Chapter 7: Membrane Structure And Function Flashcards
Fluid Mosaic Model
The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids
Components of the Phospholipid Bilayer
Phospholipids Integral proteins Transmembrane proteins Peripheral proteins Glycolipid Cholesterol
Integral Proteins
A transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane with hydrophilic regions in contact with the aqueous solution on one or both sides of the membrane
Transmembrane proteins
A type of integral protein that spans the entire membrane
Peripheral protein
A protein loosely bound to the surface of a membrane or to a part of an integral protein and not embedded in the lipid bilayer
Glycolipid
A lipid with one or more covalently attached carbohydrates
A protein with one or more covalently attached carbohydrates
Cholesterol
Functions as a fluidity buffer for animal cells
- the double bonds in cholesterol aid the bilayer in resisting changes in temperature and as a result the fluidity.
Selective permeability
A property of biological membranes that allows them to regulate the passage of substances across them
Depends on both the discriminating barrier of the lipid bilayer and the specific transport proteins built into the membrane
Permeability of the bilayer
Non polar molecules - Since they are hydrophobic they can cross the lipid bilayer easily, without the aid of membrane proteins.
Polar molecules - since they are hydrophilic, they cross very slowly. Charged atoms or molecules are even less likely to penetrate the hydrophobic interior
Proteins that are built into the membrane regulate the transport of polar and charged molecules.
Transport proteins
A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane
Channel proteins
Hydrophilic Channel that certain molecules or ions use as a tunnel through the membrane
Aquaporin
A Channel protein that specifically facilitates osmosis, the diffusion of free water across the membrane
Carrier proteins
Hold onto their passengers and change shape in a way that shuttles them across the membrane
Diffusion
The random thermal motion of particles of liquids, gases or solids. In the presence of a concentrated or electrochemical gradient, diffusion results in the net movement of a substance from a region where it is more concentrated to a region where it is less concentrated
Concentration gradient
A region along which the density of a chemical substance increases or decreases
Passive transport
The diffusion of a substance across a biological membrane with no expenditure of energy
Osmosis
The diffusion of free water across a selectively permeable membrane
Tonicity
The ability of a solution surrounding that cell to gain or lose water
Isotonic
Referring to a solution that, when surrounding a cell, causes no net movement of water into 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 uptake water
Osmoregulation
Regulation of solute concentrations and water balance by a cell or organism
Turgid
Swollen or distended, as in plant cells in surrounding where there is a tendency for water to enter the cell
Flaccid
Limp. As in a plant cell in surrounding where there is a tendency for water to leave the cell
Plasmolysis
A phenomenon in walled cells in which 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
The passage of molecules or ions down their electrochemical gradient across a biological membrane with the assistance of specific transmembrane transport proteins, requiring no energy expenditure
Ion Channel
A transmembrane protein channel that allows a specific ion to diffuse across the membrane down is concentration gradient or electrochemical gradient
Gated Channel
A transmembrane protein channel that opens or closes in response to a particular stimulus
Active Transport
The movement of a substance across a cell membrane against its concentration of electrochemical gradient, mediated by specific transport proteins and requiring an expenditure of energy
Membrane potential
The difference in electrical charges across a cell’s plasma membrane due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances
Electrochemical gradient
The diffusion gradient of an ion, which is affected by both the concentration difference of an ion across a membrane and the ion’s tendency to move relative to the membrane potential
Electrogenic Pump
An active transport protein that generates voltage across a membrane while pumping ions
Sodium Potassium Pump
An active transport protein in the plasma membrane of animal cells that actively transport sodium out of the cell and potassium into the cell.
Proton Pump
An active transport protein in a cell membrane that uses ATP to transport hydrogen ions out of a cell against their concentration gradient, generating a membrane potential in the process
Cotransport
The coupling of one downhill diffusion of one substance to the uphill transport of another against its own concentration gradient.
Exocytosis
the cellular segregation of biological molecules by the fusion of vesicles, containing them within the plasma membrane.
Endocytosis
Cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane
Phagocytosis
Cell engulfs a particle by packing it within a membranous sac and the particle will be digested after the food vacuole fuses with a lysosome
Pinocytosis
Gulps droplets of extracellular fluid into tiny vesicles
Non specific for the substances it transports
Receptor mediated endocytosis
A type of pinocytosis that allows for the transport of specific substances through binding to receptors
