| A | B |
|---|
| selective permeability | allows some substances to cross over more easily than others |
| amphipathic | has both a hydrophilic region and a hydrophobic region |
| fluid mosaic model | envision of the membrane as a mosaic of individually inserted protein molecules drifting laterally in a fluid bilayer of phosopholipids |
| integral proteins | transmembrane proteins with hydrophobic regions that completly span the hydrophobic interior of the membrane |
| peripheral proteins | not embedded in the lipid bilayer; they are appendages loosly bound to the surface of the membreane |
| transport | a protein with a hydrophilic channel across the membrane that is selective for a particular solute; ,ay hydrolyze ATP as an energy source to actively pump substances across the membrane |
| enzymatic activity | a protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution |
| signal transduction | membrane with a binding site with a specific shape that fits the shape of a chemical messanger |
| intercellular joining | membrane proteins of adjacent cells may be hooked together in various kinds of junctions |
| cell-cell recognition | some glycoproteins serve as identification tags that are specifically recognized by other cells |
| glycoprotins | proteins with short chains of sugars |
| attachment to the cytoskeleton and extracellular matrix (ECM) | microfiliments or other elements of the cytoskeleton may be bounded to membrane proteins |
| diffusion | result of thermal motion; the tendancy for molecules to spread out into the available space |
| concentration gradient | a substance moving from where it is more concentrated to where it is less concentrated |
| passive transport | the diffusion of a substance across a biological membrane where a cell does not have to expend energy to make it happen |
| hypertonic | solution with a higher concentration of solutes |
| hypotonic | solution with a lower solute concentration |
| isotonic | solutions of equal solute concentration |
| osmosis | the difussion of water across a selectively permeable membrane; a special case of passive transport |
| osmoregulation | the control of water balance |
| turgid | very firm |
| flaccid | limp |
| plasmolysis | a phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall when the cell loses water to a hypertonic environment |
| facilitated diffusion | the spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradient |
| gated channels | stimulus causes them to open or close |
| active transport | the movement of a substance across a biological membrane against its concentration gradient, with the help of energy input and specific transport proteins |
| sodium-potassium pump | 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 |
| membrane potential | voltage across a membrane |
| electrochemical gradient | 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 tendancy to move relative to the membrane potential |
| electrogenic pump | a transport protein that generates voltage across a membrane |
| proton pump | the main electrogenic pump of plants, bacteria, and fungi |
| cotransport | the coupling of the "downhill" diffusion of one substance and the "uphill" transport of another against its own concentration gradient |
| exocytosis | when the cell secretes macromolecules by the fusion of vesicles witht the plasma membrane |
| endocytosis | when the cell takes in macromolecules and particulate matter by froming new vesicles from the plasma membrane |
| phagocytosis | when a cell engulfs a particle by wrapping pseudopodia around it and packaging it within a membrane-enclosed sac large enough to be classified as a vacuole |
| pinocytosis | when the cell "gulps" droplets of extracellular fluid in tiny vesicles |
| receptor mediated endocytosis | the movement of specific molecules into a cell by the inward budding of membranous vesicles containing proteins woth receptor sites specific to the molecules being taken in |
| ligands | a general term for any molecule that binds spicifically to a receptor site of another molecule |
