Chapter 7 - Membrane Structure Flashcards
Having both a hydrophilic and hydrophobic region
Amphipathic
The plasma allows some substances to cross it more easily than others
Selective permeability
Currently accepted model of the cell membrane structure, which envisions the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids
Fluid mosaic model
Proteins that penetrate the hydrophobic interior of the lipid bilayer; majority are transmembrane proteins
Integral proteins
Proteins not embedded in the lipid bilayer at all; they are appendages loosely bound to the surface of the membrane often to expose parts of integral proteins
Peripheral proteins
Short, branched chains of carbohydrates covalently bonded to lipids
Glycolipids
Short, branched chains of carbohydrates covalently bound to proteins
Glycoproteins
A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane
Transport proteins
Channel protein that facilitates the passage of water molecules through the membrane in certain cells; allows up to 3 billion water molecules per second
Aqua poring
Movement of particles of any substance so that they spread out into the available space
Diffusion
Region along which the density of a chemical substance increases or decreases
Concentration gradient
Diffusion of free water across a selectively permeable membrane whether artificial or cellular
Osmosis
The ability of a surrounding solution to cause a cell to gain or lose water
Tonicity
No net movement of water across the cell membrane; equal solutes
Isotonic
Solution causing a cell to lose water due to higher concentration of solutes outside the cell
Hypertonic
Solutions causing cell to take up water due to lower concentration of solutes outside the cell
Hypotonic
Control of solute concentrations and water balance
Osmoregulation
very firm; healthy state for most plants (hypotonic)
Turgid
Limp; no net tendency for water to enter the plant cell (isotonic)
Flaccid
Process causing a plant to wilt and can lead to death; caused by hypertonic conditions
Plasmolysis
Polar molecules and ions impeded by the lipid bilayer of the membrane diffuse passively with the help of transport proteins that span the membrane
Facilitated diffusion
Channel proteins that transport ions
Ion channels
Ion channels that open or close in response to stimulus
Gated channels
Movement of a solute across a membrane against its gradient requiring the expenditure of energy
Active transport
Transport system which exchanges Na+ for K+ across the plasma membrane of animal cells
Sodium-potassium pump
Voltage across a membrane ranging from about -50 to -200 millivolts
Membrane potential
Combination of forces acting on an ion; these forces are a chemical force (the ion’s concentration gradient) and an electrical force (the effect of the membrane potential on the ion’s movement)
Electrochemical gradient
Transport protein that generates voltage across a membrane
Electrogenic pump
Main electrogenic pump of plants, fungi, and bacteria which actively transports protons (H+) out of the cell transferring positive charge from the cytoplasm to the extra cellular solution
Proton pump
Mechanism when a transport protein can couple the “downhill” diffusion of the solute to the “uphill” transport of a second substance against its own concentration gradient
Cotransport
Cell secretion of certain molecules by the fusion of vesicles with the plasma membrane
Exocytosis
Cell intake of molecules and particulate matter by forming new vesicles from the plasma membrane
Endocytosis
Any molecule that binds specifically to a receptor site on another molecule
Ligands
Cell engulfs a particle by extending pseudopodia around it and packaging it within a food vacuole; the particle is digested after the vacuole fuses with a lysosome
Phagocytosis
Cell gulps droplets of extra cellular fluid into tiny vesicles
Pinocytosis
Specialized type of pinocytosis that enables the cell to acquire bulk quantities of specific substances even though those may not be concentrated in the extra cellular fluid
Receptor-mediated endocytosis
