Biomembranes and Cell Architecture

Vocabulary terms and definitions covering prokaryotic and eukaryotic cell architecture, lipid bilayer properties, membrane proteins, transport mechanisms, and organelle functions.

Amphipathic

Molecules, such as phosphoglycerides, sphingolipids, and cholesterol, that possess both a polar (hydrophilic) head group and a hydrophobic tail.

Phosphoglyceride

The most abundant class of lipids in biomembranes, consisting of a hydrophobic tail with two fatty acyl chains esterified to glycerol phosphate and a polar head group.

Sphingolipids

Lipids consisting of a hydrophobic tail made of a long-chain fatty acid attached to the amino group of sphingosine (an amino alcohol) and a polar head group.

Cholesterol

A lipid with a basic structure of a four-ring hydrocarbon and a hydroxyl substituent; it is too hydrophobic to form a bilayer alone and is not found in prokaryotic cells.

Saturation

A term applied to fatty acid constituents depending on whether they contain carbon-carbon double bonds; commonly containing 16 or 18 carbons with 0, 1, or 2 double bonds.

Liposome

A spontaneously formed lipid structure consisting of a phospholipid bilayer that serves as a model for biological membranes.

Integral membrane proteins

Also called transmembrane proteins, these span a phospholipid bilayer and are composed of three segments (exoplasmic face, cytosolic face, and a membrane-spanning segment).

Lipid-anchored membrane proteins

Proteins covalently bound to one or more lipid molecules, where the hydrophobic carbon chain of the lipid is embedded in one leaflet of the membrane.

Peripheral membrane proteins

Proteins that do not interact with the hydrophobic core; they bind indirectly via integral proteins or directly to lipid head groups to support the membrane or resist tension.

Fluid Mosaic Model

A model describing the plasma membrane structure, including components like glycoproteins, glycolipids, cholesterol, and various proteins within a fluid bilayer.

FRAP (Fluorescence Recovery After Photobleaching)

A technique using laser light to quantify the lateral movements of specific plasma-membrane proteins and lipids.

Net flux

The condition where the movement of a substance into a cell (influx) and out of the cell (efflux) is not balanced, meaning one exceeds the other.

Simple diffusion

A passive mechanism where solute molecules move through the lipid bilayer or through an aqueous protein channel.

Facilitated diffusion

Protein-mediated movement of substances down a concentration gradient, such as glucose transport via the GluT1 transporter.

Active transport

The movement of substances against a concentration gradient requiring an energy-driven protein "pump" and ATP.

Endocytosis

A process used by large polar molecules that cannot pass through the hydrophobic plasma membrane by passive means.

Mitochondria

Double-membrane organelles that generate ATP by the oxidation of glucose and fatty acids; they contain a matrix with ribosomes, tRNA, and mitochondrial DNA.

Lysosomes

Organelles with an acidic lumen that degrade internalized material and worn-out cellular membranes or organelles via phagocytic, endocytic, or autophagic pathways.

Nuclear envelope

A double membrane enclosing the nucleus; the outer membrane is continuous with the rough endoplasmic reticulum.

Nucleolus

A nuclear subcompartment specifically responsible for the synthesis of most of the cell's rRNA.

Smooth Endoplasmic Reticulum (ER)

An organelle that synthesizes lipids and detoxifies certain hydrophobic compounds.

Rough Endoplasmic Reticulum (ER)

An organelle functioning in the synthesis, processing, and sorting of secreted proteins, lysosomal proteins, and certain membrane proteins.

Golgi complex

An organelle that processes and sorts secreted, lysosomal, and membrane proteins synthesized on the rough ER.

Vacuole

An organelle that stores water, ions, and nutrients, degrades macromolecules, and facilitates cell elongation during growth.

Chloroplasts

Double-membrane organelles containing internal membrane-bounded sacs that carry out photosynthesis.