Regulation of Membrane Transport

Vocabulary flashcards reviewing key concepts, transport mechanisms, channels, active/passive transport, glucose transport, and drug movement from Module 2, Lecture 2 on Regulation of Membrane Transport.

Plasma Membrane

A selectively permeable barrier between the cell and the extracellular environment that allows the cell to maintain a constant internal environment.

Passive Transport

The movement of molecules across a biological membrane along, down, or with their concentration gradient without requiring direct energy expenditure.

Active Transport

The movement of molecules across biological membranes against their concentration gradient, requiring energy from ATP hydrolysis directly or indirectly.

Osmosis

The passage of water across a semi-permeable membrane from an area of higher water concentration to an area of lower water concentration (or low solute concentration to high solute concentration).

Aquaporins

Membrane channel proteins that specifically allow for the movement of water across biological membranes.

Isotonic Solution

A solution in which there is no net movement of water into or out of the cell, resulting in unchanged cell volume.

Hypotonic Solution

A solution in which the net movement of water is into the cell, causing cell volume to increase and potentially causing cells to burst.

Hypertonic Solution

A solution in which the net movement of water is out of the cell, causing cell volume to decrease.

Ion Channels

Membrane proteins structured so that hydrophilic amino acid residues form a protected pathway for ions to pass through the hydrophobic core of the phospholipid bilayer.

$$K_m$$

The solute concentration that yields half of the maximum rate of solute transport ($\frac{1}{2} V_{\max}$), reflecting the transporter's binding affinity for the solute.

$$V_{\max}$$

The maximum rate of transport achieved when a membrane transporter becomes completely saturated with solute.

Primary Active Transport

A transport process where energy derived directly from ATP hydrolysis is used to move molecules across a membrane against their electrochemical gradient.

$$\text{Na}^+/\text{K}^+\text{-ATPase}$$

A P-class primary active transport enzyme that uses energy from ATP hydrolysis to pump $3\,\text{Na}^+$ ions out of the cell and $2\,\text{K}^+$ ions into the cell against their electrochemical gradients per cycle.

Secondary Active Transport

A cotransport process driven by ion gradients created by primary active transport, moving a solute against its gradient without direct ATP hydrolysis by the cotransporter itself.

Uniporter

A transport protein that facilitates the passive movement of a single type of molecule across the membrane along its concentration gradient.

Symporter

A secondary active cotransporter that moves two different substrates in the same direction across the plasma membrane.

Antiporter

A secondary active cotransporter that transports one substrate into the cell while simultaneously transporting another substrate out of the cell in opposite directions.

P-class Transporters

A class of active transport proteins that directly hydrolyze ATP to transport ions such as $\text{H}^+$, $\text{Na}^+$, $\text{K}^+$, and $\text{Ca}^{2+}$ across membranes.

ABC Transporters

ATP-binding cassette transporters, a class of active transport proteins responsible for moving ions, drugs, and xenobiotics across biological membranes.

Insulin-Insensitive Glucose Transport

Facilitated diffusion of glucose mediated by GLUT uniporters that are continuously present on the surface of cell types such as erythrocytes, leukocytes, hepatocytes, brain cells, and eye cells.

Insulin-Sensitive Glucose Transport

Glucose transport in skeletal muscle cells and adipocytes where insulin signaling recruits GLUT uniporters from an intracellular pool to the plasma membrane.

SGLT (Sodium-Glucose Symporter)

A secondary active cotransporter located on the apical membrane of intestinal epithelial cells, proximal convoluted tubules of the kidney, and choroid plexus that transports glucose against its concentration gradient coupled with sodium moving down its concentration gradient.

Blood-Brain Barrier

A specialized physiological barrier consisting of tight junctions between endothelial cells that limits drug passage into the central nervous system.