Cell Membrane Structure and Transport Mechanisms

Comprehensive vocabulary flashcards covering membrane structure, the fluid mosaic model, transport mechanisms (passive, active, facilitated), and bulk transport processes.

Selective Permeability

The ability of cell membranes to regulate the passage of substances across them, allowing some molecules to cross more easily than others.

Passive Transport

The transport of a molecule that does not require energy from the cell because the solute moves with its concentration or electrochemical gradient.

Diffusion

The passive movement of substances down their concentration gradient from an area of high concentration to an area of low concentration.

Osmosis

The diffusion of water down its concentration gradient across a selectively permeable membrane, moving from areas of low solute concentration to areas of high solute concentration.

Facilitated Diffusion

The passive diffusion of molecules or ions across a membrane via transport proteins down their concentration gradient without requiring cellular energy.

Channel Proteins

Transport proteins that provide a hydrophilic channel allowing specific molecules and ions to pass through the cell membrane.

Gated Channels

A class of channel proteins that only allow passage of substances through the membrane in response to a stimulus.

Aquaporins

Specialized protein channels that facilitate the rapid passage of water molecules across the cell membrane.

Carrier Proteins

Transport proteins that undergo conformational changes to allow substances to pass and move across the membrane.

Phospholipid Bilayer

A double layer formed by phospholipids with hydrophilic phosphate heads oriented towards the aqueous environments and hydrophobic tails facing inward away from aqueous environments.

Amphipathic

A molecule that contains both hydrophilic and hydrophobic sections, such as phospholipids and integral membrane proteins.

Fluid Mosaic Model

A structural model describing cell membranes as dynamic structures held together by weak hydrophobic interactions that allow components to move and shift, composed of a mosaic of diverse molecules.

Unsaturated Hydrocarbon Tails

Kinked lipid tails that prevent the tight packing of phospholipids, thereby maintaining membrane fluidity at low temperatures.

Cholesterol (in cell membranes)

A membrane lipid that reduces phospholipid movement at high temperatures to prevent excessive fluidity, and reduces tight packing at low temperatures to prevent the membrane from solidifying.

Integral Proteins

Amphipathic transmembrane proteins that are embedded into the lipid bilayer, making contact with both hydrophilic and hydrophobic parts of the membrane.

Peripheral Proteins

Proteins loosely bonded to the membrane surface that do not interact with the hydrophobic tails of the phospholipid bilayer.

Glycolipids

Carbohydrates bonded to phospholipids on the membrane surface that serve as markers for cell-to-cell recognition to defend the body against foreign invaders.

Glycoproteins

The most abundant cell-surface recognition molecules, composed of carbohydrates bonded to proteins that function as markers for cell-to-cell recognition.

Oligosaccharides

Short sugar chains located on the external surface of the plasma membrane used as cell markers.

Cell Wall

An extracellular structure in plant cells composed of cellulose that covers the plasma membrane to provide shape, structure, protection, and regulation of water intake.

Plasmodesmata

Hole-like structures in the plant cell wall filled with cytosol that connect adjacent cells.

Active Transport

Transport of a molecule that requires cellular energy because it moves a substance against its concentration gradient.

Adenosine Triphosphate (ATP)

The cellular energy currency that transfers its terminal phosphate group to a transport protein, inducing a conformational change to drive active transport.

Membrane Potential

An electrical charge across the plasma membrane resulting from unequal concentrations of ions, where the cytoplasm is relatively negative compared to the extracellular fluid.

Electrogenic Pumps

Transport proteins that generate voltage across a membrane by pumping ions, storing energy in electrochemical gradients for cellular processes.

Sodium-Potassium Pump

An electrogenic pump in animal cells that pumps $3\text{ Na}^+$ out of the cell and $2\text{ K}^+$ into the cell, resulting in a net charge of $+1$ to the extracellular fluid.

Proton Pump

An integral membrane protein found in plants, fungi, and bacteria that pumps $H^+$ out of the cell to build up a proton gradient across the membrane.

Cotransport

The coupling of the favorable downhill diffusion of one substance with the unfavorable uphill movement of another substance against its concentration gradient.

Sucrose-$H^+$ Cotransporter

A plant transport mechanism that transports sucrose into a cell against its concentration gradient coupled with $H^+$ diffusing down its electrochemical gradient.

Exocytosis

The secretion of large molecules via vesicles that fuse to the plasma membrane and release their contents into the extracellular fluid.

Endocytosis

The uptake of molecules and materials into the cell through vesicles formed from the inward pinching of the plasma membrane.

Phagocytosis

A form of endocytosis in which a cell engulfs large particles using pseudopodia, packages them into a food vacuole, and fuses with a lysosome for digestion.

Pinocytosis

Nonspecific uptake of extracellular fluid containing dissolved molecules packaged into protein-coated vesicles to be digested by the cell.

Receptor-Mediated Endocytosis

The specific uptake of molecules when target solutes bind to plasma membrane receptors, prompting them to cluster and form a coated vesicle to import large quantities.