Cell Membrane Structure and Function Flashcards

A complete glossary of vocabulary terms, concepts, and structures related to cell membrane biology based on the transcript.

Cell membrane

A biological membrane (also known as plasma membrane, cytoplasmic membrane, or historically as plasmalemma) that separates and protects the interior of a cell from the extracellular space.

Integral proteins

Membrane proteins that span the lipid bilayer and serve as membrane transporters, ion channels, proton pumps, or receptors.

Peripheral proteins

Proteins attached to the surface of the cell membrane that act as enzymes to facilitate interactions with the cell's environment.

Homeoviscous adaptation

The ability of some organisms to regulate the fluidity of their cell membranes by altering their lipid composition.

Liquid crystalline state

The state of phospholipid molecules in the cell membrane under physiological conditions in which lipid molecules are free to diffuse and exhibit rapid lateral diffusion.

Annular lipid shell

A fraction of membrane lipid in direct contact with integral membrane proteins that is tightly bound to the protein surface and behaves as part of the protein complex.

Liposomes

Approximately spherical pockets enclosed by a lipid bilayer, formed by suspending lipids in an aqueous solution and agitating the mixture through sonication.

Glycocalyx

A carbohydrate layer on the extracellular surface of the plasma membrane with a penultimate sugar of galactose and a terminal sugar of sialic acid.

G-protein coupled receptor

A single polypeptide chain that crosses the lipid bilayer seven times responding to signal molecules such as hormones and neurotransmitters.

Endocytosis

An active transport process in which cells absorb molecules by engulfing them through inward membrane invaginations that pinch off to form vesicles.

Exocytosis

An active transport process in which the membrane of an intracellular vesicle fuses with the plasma membrane to extrude its contents into the extracellular medium.

Fluid mosaic model

The membrane model proposed by S. J. Singer and G. L. Nicolson in $1972$ describing biological membranes as a two-dimensional liquid in which lipid and protein molecules diffuse.

Apical membrane

The surface of the plasma membrane of a polarized cell that faces inward to the lumen (also called luminal membrane).

Basolateral membrane

The surface of the plasma membrane of a polarized cell that forms its basal and lateral surfaces, facing outward toward the interstitium.

Endosymbiotic theory

The theory proposing that mitochondria and chloroplasts evolved from ancient bacteria (such as Paracoccus, Rhodopseudomonas, and cyanobacteria) engulfed by eukaryotic cells.

Sarcolemma

The specialized cell membrane of muscle cells that contains T-tubules and has an average thickness of $10\,m$ compared to the $4\,m$ thickness of a general cell membrane.

Oolemma

The cell membrane of an oocyte that lacks a lipid bilayer and consists of an inner fertilization envelope and an exterior zona pellucida made of glycoproteins.

Axolemma

The specialized plasma membrane on the axons of nerve cells responsible for generating action potentials and interacting with spectrin and actin.

Porins

Pore-forming membrane proteins present in the outer membrane of gram-negative bacteria that impart a porous quality to the membrane.

Permeability

The rate of passive diffusion of molecules (permeants) through a membrane, which depends mainly on electric charge and polarity, and to a lesser extent on molar mass.