Structure of Biological Membranes and Function of Membrane Proteins

Vocabulary practice flashcards covering membrane structure, phospholipid types, bilayer asymmetry, transbilayer transporters, and membrane protein classifications based on lecture notes.

Plasma Membrane

A selectively permeable boundary composed of lipids and proteins that defines the cell surface, remaining impermeable to large molecules like proteins and nucleic acids while permeable to small molecules like ions and metabolites.

Phosphatidylethanolamine (PE)

A glycerol-based phospholipid consisting of an ethanolamine head group, phosphate, glycerol, and two fatty acid tails; it is zwitterionic and enriched on the cytoplasmic side of the membrane.

Amphipathic

Describing a molecule that possesses both hydrophilic (polar or charged) and hydrophobic (nonpolar) regions.

Zwitterionic

Describing a molecule containing both positive and negative charges, resulting in a net charge of zero.

Leaflet

One of the two individual single-layer halves (either interior/cytoplasmic or exterior/extracellular) that form a phospholipid bilayer.

Phosphatidylcholine (PC)

A zwitterionic, choline-containing glycerol-based phospholipid enriched on the extracellular side of the plasma membrane.

Phosphatidylserine (PS)

An amine-containing glycerol-based phospholipid with a net negative charge that is enriched on the cytoplasmic side of the plasma membrane.

Cholesterol

A membrane lipid characterized by a small polar head ($-OH$ group) and a nonpolar hydrocarbon backbone that stiffens the membrane and can flip easily between leaflets.

Lipid Rafts

Membrane microdomains enriched in sphingolipids and cholesterol that allow proteins to "ride along" with moving phospholipids, enabling faster changes in protein localization.

Transbilayer Asymmetry

The unequal phospholipid composition between the two leaflets of a membrane, where choline-containing lipids (PC and sphingolipids) are enriched on the extracellular side and amine-containing lipids (PS and PE) are enriched on the cytoplasmic side.

Flippase

An ATP-dependent transbilayer transporter that moves specific phospholipids, such as phosphatidylserine (PS), from the outer (extracellular) leaflet to the inner (cytoplasmic) leaflet against their concentration gradient.

Floppase

An ATP-dependent transbilayer transporter that moves phospholipids, such as phosphatidylcholine (PC) and cholesterol, from the inner (cytoplasmic) leaflet to the outer (extracellular) leaflet against their concentration gradient.

Integral Membrane Proteins

Proteins embedded within (spanning or non-spanning) or covalently attached to the lipid bilayer, often featuring membrane-spanning $\begin{array}{c}\alpha\end{array}$-helical domains of about $20$ hydrophobic amino acids.

Peripheral Membrane Proteins

Proteins attached non-covalently to integral membrane proteins or to phospholipid head groups through electrostatic or hydrophobic interactions.

Integrins

Cell-matrix adhesion integral membrane proteins that form physical contacts with the surrounding extracellular matrix.

Cadherins

$Ca^{2+}$-dependent cell-cell adhesion molecules that attach neighboring cells to each other.

Neural Cell Adhesion Molecules (N-CAMs)

$Ca^{2+}$-independent cell-cell adhesion integral membrane proteins that attach neighboring cells to each other.

Ankyrin

A peripheral membrane protein on the intracellular side that anchors the spectrin-actin submembranous cytoskeleton meshwork to integral membrane proteins.