U4- Transport Across Cell Membrane: Structure of the Cell Membrane

Vocabulary practice flashcards covering Section 4.1: Structure of the Cell Membrane, including phospholipids, membrane proteins, lipids, and their functions.

Phospholipid Bilayer

The structure making up half of the cell membrane, composed of two layers of phospholipids with hydrophobic tails pointing inward and hydrophilic heads pointing outward.

Hydrophobic Tails

The fatty acid tails of phospholipids that face inward toward each other in the bilayer, allowing other components with hydrophobic regions to float in the membrane.

Hydrophilic Heads

The water-attracting portions of phospholipids that point outward toward the exterior and interior watery environments of the cell.

Low Viscosity (Membrane)

A characteristic of membrane phospholipids that allows the cell membrane to behave dynamically like a fluid.

Channel Protein

A membrane protein that creates an open passage allowing materials to flow passively through the cell membrane without requiring energy.

Carrier Protein

A membrane protein that actively pumps materials across the cell membrane.

Glycoprotein

A membrane protein with attached carbohydrates that is used in cell-to-cell communication.

Glycolipid

A membrane lipid with attached carbohydrates that functions as a receptor and provides anchors for other structures.

Cholesterol

A lipid component of the cell membrane that regulates bilayer fluidity, preventing it from becoming too viscous or too fluid.

Cell Membrane Structure Diagram

A model illustrating the phospholipid bilayer embedded with proteins, cholesterol molecules, glycoproteins, and glycolipids.

Fluid Mosaic Model

A structural representation describing the cell membrane as a flexible matrix of lipids embedded with proteins that float freely within the plane of the layer.

Amphipathic

A chemical characteristic describing molecules that possess both water-loving polar regions and water-fearing nonpolar regions.

Selective Permeability

A functional property of biological barriers allowing certain uncharged or nonpolar solutes to pass while blocking large or charged molecules.

Integral Protein

A membrane-spanning molecule embedded permanently within the hydrophobic core of the phospholipid bilayer.

Peripheral Protein

A surface-bound polypeptide loosely associated with either the inner or outer leaflet of the phospholipid bilayer without penetrating the hydrophobic core.

Simple Diffusion

The unassisted passive movement of small, nonpolar solutes across a lipid barrier down their concentration gradient.

Facilitated Diffusion

The passive translocation of ions or polar solutes across a biological membrane via specialized transmembrane channels or carriers.

Osmosis

The spontaneous net movement of water molecules through a semipermeable membrane toward an area of higher solute concentration.

Aquaporin

A specialized membrane channel protein that selectively increases the rate of water transport across the plasma membrane.

Active Transport

The movement of ions or chemical species against an electrochemical gradient, powered directly or indirectly by metabolic energy.

Passive Transport

The cellular transport of substances down an electrochemical gradient without the consumption of biochemical energy.

Concentration Gradient

A gradual difference in the solute abundance per unit volume between two regions across a boundary.

Endocytosis

An active cellular uptake mechanism in which the plasma membrane invaginates to engulf extracellular substances into vesicles.

Exocytosis

The intracellular process by which secretory vesicles fuse with the outer lipid barrier to discharge their cargo into the extracellular space.

Hypertonic Solution

An external medium with a higher solute concentration than the cytosol, leading to net water outflow and cellular shrinkage.

Hypotonic Solution

An external medium with a lower solute concentration than the cytosol, resulting in water influx and cellular swelling or lysis.

Isotonic Solution

An external medium having an equivalent effective osmolarity to the cytosol, producing zero net water flux across the membrane.

Primary Active Transport

A direct energy-requiring mechanism that uses ATP hydrolysis to pump ions across a biological membrane against their chemical gradients.

Secondary Active Transport

The movement of a solute against its gradient coupled to the downhill flow of a co-transported ion established by an electrochemical potential difference.

Electrochemical Gradient

The combined influence of an electrical potential difference and a chemical concentration difference acting on an ion across a membrane.

Bulk Transport

The energy-dependent cellular mechanism that moves large macromolecules or volumes of fluid across the plasma membrane using vesicles.

Phagocytosis

A specific form of endocytosis in which a cell engulfs large particulate matter, microorganisms, or cellular debris.

Pinocytosis

A subtype of endocytosis involving the non-specific ingestion of extracellular fluids and dissolved solutes.

Receptor-Mediated Endocytosis

A highly selective vesicle-forming pathway triggered when specific extracellular target molecules bind to designated surface proteins.

Sodium-Potassium Pump

A transmembrane primary active transport protein that expels three $Na^+$ ions and imports two $K^+$ ions per hydrolyzed molecule of ATP.

Cytoskeletal Filaments

Internal protein fibers anchored to the cytoplasmic face of membrane proteins that provide structural support and anchor embedded molecules.

Glycocalyx

A carbohydrate-enriched outer coating formed by surface glycoproteins and glycolipids that aids in cellular recognition and protection.

Turgor Pressure

The internal hydrostatic force exerted outward against the rigid cell wall by water accumulation in a hypotonic environment.

Plasmolysis

The cellular process in plant cells where the plasma membrane and interior contents pull away from the cell wall due to water loss in a hypertonic medium.

Crenation

The shriveling and scalloping of animal erythrocytes caused by the net osmotic outflow of water in a hypertonic solution.