Cell Bio - Chapter 11: Cell Membrane Structure and Function

Flashcards for reviewing cell membrane structure and function, based on lecture notes.

Plasma Membrane

The container that holds the self-reproducing system of molecules inside a living cell, separating and protecting its chemical components from the outside environment. It is a protein-studded, fatty film.

Lipid Bilayer

A two-ply sheet of lipid molecules, about 5 nm thick, into which proteins are inserted. It serves as a permeability barrier to most water-soluble molecules in cell membranes.

Membrane Proteins

Carry out most membrane functions, including transport, sensing, and acting as receptors. Give different membranes their individual characteristics.

Selective Channels and Transporters

Proteins that penetrate the plasma membrane, allowing specific small molecules and ions to be imported and exported.

Receptors

Proteins in the plasma membrane that enable the cell to receive information about changes in its environment and respond appropriately.

Internal Membranes

Enclose intracellular compartments in eukaryotic cells, forming organelles like the endoplasmic reticulum, Golgi apparatus, and mitochondria.

Amphipathic

Molecules with both hydrophilic (water-loving) and hydrophobic (water-fearing) parts. Membrane lipids, like phospholipids, cholesterol, and glycolipids, are amphipathic.

Hydrophilic

Water-loving molecules that dissolve readily in water due to charged or polar groups that can form electrostatic attractions or hydrogen bonds with water.

Hydrophobic

Water-fearing molecules that are insoluble in water because they are uncharged and nonpolar, and therefore cannot form favorable interactions with water molecules.

Liposomes

Closed, spherical vesicles formed by pure phospholipids when added to water, ranging in size from 25 nm to 1 mm in diameter. Used to study lipid bilayer movements.

Flip-flop

The tumbling of a phospholipid molecule from one half of the bilayer to the other, which is a rare event without the help of proteins.

Lateral Diffusion

The rapid exchange of places between lipid molecules and their neighbors within the same monolayer, allowing lipids to diffuse a significant length within the membrane.

Unsaturated Hydrocarbon Tails

Hydrocarbon tails with one or more double bonds, creating kinks that make it more difficult for the tails to pack against one another, thus increasing membrane fluidity.

Saturated Hydrocarbon Tails

Hydrocarbon tails with no double bonds and a full complement of hydrogen atoms, allowing them to pack tightly and decrease membrane fluidity.

Cholesterol

A sterol found in animal cell membranes that modulates membrane fluidity by filling the spaces between phospholipid molecules, stiffening the bilayer and making it less flexible and permeable.

Scramblases

Enzymes that remove randomly selected phospholipids from one half of the lipid bilayer and insert them in the other, redistributing phospholipids equally between each monolayer of the ER membrane.

Flippases

Enzymes in the Golgi membrane that remove specific phospholipids from the side of the bilayer facing the exterior space and flip them into the monolayer that faces the cytosol, creating membrane asymmetry.

Glycolipids

Lipids located mainly in the plasma membrane, and only in the noncytosolic half of the bilayer. Their sugar groups face the cell exterior, forming part of the glycocalyx.

Glycocalyx

The sugar coating formed by the carbohydrate portions of glycolipids, glycoproteins and proteoglycans on the exterior of the cell. Protects the cell surface and enables cell-cell recognition.

Transmembrane Proteins

Proteins that extend through the lipid bilayer, with part of their mass on either side. They are amphipathic, having both hydrophobic and hydrophilic regions.

Integral Membrane Proteins

Proteins that are directly attached to the lipid bilayer and can only be removed by disrupting the bilayer with detergents.

Peripheral Membrane Proteins

Proteins that are not directly attached to the lipid bilayer and can be released from the membrane by gentle extraction procedures.

Detergents

Small, amphipathic, lipid-like molecules that destroy the lipid bilayer by disrupting hydrophobic associations, used to solubilize membrane proteins. They aggregate into micelles.

Cell Cortex

A meshwork of fibrous proteins, like spectrin, attached to the underside of the plasma membrane in animal cells to provide support and maintain cell shape.

Membrane Domains

Functionally specialized regions on the cell or organelle surface where particular proteins are confined within the bilayer membrane.

Tight Junctions

Specialized junctional proteins that form a continuous belt around epithelial cells, creating a seal between adjacent plasma membranes and preventing membrane proteins from diffusing past the junction.

Lectins

Proteins specialized to bind to particular oligosaccharide side chains on glycoproteins and glycolipids, mediating cell-cell recognition and adhesion.