Membranes

• Compartmentalization

• Create gradients

• Enzyme activity

• Signal transduction

• Selective passage

Purpose

Composition: Lipids

Phospholipids

Sphingolipids

Sterols

Composition: Proteins

• Integral/transmembrane

• Peripheral – often lipid anchored

Composition:

CarbohydratesOn external surface: glycoproteins & glycolipids

Figure 1.5 Early membrane models

Fluid Mosaic Model

-Singer & Nicolson (1972) describe integral proteins, lateral diffusion of lipids and limited transverse diffusion

Figure 1.6 The freeze-fracture

technique reveals “bumps” in the

membrane interior.

Figure 1.7 The Fluid Mosaic Model proposed by Singer and Nicolson

Paradigm shift: Lipid Rafts

-Certain domains within the bilayer are not as 'fluid' and are enriched with proteins (some are anchoring), cholesterol and sphingolipids -Signaling domains

3° dimension

• Asymmetry of

membrane

• Interacts with

substances at the

border

• Cytoskeleton