Biomembrane Structure and Function

Vocabulary flashcards covering key concepts, terms, and components discussed in the biomembrane lecture notes.

Biomembrane

A biological membrane surrounding cells and organelles, formed by a fluid phospholipid bilayer with embedded and associated proteins; serves as a selective barrier and functional interface.

Phospholipid bilayer

Two layers of phospholipids forming the core structure of membranes; hydrophilic heads face water, hydrophobic tails face inward.

Plasma membrane

The outermost biomembrane of the cell, separating the cell’s interior from the environment.

Hydrophilic head group

The polar, water-attracting region of a phospholipid that contains a phosphate-containing group.

Hydrophobic tail

The nonpolar fatty acid tails of a phospholipid that avoid water.

Fluid mosaic model

The concept that membranes are fluid, dynamic mixtures of lipids and proteins that diffuse laterally.

Overton

Ernest Overton’s 1895 idea that membranes are lipid-impregnated boundaries; early barrier concept for biomembranes.

Lipid bilayer self-assembly

Phospholipids spontaneously form bilayers in water, with hydrophobic tails inward and heads outward.

Amphipathic

Molecules with both hydrophilic (water-loving) and hydrophobic (water-fearing) regions.

Cholesterol

A sterol lipid intercalated in membranes that modulates fluidity by spacing phospholipids; distribution varies by membrane type.

Saturated fatty acid

A fatty acid with no double bonds; tends to pack tightly and decrease membrane fluidity.

Unsaturated fatty acid

A fatty acid with one or more double bonds; creates bends that increase membrane fluidity.

Outer leaflet

The phospholipid layer of the bilayer facing the exterior of the cell or organelle.

Inner leaflet

The phospholipid layer facing the interior cytoplasm or matrix of an organelle.

Membrane asymmetry

Different lipid or protein composition between the outer and inner leaflets of a membrane.

Transmembrane protein

A protein that spans the entire lipid bilayer, often forming channels or receptors; can be single-pass or multipass.

Single-pass alpha helix

Transmembrane protein with one helical segment crossing the membrane.

Multipass alpha helix

Transmembrane protein with multiple helices crossing the membrane, potentially forming a pore.

Beta barrel

Transmembrane pore formed by beta-strands arranged in a barrel, common in bacterial membranes and organelles.

Integral protein

A membrane protein embedded within the lipid bilayer, often spanning the membrane.

Peripheral membrane protein

A protein associated with the membrane surface, often via lipid anchors or interactions with other proteins.

Glycoprotein

Membrane protein with carbohydrate (glycan) chains attached to specific amino acids.

Glycocalyx

Carbohydrate-rich coating on the cell surface formed by glycoproteins and glycolipids; involved in protection, signaling, and immune interactions.

Glycolipid

Lipid with carbohydrate groups attached; contributes to cell recognition and membrane structure.

Phosphatidylcholine (PC)

A common phospholipid with a choline head group, often enriched in the outer leaflet.

Phosphatidylethanolamine (PE)

A phospholipid with an ethanolamine head group; often enriched in the inner leaflet.

Phosphatidylserine (PS)

A phospholipid with a serine head group; negatively charged and enriched on the inner leaflet.

Lipid rafts

Membrane microdomains enriched in cholesterol and sphingolipids that organize signaling and trafficking.

FRAP (fluorescence recovery after photobleaching)

A technique to measure lateral mobility of lipids or proteins in membranes by bleaching and observing recovery.

Anthotrophic/amphitrophic proteins

Proteins with affinity for both lipid environments and aqueous environments; can associate with membranes under certain conditions.

Liposome

A vesicle formed from a phospholipid bilayer; used to deliver drugs and study membrane properties.

Micelle

A spherical aggregate formed by amphipathic lipids with a single layer, not a bilayer; used for drug delivery in some contexts.

Glycerol backbone

Backbone of phospholipids derived from glycerol to which fatty acids and a phosphate-containing head group are attached.

Phospholipid head groups

Groups like phosphate, choline, ethanolamine, and serine that form the polar head of phospholipids.

Sphingolipids

A class of lipids with a sphingosine backbone; important components of membranes, often involved in signaling.

Glycolipids

Lipids with carbohydrate groups attached; contribute to cell recognition and membrane structure.

Cholesterol’s role in membranes

Intercalates between phospholipids to modulate fluidity and permeability, influencing membrane stiffness.

Permeability barrier

The membrane’s function to regulate which substances enter or leave the cell or organelle.

Membrane protein localization

Proteins can be oriented to function on either the outer or inner leaflet depending on their role and structure.