Cell Membranes Flashcards
Cellular membranes are fluid mosaics of lipids and proteins. Membrane structure results in selective permeability. Passive transport is diffusion of a substance across a membrane with no energy investment. Active transport uses energy to move solutes against their gradients. Bulk transport across the plasma membrane occurs by exocytosis and endocytosis
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
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
Integral Proteins
A transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane and with 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 Proteins
A protein loosely bound to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer
Glycolipids
A lipid with one or more covalently attached carbohydrates
Glycoproteins
A protein with one or more covalently attached carbohydrates
Transport Proteins
A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane
Aquaporins
A channel protein in a cellular membrane that specifically facilitates osmosis, the diffusion of free water across the membrane
Diffusion
The random thermal motion of particles of liquid, gases, or solids. In the presence of a concentration or electrochemical gradient, it 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 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 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 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
Lacking turgor (stiffness or firmness), as in a plant cell in surroundings where there is a tendency for water to leave the cell. (A walled cell becomes this if it has a higher water potential than its surroundings, resulting in the loss of water)
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 Channels
A transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient
Gated Channels
A transmembrane protein channel that opens or closes in response to a particular stimuli
