Biological Membranes and the Cell Surface


Membrane Functions
  • Form specialized compartments by selective permeability
    • Unique environment
    • Creation of concentration gradients
    • pH and charge (electrical, ionic) differences
  • Asymmetric protein distribution
  • Cell-Cell recognition
  • Site for receptor molecule biding for cell signaling
    • Receptor binds ligand (such as a hormone)
    • Induces intracellular reactions
  • Controls and regulates reaction sequences
    • Product of one enzyme is the substrate for the next enzyme
    • Can "line up" the enzymes in the proper sequence

Membrane Structure According to the Fluid Mosaic Model of Singer and Nicolson


  • The membrane is a fluid mosaic of phospholipids and proteins
  • Two main categories of membrane proteins - integral and peripheral
    • Peripheral proteins - bound to the surface of the membrane
    • Integral proteins - permeate the surface of the membrane
  • Membrane regions differ in protein configuration and concentration
    • Outside vs. inside - different peripheral proteins
    • Proteins only exposed to one surface
    • Proteins extend completely through - exposed to both surfaces
    • Membrane lipid layer fluid
      • Proteins move laterally along membrane



Membrane Lipids

Bilayer Formation

Membrane Fluidity

How Cells Regulate Membrane Fluidity

Membrane Carbohydrates - Glycolipids and Glycoproteins

Membrane Proteins


An Example - Asymetry of Intestinal Epithelial Cell Membranes


The Extracellular Matrix (ECM) and Plant Cell Walls

Cell to Cell Attachments

Tight Junctions and Desmosomes

Cell Gaps

Plasmodesmata & Gap Junctions

Cell Communication

In multi-cellular organism, cells can communicate via chemical messenger

Three Stages of Cellular Communication

No matter where they are located, signal receptors have several general characteristics

Two Methods of Cell-Cell Communication