Transporters, Pumps & Channels - Definitions

Electrolyte

an ion such as Na⁺, K⁺, Cl⁻, HCO₃⁻, or Ca²⁺.

Impermeant anion

a negatively charged substance that does not readily cross the plasma membrane, such as proteins or nucleic acids.

Plasma membrane

membrane separating intracellular and extracellular environments and regulating movement of substances between them.

Phospholipid bilayer

the primary structural framework of the plasma membrane and its hydrophobic barrier.

Concentration gradient

a difference in concentration between two regions that influences the direction of passive solute movement.

Simple passive diffusion

movement of a substance across the membrane down its concentration gradient without energy expenditure.

Hydrophobic barrier

the lipid portion of the membrane that restricts passage of most charged and polar substances.

Ion channel

membrane protein that permits passive movement of ions down their concentration/electrochemical gradient.

Ligand-gated channel

ion channel regulated by binding of a ligand.

Voltage-gated channel

ion channel regulated by changes in membrane voltage.

Leak channel

channel that allows passive ion movement without requiring a ligand or voltage change to open it.

Stretch-activated channel

channel regulated by mechanical stretching.

Carrier protein

membrane protein that binds a specific solute and changes conformation to move it across the membrane.

Facilitated transport

carrier-protein-mediated transport that can facilitate either passive or active movement.

Facilitated diffusion

protein-mediated passive movement of a solute down its gradient without ATP.

Primary active transport

transport that uses ATP directly to move substances against their electrochemical gradients.

Na⁺/K⁺-ATPase

primary active transporter that moves 3 Na⁺ out of the cell and 2 K⁺ into the cell using 1 ATP per cycle.

Secondary active transport

transport that uses energy stored in an ion gradient established by primary active transport.

Cotransporter

carrier that transports multiple substances together, using movement of one substance to drive movement of another.

Electrogenic pump

pump that produces a net movement of electrical charge across the membrane.