Chapter 7: Membrane Structure and Function Flashcards
Selective Permeability
A property of biological membranes that allows them to regulate the passage of substances across them
Amphipathic
Having both a hydrophilic region and a hydrophobic region
Fluid Mosaic Model
- Currently accepted model of cell membrane structure
- Envisions the membrane as a mosaic of protein molecules drifting laterally on a fluid bilateral of phospholipids
Integral Protein
- Transmembrane protein
- Hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane
- Hydrophilic regions in contact with the aqueous solution on one or both sides of the membrane (or lining the channel in the case of a channel protein)
Peripheral Protein
- A protein loosely bound to the surface of a membrane or to part of an integral protein
- Not embedded in the lipid bilayer
Glycolipid
A lipid with one or more covalently attached carbohydrates
Glycoprotein
A protein with one or more covalently attached carbohydrates
Transport Protein
A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane
Aquaporin
A channel protein in a cellular membrane that specifically facilitates osmosis
Diffusion
- Random thermal motion of particles of liquids, gases, or solids in the presence of a concentration of an electrochemical gradient
- Results in the net movement of a substance from a region where it is more concentrated to where it is less concentrated
Concentration Gradient
A region along which the density of a chemical substance increases or decreases
Passive Transport
- Diffusion of a substance across a biological membrane
- No energy used
Osmosis
The diffusion of free water across a selectively permeable membrane
Tonicity
Ability of a solution surrounding a cell to cause that cell to gain or lose water
Isotonic
Referring to a solution that, when surrounding a cell, causes no net movement of water in or out of the cell
Hypertonic
Referring to a solution that, when surrounding a cell, will cause the cell to lose water
Hypotonic
Referring to a solution that, when surrounding a cell, will cause the cell to take up water
Osmoregulation
Regulation of solute concentrations and water balance by a cell or organism
Turgid
- Swollen or distended, as in plant cells
- A walled cell becomes this if it has a lower water potential than its surroundings, resulting in entry of water
Flaccid
- limp or lacking turgor (stiffness or firmness)
- When a plant cell is in surroundings where there is a tendency for water to leave the cell
Plasmolysis
- Phenomenon in walled cells where the cytoplasm shrivels and the plasma membrane pulls away from the cell wall
- Occurs when the cell loses water to a hypertonic environment
Facilitated Diffusion
- Passage of molecules or ions down their electrochemical gradient across a biological membrane
- Specific transmembrane and transport proteins help
- Doesn’t require energy
Ion Channel
Transmembrane protein channel that allows specific ion to diffuse across the membrane down its concentration or electrochemical gradient
Gated Channel
Transmembrane protein channel that opens or closes in response to a particular stimulus
Active Transport
- Movement of a substance across a cell membrane against its concentration or electrochemical gradient
- Mediated by specific transport proteins
- Requires energy
Sodium-Potassium Pump
- Transport protein in the plasma membrane of animal cells
- Actively transports sodium (Na) out of the cell and potassium (K) into the cell
Membrane Potential
- Difference in electrical charge (voltage) across a cell’s plasma membrane due to the differential distribution of ions
- Affects the activity of excitable cells and the transmembrane movement of all charged substances
Electrogenic Pump
Active transport protein that generates voltage across a membrane while pumping ions
Electrochemical Gradient
- Diffusion gradient of an ion
- Affected by both the concentration difference of an ion across a membrane and the ion’s tendency to move relative to the the membrane potential (an electrical force)
Proton Pump
- Active transport protein in a cell membrane
- Uses ATP to transport hydrogen ions out of a cell against their concentration gradient
- Generates a membrane potential
Cotransport
Coupling of the “downhill” diffusion of one substance to the “uphill” transport of another against its own concentration gradient
Exocytosis
Cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane
Endocytosis
Cellular uptake of biological molecules and particulate matter via formation of new vesicles from the plasma membrane
