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Chapter 8
Membrane Structure and Function
26
Biology
Undergraduate 1
09/19/2006

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Term
Amphipathic Molecule
Definition
A molecule that has both a hydrophilic region and a hydrophobic region.
Term
Phospholipids
Definition
Molecules that constitute the inner bilayer of biological membranes, having a polar, hydrophilic head and a nonpolar, hydrophobic tail.
Term
Fluid Mosaic Model
Definition
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.
Term
Diffusion
Definition
The spontaneous tendency of a substance to move down its concentration gradient from a more concentrated to a less concentrated area.
Term
Concentration gradient
Definition
The change in solute concentration per unit distance in solute
Term
Passive Transport
Definition
The diffusion of a substance across a biological membrane
Term
Hypertonic
Definition
the solution with a higher concentration of solutes is said to be hypertonic
Term
Hypotonic
Definition
The solution with a lower concentration of solutes.
Term
Isotonic
Definition
Solutions of equal solute concentration
Term
Osmosis
Definition
Diffusion of water across a selectively permeable membrane is a special case of passive transport called osmosis
Term
Osmoregulation
Definition
the control of water balance
Term
Plasmolysis
Definition
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.
Term
Facilitated Diffusion
Definition
The spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients.
Term
Gated channels
Definition
an electrical of chemical stimulus causes some proteins to open
Term
Active Transport
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.
Term
Sodium-potassium pump
Definition
A special transport protein in the plasma membrane of animal cells that transports sodium out of potassium into the cell against their concentration gradients.
Term
Membrane Potential
Definition
The charge difference between the cytoplasm and extracellular fluid in all cells, due to the differential distributions of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.
Term
Electrochemical gradient
Definition
The diffusion gradient of an ion, representing a type of potential energy that accounts for both the concentration difference for the ion across a membrane and its tendency to move relative to the membrane potential.
Term
Electrogenic pump
Definition
An ion transport protein generating voltage across the membrane.
Term
Proton pump
Definition
An active transport mechanism in cell membranes that consumes ATP to force hydrogen ions out of a cell and, in the process, generates membrane potential.
Term
Cotransport
Definition
The coupling of the “downhill” diffusion of one substance to the “uphill” transport of another against its own concentration gradient.
Term
Exocytosis
Definition
The cellular secretion of macromolecules by the fusion of vesicles with the plasma membrane.
Term
Endocytosis
Definition
The cellular uptake of macromoles and particulate substances by localized regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle.
Term
Phagocytosis
Definition
A type of endocytosis involving large, particulate substances.
Term
Pinocytosis
Definition
A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.
Term
Receptor-mediated endocytosis
Definition
The movement of specific molecules into a cell by the inward budding of membraneous vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to aquire bulk quantities of specific substances.
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