(3.2) cell transport

Comprehensive vocabulary flashcards covering passive and active cell transport mechanisms, membrane proteins, and vesicle-mediated transport from Biology 189.

Passive transport

The movement of substances across a cell membrane from high to low concentration without using cellular energy.

Active transport

The movement of substances across a cell membrane from low to high concentration, requiring energy in the form of $\text{ATP}$.

Simple diffusion

The direct, unassisted movement of small, nonpolar molecules (like $CO_2$ and $O_2$) through the lipid membrane from high to low concentration.

Facilitated diffusion

The passive movement of polar or charged molecules across the membrane with the assistance of transport proteins.

Channel protein

A transmembrane tunnel with an open pore that allows specific ions or small molecules to quickly flow down their gradient.

Carrier protein

A membrane transport protein that binds a specific substance and changes shape to move it across the lipid bilayer.

Aquaporin

A specialized membrane channel dedicated to rapid water transport, conducting up to $3 \times 10^9\,\text{molecules per second}$.

Primary active transport

The movement of substances against their concentration gradient directly powered by the breakdown of $\text{ATP}$.

Secondary active transport

The movement of a substance against its gradient driven by the downhill flow of a cotransported ion rather than direct $\text{ATP}$ use.

Proton pump

A membrane transport protein that uses $\text{ATP}$ to pump $H^+$ ions across the membrane, generating a voltage and pH gradient.

$Na^+/K^+$ pump

A membrane transport protein that uses $\text{ATP}$ to pump three sodium ions out of the cell and two potassium ions into the cell.

$H^+$/sucrose cotransporter

A membrane protein that uses the favorable return flow of hydrogen ions to pull sugar into the cell against its gradient.

Endocytosis

A bulk transport process where the plasma membrane folds inward to bring materials into the cell inside vesicles.

Phagocytosis

"Cellular eating"—a bulk uptake process where the cell extends pseudopodia to engulf and digest large particles or microbes.

Pinocytosis

"Cellular drinking"—a bulk uptake process where the cell folds inward to take in droplets of extracellular fluid and dissolved solutes.

Receptor-mediated endocytosis

A selective import process where specific target molecules (like cholesterol) bind to membrane surface proteins before being taken inside.

Exocytosis

A bulk transport process where internal vesicles fuse with the plasma membrane to export materials out of the cell.

ACE2 (Angiotensin-converting enzyme 2)

A cell-surface protein that the virus SARS-CoV-2 binds to in order to enter host cells.