Lesson 14: Membrane Transport Key Terms

membrane transport protein

membrane protein that mediates the passage of ions or molecules across a membrane. The two main classes are transporters (also called carriers or permeases) and channel

transporter

membrane transport protein that binds to a solute and transports it across the membrane by undergoing a series of conformational changes. Can either transport ions or molecules passively down an electrochemical gradient or they can link the conformational changes to a source of metabolic energy such as ATP hydrolysis to drive active transport

channel

transmembrane protein complex that allows inorganic ions or other small molecules to diffuse passively across the lipid bilayer

passive transport

transport of a solute across a membrane down its concentration gradient or its electrochemical gradient, using only the energy stored in the gradient

electrochemical gradient

combined influence of a difference in the concentration of an ion on two sides of a membrane and the electrical charge difference across the membrane (membrane potential). Ions or charged molecules can move passively only down their own electrochemical gradient

active transport

movement of a molecule across a membrane or other barrier driven by energy other than that stored in the electrochemical or concentration gradient of the transported molecule itself

uniporter

carrier protein that transports a single solute from one side of the membrane to the other

symporter

carrier protein that transports two types of solute across the membrane in the same direction

antiporter

carrier protein that transports two different ions or small molecules across a membrane in opposite directions, either simultaneously or in sequence

transcellular transport

transport of solute, such as nutrients, across an epithelium, by means of membrane transport proteins in the apical and basal faces of the epithelial cells

ATPase

an enzyme that breaks down ATP (adenosine triphosphate) to release usable energy

V-type proton pump

turbine-like protein machines constructed from multiple different subunits that use the energy of ATP hydrolysis to drive transport across a membrane, transfers H+ into organelles such as lysosomes to acidify their interior

F-type ATP synthase

membrane protein complex that uses a proton gradient to make ATP

Na+ K+ pump

transmembrane carrier protein found in the plasma membrane of most animal cells that pumps Na+ out of and K+ into the cell, using energy derived from ATP hydrolysis

aquaporins

channel protein embedded in the plasma membrane that greatly increases the cell’s permeability to water, allowing transport of water, but not ions, at a high rate across the membrane