Membrane Structure and Transport

Flashcards reviewing plasma membrane structure, fluidity, components, and passive/active transport mechanisms.

Plasma Membrane

The boundary that separates the living cell from its surroundings, exhibiting selective permeability.

Selective Permeability

The property of a cellular membrane that allows some substances to cross it more easily than others.

Amphipathic

Describing a molecule, such as a phospholipid, that contains both hydrophobic and hydrophilic regions.

Fluid Mosaic Model

A model stating that a membrane is a fluid structure with a mosaic of various proteins embedded in a phospholipid bilayer.

Hugh Davson and James Danielli

Scientists who in 1935 proposed a sandwich model where the phospholipid bilayer lies between two layers of globular proteins.

S. J. Singer and G. Nicolson

Scientists who proposed the fluid mosaic model in 1972, stating membrane proteins are dispersed within the bilayer with hydrophilic regions exposed to water.

Freeze-fracture

A specialized preparation technique that splits a membrane along the middle of the phospholipid bilayer to reveal protein distribution.

Peripheral Proteins

Membrane proteins that are bound exclusively to the surface of the plasma membrane.

Integral Proteins

Membrane proteins that penetrate the hydrophobic core of the phospholipid bilayer.

Transmembrane Proteins

Integral proteins that completely span across the cell membrane.

Glycolipids

Molecules formed when membrane carbohydrates are covalently bonded to lipids.

Glycoproteins

Molecules formed when membrane carbohydrates are covalently bonded to proteins.

Aquaporins

Channel proteins that specifically facilitate the rapid passage of water molecules across biological membranes.

Channel Proteins

Transport proteins with a hydrophilic channel that specific molecules or ions use as a tunnel through the membrane.

Carrier Proteins

Transport proteins that bind to specific molecules and undergo a change in shape to shuttle them across the membrane.

Diffusion

The tendency for molecules to spread out evenly into available space down their concentration gradient.

Passive Transport

The diffusion of a substance across a biological membrane down its concentration gradient requiring no energy expenditure by the cell.

Osmosis

The diffusion of water across a selectively permeable membrane from lower solute concentration to higher solute concentration.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water.

Isotonic Solution

A solution in which solute concentration is equal to that inside the cell, resulting in no net water movement.

Hypertonic Solution

A solution in which solute concentration is greater than inside the cell, causing the cell to lose water.

Hypotonic Solution

A solution in which solute concentration is less than inside the cell, causing the cell to gain water.

Osmoregulation

The control of solute concentrations and water balance necessary for organism survival in hypertonic or hypotonic environments.

Plasmolysis

A lethal effect in plant cells placed in a hypertonic environment where the plasma membrane shrinks away from the cell wall.

Facilitated Diffusion

The passive transport of molecules across a plasma membrane aided by transport proteins like channel or carrier proteins.

Active Transport

The movement of solutes across a membrane against their concentration gradients, requiring energy input typically in the form of ATP.

Sodium-Potassium Pump

A major active transport electrogenic pump in animal cells that moves sodium ions out and potassium ions into the cell using ATP.

Membrane Potential

The voltage difference across a biological membrane generated by the unequal distribution of positive and negative ions.

Electrochemical Gradient

The combined chemical concentration gradient and electrical force driving the passive movement of ions across a membrane.

Electrogenic Pump

A transport protein that generates voltage across a membrane by pumping charged ions.

Proton Pump

The primary electrogenic pump of plants, fungi, and bacteria that actively transports hydrogen ions ($\text{H}^+$) out of the cell.

Exocytosis

A form of bulk transport where intracellular transport vesicles migrate to and fuse with the plasma membrane to release contents outside.

Endocytosis

A form of bulk transport where the cell takes in macromolecules by forming new vesicles from the plasma membrane.

Phagocytosis

A type of endocytosis commonly referred to as cellular eating, where a cell engulfs large particles or whole cells into a vacuole.

Pinocytosis

A type of endocytosis known as cellular drinking, where extracellular fluid is continuously gulped into tiny vesicles.

Receptor-Mediated Endocytosis

A specific type of endocytosis where ligand binding to surface receptors triggers targeted vesicle formation.

Ligand

Any molecule that binds specifically to a receptor site of another molecule.