Martini Chapter 3 – Cells, Membranes & Transport

Vocabulary flashcards covering key terms and definitions related to cell theory, plasma membrane structure, membrane proteins, permeability, and passive, active, and vesicular transport processes from Martini Chapter 3.

Cell Theory

States that cells are the basic building blocks of all organisms, the smallest units that perform vital functions, arise only from pre-existing cells, and each cell maintains its own homeostasis.

Plasma Membrane

A thin phospholipid bilayer that surrounds every cell, separating cytoplasm from the extracellular environment.

Functions of the Plasma Membrane

Physical isolation, regulation of exchange with the environment, sensitivity to the environment, and structural support.

Components of the Plasma Membrane

Phospholipid bilayer, cholesterol, membrane proteins, and carbohydrate extensions (glycoproteins/glycolipids) that form the glycocalyx.

Integral Protein

Membrane protein embedded within or spanning the lipid bilayer; difficult to remove and often forms channels or carriers.

Peripheral Protein

Protein attached loosely to the inner or outer surface of the membrane; easily separated and often functions as an enzyme or anchor.

Anchoring Protein

Membrane protein that stabilizes a cell by attaching it to the cytoskeleton or to neighboring cells.

Recognition Protein

Glycoprotein that identifies a cell as self or non-self to the immune system.

Membrane-bound Enzyme

Protein catalyst anchored in the membrane that speeds specific chemical reactions at the cell surface.

Receptor Protein

Membrane protein that binds a specific ligand to trigger a cellular response.

Transporter (Carrier Protein)

Membrane protein that binds specific solutes and moves them across the membrane, usually by changing shape.

Ion Channel

Protein tunnel in the membrane that allows ions to cross down their electrochemical gradient.

Leak Channel

Ion channel that is always open, permitting continuous passive ion flow.

Gated Channel

Ion channel that opens or closes in response to specific stimuli.

Voltage-Gated Channel

Gated ion channel that opens or closes when membrane potential changes.

Chemically (Ligand)-Gated Channel

Gated ion channel that responds to the binding of a specific chemical messenger.

Mechanically Gated Channel

Gated ion channel that opens in response to physical distortion of the membrane (pressure, stretch).

Membrane Permeability

The ease with which substances can cross the membrane, influenced by size, charge, lipid solubility, and presence of channels or carriers.

Simple Diffusion

Passive movement of molecules from an area of higher to lower concentration directly through the lipid bilayer.

Facilitated Diffusion

Passive transport in which a carrier protein or channel helps a specific substance cross the membrane down its concentration gradient.

Osmosis

Passive diffusion of water across a selectively permeable membrane toward the solution with the higher solute concentration.

Tonicity

Effect of a solute concentration on the shape of a cell; describes solutions as isotonic, hypotonic, or hypertonic.

Active Transport

Energy-requiring movement of substances across a membrane against their concentration gradient.

Primary Active Transport

Active transport that directly uses ATP to move ions or molecules, e.g., the Na⁺/K⁺ pump.

Secondary Active Transport

Transport that uses the energy stored in an ion gradient (created by primary active transport) to move a different substance against its gradient.

Vesicular Transport

Bulk movement of materials into or out of the cell inside membrane-bound sacs (vesicles), requiring ATP.

Receptor-Mediated Endocytosis

Highly selective uptake of molecules using receptors and clathrin-coated vesicles.

Pinocytosis

“Cell drinking”; nonspecific uptake of extracellular fluid and dissolved solutes via small vesicles.

Phagocytosis

“Cell eating”; ingestion of large particles or microbes into phagosomes by specialized cells.

Exocytosis

Vesicular process that fuses intracellular vesicles with the plasma membrane to release contents outside the cell.