-tō′-sis) |
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Definition
| A type of endocytosis in which large particulate substances are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells). |
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Term
| Pinocytosis (pī′-nō-sī-tō′-sis) |
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Definition
| A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes. |
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Term
| receptor-mediated endocytosis (en′-dō-sī-tō′-sis) |
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Definition
| The movement of specific molecules into a cell by the inward budding of membranous vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances. |
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Term
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Definition
| A molecule that binds specifically to another molecule, usually a larger one. |
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Term
| Exocytosis (ek′-sō-sī-tō′-sis) |
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Definition
| The cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane. |
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