Transport Across Membranes: Overcoming the Permeability Barrier

Flashcards covering key vocabulary related to molecule transport across cell membranes, including concepts like concentration gradients, membrane potentials, and different types of diffusion and active transport, along with relevant proteins and biological examples.

Concentration gradient

The difference in the concentration of a substance between two areas (ex: in/out of a membrane).

Electrochemical potential (Electrical gradient)

The difference in the electrical charge of a substance between two areas; charged particles want to move toward the opposite charge.

Membrane potential

The voltage (charge difference) across the cell membrane, due to ion distribution.

Ion

An atom with a charge (it must have lost or gained electrons).

Anion

A negatively charged ion.

Cation

A positively charged ion.

Simple diffusion

The movement of molecules directly across a membrane, from an area of high to low concentration, without energy and without a protein channel.

Osmosis

The movement of water from high to low water concentration across a differentially permeable membrane.

Hypertonic solution

An environment that is more concentrated than the cell, causing the cell to shrink.

Hypotonic solution

An environment that is less concentrated than the cell, causing the cell to swell.

Isotonic solution

An environment with the same concentration as the cell, resulting in no net movement of water.

Turgor pressure

The pressure of water inside a plant cell pushing against the cell wall.

Plasmolysis

Shrinkage of the cell membrane, usually caused by water loss.

Facilitated diffusion

Diffusion through a protein channel from high to low concentration, considered passive transport.

Carrier proteins

A type of transport protein in the cell membrane that binds to a specific molecule, undergoes a shape change, and releases the molecule on the other side.

Uniport

A subtype of carrier protein that moves a single type of molecule in one direction across the membrane.

GLUT1 transporter

A specific uniport carrier protein that carries D-glucose into or out of the cell.

Antiport

A subtype of carrier protein that moves two different molecules in two different directions across the membrane.

Symport

A subtype of carrier protein that moves two different molecules in the same direction together across the membrane.

Anion Exchange Protein (Band 3 Protein)

A protein found in the plasma membrane of RBCs that exchanges bicarbonate (HCO₃⁻) for chloride (Cl⁻) across the membrane, functioning as an antiporter.

Channel proteins

A type of membrane protein that forms pores or tunnels through a cell membrane, allowing specific molecules to move through.

Ion Channel

A type of channel protein that selectively allows ions to pass.

Aquaporins

A type of channel protein that transports water faster than simple diffusion.

Porins

A type of channel protein that forms large, relatively non-selective barrels to transport many small molecules (sugars, ions, amino acids), found in the plasma membrane of many cell types.

Active transport

The movement of molecules across a membrane against their concentration or electrochemical gradient, which requires energy.

Direct (Primary) Active Transport

Active transport where a transport protein (ATPase enzyme) uses ATP hydrolysis directly to move molecules against their gradient.

Na/K pump

A protein that uses ATP to pump 3 Na+ ions out of the cell and 2 K+ ions into the cell, creating an strong electrochemical gradient; an example of direct active transport and an antiporter.

Indirect (Secondary) Active Transport

Active transport that uses the energy released by one molecule moving with its concentration or electrochemical gradient to drive another molecule to move against its gradient.

Cystic Fibrosis

A genetic disease caused by mutations in the CFTR gene, leading to a dysfunctional channel protein that normally moves chloride ions out of cells, resulting in thick, sticky mucus.

CFTR gene

The gene mutated in cystic fibrosis, which codes for a channel protein responsible for moving chloride ions out of cells.

Bacteriorhodopsin proton pump

A protein found in certain members of archaea that pumps protons (H+) out of the cell when it absorbs light.