The movement of a substance across a cell membrane, with an expenditure of energy, against its concentration or electrochemical gradient; mediated by specific transport proteins.
Having both a hydrophilic region and a hydrophobic region
A channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis.
A region along which the density of a chemical substance increases or decreases.
The spontaneous movement of a substance down its concentration gradient, from a region where it is more concentrated to a region where it is less concentrated.
The diffusion gradient of an ion, which is affected by both the concentration difference of the ion across a membrane and the ion's tendency to move relative to the membrane potential.
An ion transport protein that generates voltage across a membrane.
Cellular uptake of biological molecules and particulate matter via formation of new vesicles from the plasma membrane.
The cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane.
The spontaneous passage of molecules or ions across a biological membrane with the assistance of specific transmembrane transport proteins.
Limp. Lacking in stiffness or firmness, as in a plant cell in surroundings where there is no tendency for water to enter the cell.
A transmembrane protein channel that opens or closes in response to a particular stimulus.
An extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch.
A lipid with covalently attached carbohydrate(s).
A protein with one or more carbohydrates covalently attached to it.
Referring to a solution that, when surrounding a cell, will cause the cell to lose water.
Referring to a solution that, when surrounding a cell, will cause the cell to take up water.
Typically 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 either side of the membrane (or lining the channel in the case of a channel protein).
A transmembrane protein channel that allows a specific ion to flow across the membrane down its concentration gradient.
Referring to a solution that, when surrounding a cell, has no effect on the passage of water into or out of the cell.
A molecule that binds specifically to another molecule, usually a larger one.
low-density lipoprotein (LDL)
A particle in the blood made up of cholesterol and other lipids surrounded by a single layer of phospholipids in which proteins are embedded.
The difference in electrical charge (voltage) across a cell's plasma membrane due to the differential distribution of ions. It affects the activity of excitable cells and the transmembrane movement of all charged substances.
A type of protein filament that acts as a motor protein with actin filaments to cause cell contraction.
Regulation of solute concentrations and water balance by a cell or organism.
The diffusion of water across a selectively permeable membrane.
The diffusion of a substance across a biological membrane with no expenditure of energy.
A protein loosely bound to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer.
A type of endocytosis in which large particulate substances are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells).
A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.
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.
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.
The movement of specific molecules into a cell by the inward budding of membranous vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.
A property of biological membranes that allows them to regulate the passage of substances.
A transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell.
The ability of a solution surrounding a cell to cause that cell to gain or lose water.
A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.
Swollen or distended, as in plant cells. (A walled cell becomes this if it has a greater solute concentration than its surroundings, resulting in entry of water.)