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Chapter 8
Membrane Structure and Function
32
Biology
Not Applicable
05/06/2005

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Term
selective permeability
Definition
allows some substances to cross more easily than others
Term
amphipathic molecule
Definition
a phospholipid that has both a hydrophilic region and a hydrophobic region
Term
fluid mosaic model
Definition
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
Integral proteins
Definition
transmembrane proteins, with hydrophobic regions that completely span the hydrophobic interior of the membrane
Term
peripheral proteins
Definition
appendages loosely bound to the surface of the membrane
Term
transport proteins
Definition
spans the membrane; helps move specific molecules across the membrane
Term
diffusion
Definition
tendency for molecules of any substance to spread out into the available space
Term
passive transport
Definition
diffusion of substance across a biological membrane
Term
concentration gradient
Definition
The relation of two given areas, where the concentration of a particular substance differs between those areas. Diffusion will result in this substance moving along a concentration gradient until the concentration of the two areas becomes equal.
Term
hypertonic
Definition
solution with a higher concentration of solutes
Term
hypotonic
Definition
solution with lower solute concentration
Term
isotonic
Definition
solutions of equal solute concentration
Term
osmosis
Definition
passive transport; diffusion of water across a selectively permeable membrane
Term
osmoregulation
Definition
control of water balance
Term
turgid
Definition
very firm
Term
flaccid
Definition
limp
Term
faccilitated diffusion
Definition
spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradient
Term
plasmolysis
Definition
plasma membrane pulling away from the wall as the plant cell shrivels
Term
gated channels
Definition
a stimulus that cause transport proteins to open or close
Term
active transport
Definition
pumping a molecule across a membrane against its gradient; using it's own metabolic energy
Term
sodium-potassium pump
Definition
exchanges sodium for potassium across the plasma membrane of animal cells
Term
membrane potential
Definition
voltage across a membrane
Term
electrochemical gradient
Definition
combination of forces acting on an ion
Term
electrogenic pump
Definition
transport protein that generates voltage across a membrane
Term
proton pump
Definition
main electrogenic pump of plants, bacteria and fungi; actively transports hydrogen ions (protons) out of the cell
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
secretes macromolecules by the fusion of vesicles with the plasma membrane
Term
endocytosis
Definition
cell takes in macromolecules and particulate matter by forming new vesicles from the plasma membrane
Term
phagocytosis
Definition
a cell engulfs a particle by wrapping pseudopodia around it and packaging it within a membrane enclosed sac
Term
pinocytosis
Definition
cell gulps droplets of extracellular fluid in tiny vesicles
Term
receptor-mediated endocytosis
Definition
movement of specific molecules into a cell by the inward budding of membranous besicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances
Term
ligands
Definition
extracellular substances that bind to the receptors
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