Cell Structure & Function: Membrane Transport

Vocabulary flashcards covering cellular membrane structure, passive and active transport mechanisms, ion channels, uniporters, cotransporters, and ATP pumps based on lecture material.

Fluid mosaic model

A structural model describing cell membranes as dynamic bilayers composed of asymmetrically distributed lipids and proteins.

Passive transport

The movement of molecules down their concentration gradient from high concentration to low concentration without requiring energy.

Active transport

The movement of molecules against their concentration gradient from low concentration to high concentration, which requires energy.

Ion channel

A protein complex forming a selective open pore through the bilayer that allows ions to flow passively down their concentration gradient at high rates ($10^7-10^8\text{ ions/s}$).

Voltage-gated channel

A gated ion channel whose opening is controlled by a change in membrane potential.

Ligand-gated channel

A gated channel whose opening is controlled by the binding of a chemical ligand, often referred to as a receptor.

Stretch activated channel

A gated channel whose opening is controlled by a change in membrane tension.

Uniporter

A carrier protein (transporter) that passively moves a single type of substrate down its concentration gradient via conformational changes at rates of $10^2-10^4\text{ molecules/s}$.

Facilitated diffusion

Passive, selective membrane transport mediated by carrier proteins or uniporters through conformational changes without requiring energy.

GLUT1

A specific glucose uniporter protein expressed in erythrocytes that undergoes substrate-triggered conformational changes to transport glucose.

GLUT2

A high-capacity, low-affinity glucose transporter encoded by a distinct gene and expressed in liver cells.

Cotransporter

A membrane transporter that moves two or more different substances simultaneously, utilizing the energy from one molecule moving down its gradient to transport another against its gradient.

Secondary active transport

Active transport driven by coupling the passive movement of one substance down its concentration gradient to the movement of another substance against its concentration gradient.

Symporter

A cotransporter that moves two or more different substances across the membrane in the same direction.

Antiporter

A cotransporter that moves two or more different substances across the membrane in opposite directions.

ATP pump

A transporter that directly consumes ATP as an energy source to transport substances against their concentration gradient at rates of $10^0-10^3\text{ ions/s}$.