Structure of Biological Membranes

Fluid Mosaic Model

A dynamic structure ~8 nm thick with proteins floating in a lipid sea.

Fatty Acids and Fluidity

Saturated fatty acids allow tighter packing; unsaturated fatty acids increase membrane fluidity.

Cholesterol Function

It regulates fluidity, stabilizing at high temperatures and preventing crystallization at low temperatures.

Integral Membrane Proteins

Proteins that span the entire membrane, partially embedded, containing both hydrophobic and hydrophilic regions.

Peripheral Membrane Proteins

Lack surface hydrophobic groups (do not penetrate the phospholipid

bilayer)Have polar or charged regions that interact with exposed membrane

proteins or polar heads of phospholipids. Found on both sides of the membrane.

Anchored Membrane Proteins

Proteins covalently bound to hydrophobic lipid components that tether them in the bilayer.

Membrane Carbohydrates

Found on the outer surface to serve as recognition sites and signals.

Homotypic vs. Heterotypic Binding

Homotypic occurs between identical molecules; heterotypic occurs between different molecules.

Cell Junctions

Tight junctions, desmosomes, and gap junctions.

glycolipid

a carbohydrate covalently bound to a lipid; recognition signal for interactions between cells

glycoprotein

one or more short carbohydrate (oligosaccharide of 20 monosaccharides) chains covalently bound to a protein; cell recognition and adhesion

Proteoglycan

contains numerous long polysaccharides; cell recognition and adhesion

Sponge reagregation

cells adhere to other cell, eventually forming a colony of a new sponge.

long saturated acids

allows for tighter packing = less fluid

Unsaturated fatty acids

membrane less dense = more fluid

membrane proteins

transport, energy metabolism, anchor cytoskeleton signaling,

Membrane and proteins interact non-covalently

tight junctions

form a “quilted” seal, barring the movement of dissolved materials through the space between epithelial cells

desmosomal adhesion

link adjacent ells tightly but permit materials to move around them in intercellular space

Gap junctions

let adjacent cells communicate