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Ap Biology Ch. 7

Membrane Structure and Function

QuestionAnswer
selective permeability A property of biological membranes that allows some substances to cross more easily than others
amphipathic molecule a molecule that has both a hydrophilic region and a hydrophobi region
fluid mosaic model The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of individual protein molecules drifting laterally in a fluid bilayer of phospholipids
integral protein typically a transmembrane protein with hydrophobic regions that completely spans the hydrophobic interior of the membrane
peripheral protein A protein appendage losely bound to the surface of a membrane and not embedded in the lipid bilayer
glycolipid A lipid covalently bonded to a carbohydrate
glycoprotein A protein covalently bonded to a carbohydrate
transport protein A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane
aquaporin A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane (osmosis)
diffusion The spontaneous tendancy of a substanc to move down its concentration gradient from a more concentrated to a less concentrated area
concentration gradient increase or decrease in density of chemical substance in an area.Cells often maintain concentration gradients of ions across their membranes.When gradient exists ions or other chemical substances tend move from more concentrated to less concentrated area
passive transport The diffusion of a substance across a biological membrane.
osmosis The diffusion of water across a selectively permiable membrane
tonicity The ability of a solution to cause a cell within it to gain or loose water
isotonic Having the same solute concentration as another solution
hypotonic In comparing two solutions, referring to the one with a lower solute concentration
hypertonic In comparing two solutions, referring to the one with a greater solute concentration
osmoregulation How organisms regulate solute concentrations and balance the gain and loss of water
turgid Very firm. A walled cell becomes turgid if it has a greater solute concentration than its surroundings, resulting in the entry of water
flaccid Limp. A walled cell is flaccid in surroundings where there is no tendency for water to enter
facilitated diffusion The spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients
ion channel Protein channel in a cell membrane that allows passage of a specific ion down its concentration gradient
gated channel A protein channel in a cell membrane that opens or closes in response to a particular stimulus
active transport The movement of a substance across a biological membrane against its concentration gradient or electrochemical 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 transport sodium out of the cell and potassium into the cell against their concentration gradients
mebrane potential charge difference between a cell's cytoplasm and the extracellular fluid due to the differential distribution of ions. Membrane potential effects the potential of excitable cells and the transmembrane movement of all charged substances
electrochemical gradient diffusion gradient of an ion, representing a type of potential energy that accounts for both the concentration difference of the ion and across a membrane and its tendency to move relative to the membrane potential
electrogenic pump an ion transport protein that generates voltage across a membrane
proton pump An active transport mechanism in cell membranes that uses ATP to force hydrogen ions out of a cell, generating a membrane potential in the process
cotransport The coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient
exocytosis The cellular secetion of macromolecules by the fushion of vesicles with the plasma membrane
endocytosis The cellular uptake of macromolecules and particulate substances by localized regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle
ligand a molecule that binds specifically to a receptor site of another molecule
phagocytosis a type of endocytosis involving large, particulate substances, accomplished mainly by macrophages, neutrophils, and dendritic cells
pinocytosis A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes
receptor-mediated endocytosis movement of specific molecules into a cell by the inward budding of membranous vesicles contain proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances
Created by: gnomealot