BIOL 3030 – Biomembrane Structure - LEC 3 - Stevens

Vocabulary flashcards covering the major terms and definitions from BIOL 3030 Lecture 3 on biomembrane structure.

Biomembrane

A dynamic, selectively permeable barrier composed mainly of lipids and proteins that separates cellular compartments and regulates transport.

Fluid Mosaic Model

Concept describing biomembranes as two-dimensional fluids where lipids and proteins move laterally within a mosaic of assorted components.

Exoplasmic Face

The leaflet of a membrane that faces the cell exterior or the lumens of organelles.

Cytosolic Face

The leaflet of a membrane that faces the cytosol.

Amphipathic Molecule

Chemical species, such as most membrane lipids, that contain both hydrophobic and hydrophilic regions.

Phospholipid

The primary lipid of all cell membranes, consisting of a glycerol (or sphingosine) backbone, two hydrophobic acyl tails, and a hydrophilic phosphate-based head group.

Micelle

Spherical aggregate of amphipathic molecules with hydrophobic tails inward and polar heads outward; common in digestion.

Liposome

Artificial, closed phospholipid bilayer vesicle used to study membranes or deliver drugs.

Phosphoglyceride

Class of phospholipids built on a glycerol backbone; abundant in eukaryotic and prokaryotic membranes.

Sphingolipid

Membrane lipid with a sphingosine backbone; includes sphingomyelin and glycolipids and is enriched in neural tissue.

Sterol

Four-ring lipid (e.g., cholesterol) that modulates membrane fluidity and serves as a precursor for hormones and bile.

Cholesterol (Membrane Orientation)

Sterol inserted with its small hydroxyl group near phospholipid head groups and rings/tail buried in the hydrophobic core.

Fatty Acid Saturation

Degree of double bonding in acyl chains; more saturation and longer chains decrease membrane fluidity.

Fluorescence Recovery After Photobleaching (FRAP)

Technique that measures the lateral mobility of lipids or proteins by monitoring fluorescence return after a bleached spot recovers.

Lateral Diffusion

Rapid, side-to-side movement of lipids/proteins within one leaflet; occurs ~10⁷ exchanges per second.

Flip-Flop

Rare, energetically unfavorable trans-leaflet movement of lipids; usually requires flippase enzymes.

Membrane Fluidity

Viscous property of the bilayer influenced by temperature, lipid composition, and cholesterol content.

Lipid Raft

Cholesterol- and sphingolipid-rich microdomain that concentrates certain proteins and facilitates signal transduction.

Integral (Transmembrane) Protein

Protein that spans the bilayer with one or more hydrophobic membrane-spanning segments.

Transmembrane Domain

Hydrophobic α-helix or β-barrel segment of a protein that crosses the lipid bilayer.

Single-Pass Protein

Integral protein that crosses the membrane once (e.g., glycophorin A).

Multipass Protein

Integral protein with multiple membrane-spanning segments; includes seven-pass GPCRs.

G-Protein-Coupled Receptor (GPCR)

Large family of seven-helix multipass proteins that transmit extracellular signals via G proteins.

Aquaporin

Multipass channel protein that facilitates rapid, selective water transport across membranes.

Porin (β-Barrel)

Channel protein formed by a β-barrel; found in bacterial, mitochondrial, and chloroplast outer membranes.

Lipid-Anchored Protein

Protein covalently attached to a lipid moiety that embeds in the membrane while the polypeptide remains outside the bilayer.

Peripheral Membrane Protein

Protein bound non-covalently to membrane surfaces or to integral/lipid-anchored proteins; easily released by mild treatments.

Glycosylation

Covalent addition of carbohydrate chains to proteins; occurs on exoplasmic domains and is crucial for cell–cell interactions.

Glycoprotein

Protein with attached oligosaccharide chains; includes ABO blood group antigens.

GPI Anchor

Glycosylphosphatidylinositol lipid anchor that tethers certain proteins to the exoplasmic leaflet.

Flippase

ATP-powered enzyme that translocates specific phospholipids between membrane leaflets, generating asymmetry.

Membrane Asymmetry

Unequal distribution of lipids between leaflets; important for signaling, apoptosis, and membrane stability.

Annular Phospholipid

Lipid molecule that transiently and specifically associates with the surface of a membrane protein.

Membrane Thickness

Distance between leaflet head groups; varies (≈3.5–5.6 nm) with lipid composition and influences protein localization.

Membrane Curvature

Bending of the bilayer driven by asymmetric lipid distribution (e.g., small-head PE) and protein scaffolds; essential for vesicle formation.

Selective Permeability

Property allowing certain molecules to cross the membrane more readily than others.

Self-Healing

Ability of disrupted bilayers to spontaneously reseal due to hydrophobic forces.

Signal Transduction

Process by which membranes and associated proteins transmit external or internal signals into cellular responses.