Sodium-Potassium Pump, Diffusion, and Electrochemical Gradients (Lecture Notes)

Vocabulary flashcards covering key concepts from the lecture: Na+/K+ pump, diffusion, electrochemical gradients, membrane structure, and nerve signaling.

Sodium-potassium pump (Na+/K+ ATPase)

Membrane protein that uses ATP to exchange 3 Na+ out of the cell for 2 K+ into the cell, establishing and maintaining the electrochemical gradient and resting membrane potential.

Ion

An electrically charged atom or molecule; cations are positively charged and anions are negatively charged (e.g., Na+ and K+ are cations).

ATP

Adenosine triphosphate; the energy-carrying molecule that powers pumps like Na+/K+ by driving their conformational change.

Active transport

Movement of substances across a membrane against their concentration gradient, requiring energy (as with the Na+/K+ pump).

Diffusion

Passive movement of particles from regions of high concentration to regions of low concentration; no energy input required.

Osmosis

Diffusion of water across a semipermeable membrane from areas of lower solute concentration to higher solute concentration.

Electrochemical gradient

The combined effect of chemical (concentration) and electrical (charge) gradients that drives ion movement across membranes.

Concentration gradient

A difference in solute concentration between two regions; substances tend to move from high to low along this gradient.

Electrical gradient

A voltage difference across a membrane that attracts or repels ions of a given charge.

Membrane potential

Voltage difference across a cell membrane resulting from ion distribution and membrane permeability.

Resting membrane potential

Baseline membrane potential when a cell is not firing (often about -70 mV in neurons).

Na+ ion

Sodium ion; positively charged (+1) and moves according to chemical and electrical gradients.

K+ ion

Potassium ion; positively charged (+1); tends to move out by concentration gradient, while the electrical gradient pulls it inward.

Phospholipid bilayer

Two-layer membrane with polar (hydrophilic) heads and nonpolar (hydrophobic) tails; forms a barrier to ions.

Hydrophobic region

Nonpolar tails of phospholipids in the bilayer that repel water and polar molecules.

Hydrophilic region

Polar heads of phospholipids that interact with water on either side of the membrane.

Protein structure–function relationship

A protein’s three-dimensional shape (determined by its amino acid sequence) determines its transport or signaling function.

Conformational change

A shape change in a protein (often ATP-driven) that enables its function, such as moving ions across a membrane.

Sodium channel

A membrane pore that allows Na+ to diffuse passively when open, contributing to action potentials.

Potassium channel

A membrane pore that allows K+ to diffuse passively; movement depends on concentration and electrical gradients.

Stoichiometry of Na+/K+ pump

Per cycle: 3 Na+ are pumped out and 2 K+ are pumped in.

Electrical gradient in signaling

An ion-driven potential that primes cells (e.g., nerve cells) for action potentials by existing gradients.

Nerve impulse (electrochemical impulse)

Propagation of a signal via rapid, coordinated ion movements across membranes, not a simple electrical current.

Channel vs pump

Channels allow passive diffusion along gradients; pumps expend energy to move ions against gradients and maintain gradients.

Cell-energy budget for pumps

In some cells, Na+/K+ pumps consume a large portion of ATP, sometimes >50% of cellular energy.

Equilibrium in diffusion

A state where opposing gradients balance, resulting in no net ion movement.