Cell Membrane: Lipid Composition and Membrane Proteins

Vocabulary flashcards covering plasma membrane structure, lipids, proteins, and glycocalyx based on lecture notes.

Phospholipids

Amphipathic lipids that form the plasma membrane bilayer; hydrophilic heads face aqueous environments and hydrophobic tails face inward.

Cholesterol

Sterol intercalated in the lipid bilayer that modulates membrane fluidity and stiffness and participates in lipid raft formation.

Glycolipids

Lipids with carbohydrate chains located mainly on the outer leaflet; contribute to cell recognition and surface charge.

Glycoproteins

Proteins with attached carbohydrate chains; extracellular portions are glycosylated and contribute to the glycocalyx.

Integral membrane proteins

Proteins embedded in the lipid bilayer, often spanning it (transmembrane), with alpha-helical segments.

Peripheral membrane proteins

Proteins attached to the membrane surface by protein–protein interactions; do not cross the bilayer.

Lipid rafts

Cholesterol- and glycosphingolipid-rich membrane microdomains that are thicker and less fluid and concentrate signaling proteins.

Glycocalyx

Carbohydrate-rich layer on the cell surface formed by glycoproteins and glycolipids; cushions, mediates recognition and adhesion.

Sialic acid

Terminal acidic sugar residues on glycoproteins and glycolipids that impart a negative charge to the membrane.

Outer leaflet lipids

Phosphatidylcholine, sphingomyelin, and phosphatidylethanolamine enriched in the outer leaflet.

Inner leaflet lipids

Phosphatidylserine, phosphatidylinositol, and phosphatidylethanolamine enriched on the cytosolic face and carry negative charge.

Phosphatidylserine

Negatively charged phospholipid predominantly on the inner leaflet; involved in signaling.

Phosphatidylinositol

Negatively charged phospholipid on the inner leaflet; key signaling lipid.

Phosphatidylethanolamine

Phospholipid mainly on the inner leaflet; contributes to membrane curvature and structure.

Phosphatidylcholine

Major phospholipid of the outer leaflet; provides membrane structure.

Sphingomyelin

Outer leaflet sphingolipid contributing to lipid order and membrane structure.

Unit membrane

A histology term for the plasma membrane: two dense lines separated by a lucent layer, about 7.5–10 nm thick.

Transmembrane protein

An integral membrane protein that spans the bilayer, often with multiple alpha-helical spans.

Ion channels

Membrane proteins forming pores that selectively allow ions to pass down electrochemical gradients.

Na+/K+ pump

ATP-driven transporter that exchanges Na+ for K+ to maintain ion gradients and resting potential.

Receptors

Membrane proteins that bind extracellular ligands and trigger intracellular signaling.

Enzymes (membrane-bound)

Proteins anchored in the membrane that catalyze reactions at or near the membrane.

Pinocytotic vesicle

Vesicle formed during pinocytosis for nonspecific uptake of extracellular fluid.

Coated vesicle

Vesicle with a protein coat (e.g., clathrin) involved in endocytosis and trafficking.

Phagosome

Vesicle containing a phagocytosed particle; fuses with lysosomes for degradation.