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Definition
| The movement of a substance across a biological membrane against its concentration or electrochemical gradient, with the help of energy input and specific transport proteins. |
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| A molecule that has both a hydrophilic region and a hydrophobic region. |
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| A regular increase of decrease in the intensity or density of a chemical substance. Cells often maintain concentration gradients of H+ions across their membranes. When a gradient exists, the ions or other chemical substances involved tend to move from where they are more concentrated to where they are less concentrated. |
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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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| The diffusion gradient of an ion, representing a type of potential energy that accounts for both the concentration difference of the ion across a membrane and its tendency to move relative to the membrane potential. |
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| An ion transport protein generating voltage across the membrane. |
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| The spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients. |
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| The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of individually inserted protein molecules drifting laterally in a fluid bilayer of phospholipids. |
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| A solution with a greater solute concentration than another, a hypotonic solution. |
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| A solution with a lesser solute concentration than another, a hypertonic solution. |
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| Solutions of equal solute concentration. |
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| A molecule that binds specifically to a receptor site of another molecule. |
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| The charge difference between the cytoplasm and extracellular fluid in all cells, 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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| The diffusion of water across a selectively permeable membrane. |
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Definition
| The diffusion of a substance across a biological membrane. |
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Definition
| A type of endocytosis involving large, particulate substances. |
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Definition
| Molecules that constitute the inner bilayer of biological membranes, having a polar, hydrophilic head and a nonpolar, hydrophobic tail. |
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| A property of biological membranes that allows some substances to cross more easily than others. |
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| A special transport protein in the plasma membrane of animal cells that transports sodium out of and potassium into the cell against their concentration gradients. |
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Definition
| Proteins that span the membrane, allowing hydrophilic substances to avoid contact with the lipid bilayer. |
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