Plasma Membrane – Vocabulary Review

Vocabulary flashcards summarizing key terms about plasma membrane structure, function, and associated proteins from the lecture notes.

Plasma Membrane

A phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates that forms a semi-permeable barrier between intracellular and extracellular fluid.

Phospholipid Bilayer

Double layer of phospholipids whose hydrophilic heads face fluid and hydrophobic tails face inward, creating the membrane’s selective barrier.

Selective Permeability

Property of the plasma membrane that allows small, non-polar molecules to pass freely while restricting large or charged substances without assistance.

Intracellular Fluid (ICF)

Fluid compartment inside the cell, separated from extracellular fluid by the plasma membrane.

Extracellular Fluid (ECF)

Fluid outside the cell; the plasma membrane controls exchange between ECF and ICF.

Hydrophilic Head

Charged phosphate group of a phospholipid that is attracted to water and faces the aqueous environment.

Hydrophobic Tail

Non-charged lipid chains of a phospholipid that repel water and form the membrane’s internal barrier to polar molecules.

Integral (Transmembrane) Protein

Protein that spans the bilayer and can act as channels, transporters, enzymes, receptors, or adhesion molecules.

Channel Protein

Transmembrane protein forming a selective pore; once open, small molecules or ions move rapidly down their gradients.

Transporter (Carrier) Protein

Transmembrane protein that binds a specific substrate, changes shape, and moves it across the membrane without a continuous pore.

Na⁺ Channel

Selective ion channel that allows sodium ions to flow quickly into or out of the cell when gated open.

Na⁺/K⁺ Pump

Active transporter that uses ATP to move 3 Na⁺ out of the cell and 2 K⁺ into the cell, maintaining ionic gradients.

Membrane Enzyme

Protein embedded in the plasma membrane that catalyzes chemical reactions at the cell surface.

Membrane Receptor

Protein that binds extracellular signals (ligands) and initiates intracellular responses.

Cell Surface Marker

Membrane protein or carbohydrate tag that identifies a cell’s type or state to other cells.

Cell Adhesion Molecule (CAM)

Surface protein that binds cells to each other or to the extracellular matrix, stabilizing tissues.

Integrin

CAM that connects cells to the extracellular matrix and transduces signals across the membrane.

Cadherin

Calcium-dependent CAM that anchors cells to each other, especially in desmosomes.

Selectin

CAM involved in transient cell–cell adhesion, notably in the immune and vascular systems.

Immunoglobulin Superfamily (IgSF)

Group of CAMs with immunoglobulin-like domains that mediate cell adhesion and recognition.

Desmosome

Cell-to-cell junction where CAMs anchor neighboring cells, preventing overstretching of tissue.

Tight Junction

Seal formed by small proteins that weld adjacent cell membranes together, preventing leakage between cells.

Gap Junction

Connection of adjacent cells via connexon protein tunnels that directly link cytoplasm for rapid communication.

Cell Polarity

Spatial separation of cellular regions (apical vs. basal) that enables directional transport across cell layers.

Apical Surface

The ‘top’ side of a polarized cell facing the external environment or lumen.

Basal Surface

The ‘bottom’ side of a polarized cell attached to underlying tissue, facing away from the lumen.