One of a large family of membrane transport proteins characterized by a highly conserved ATP binding domain.
action potential
Nerve impulses that travel along axons.
active transport
The transport of molecules in an energetically unfavorable direction across a membrane coupled to the hydrolysis ofATP or other source of energy.
antiport
The transport of two molecules in opposite directions across a membrane.
apical domain
The exposed free surface of a polarized epithelial cell.
aquaporin
A channel protein through which water is able to rapidly cross the plasma membrane.
basolateral domain
The surface region of a polarized epithelial cell that is in contact with adjacent cells or the extracellular matrix.
carrier protein
A protein that selectively binds and transports small molecules across a membrane.
caveolae
Small invaginations of the plasma membrane that may be involved in endocytosis.
caveolin
A protein that interacts with lipid rafts and forms caveolae.
channel protein
A protein that forms pores through a membrane.
cholesterol
A lipid consisting of four hydrocarbon rings. Cholesterol is a major constituent of animal cell plasma membranes and the precursor of steroid hormones.
clathrin-coated pit
A specialized region of the plasma membrane that contains receptors for macromolecules to be taken up by endocytosis.
clathrin-coated vesicle
A transport vesicle coated with clathrin.
dynamin
A membrane-associated GTPase involved in vesicle budding.
endocytosis
The uptake of extracellular material in vesicles formed from the plasma membrane.
endosome
A vesicular compartment involved in the sorting and transport to lysosomes of material taken up by endocytosis.
facilitated diffusion
The transport of molecules across a membrane by carrier or channel proteins.
fluid mosaic model
A model of membrane structure in which proteins are inserted in a fluid phospholipid bilayer.
fluid-phase endocytosis
The nonselective uptake of extracellular fluids during endocytosis.
glycocalyx
A carbohydrate coat covering the cell surface.
glycolipid
A lipid consisting of two hydrocarbon chains linked to a polar head group containing carbohydrates.
glycosylphosphatidylinositol (GPI) anchor
A glycolipid containing phosphatidylinositol that anchors proteins to the external face of the plasma membrane.
integral membrane protein
A protein embedded within the lipid bilayer of cell membranes.
ion channel
A protein that mediates the rapid passage of ions across a membrane by forming open pores through the phospholipid bilayer.
ion pump
A protein that couples ATP hydrolysis to the transport of ions across a membrane.
ligand
A molecule that binds to a receptor.
ligand-gated channel
An ion channel that opens in response to the binding of signaling molecules.
lipid raft
A discrete plasma membrane domain formed as a cluster of cholesterol and sphingolipids.
low-density lipoprotein (LDL)
A lipoprotein particle that transports cholesterol in the circulation.
macropinocytosis
The uptake of fluids in large vesicles.
Na+-K+ ATPase
See Na+-K+ pump.
Na+-K+ pump
An ion pump that transports Na+ out of the cell and K+ into the cell.
Nernst equation
The relationship between ion concentration and membrane potential.
passive diffusion
The diffusion of small hydrophobic molecules through a phospholipid bilayer.
patch clamp technique
A method used to isolate and study the activity of single ion channels.
peripheral membrane protein
A protein that is indirectly associated with cell membranes by protein-protein interactions.
phagocytosis
The uptake of large particles, such as bacteria, by a cell.
phagolysosome
A lysosome that has fused with a phagosome or autophagosome.
phagosome
A vacuole containing a particle taken up by phagocytosis.
phosphatidylcholine
A glycerol phospholipid with a head group formed from choline.
phosphatidylethanolamine
A glycerol phospholipid with a head group formed from ethanolamine.
phosphatidylinositol
A glycerol phospholipid with a head group formed from inositol.
phosphatidylserine
A glycerol phospholipid with a head group formed from serine.
pinocytosis
The uptake of fluids or molecules into a cell by small vesicles.
porin
A member of a class of proteins that cross membranes as β-barrels and form channels in the outer membranes of some bacteria, mitochondria, and chloroplasts.
receptor down-regulation
The loss of receptors from the cell surface as a result of their internalization by endocytosis following ligand binding.
receptor-mediated endocytosis
The selective uptake of macromolecules that bind to cell surface receptors that concentrate in clathrin-coated pits.
selectin
A type of cell adhesion molecule that recognizes oligosaccharides exposed on the cell surface.
sphingomyelin
A phospholipid consisting of two hydrocarbon chains bound to a polar head group containing serine.
symport
The transport of two molecules in the same direction across a membrane.
transcytosis
The sorting and transport of proteins to different domains of the plasma membrane following endocytosis.
transmembrane protein
An integral membrane protein that spans the lipid bilayer and has portions exposed on both sides of the membrane.
uniport
The transport of a single molecule across a membrane.
voltage-gated channel
An ion channel that opens in response to changes in electric potential.
