Roles of membranes in cells:

• Filter

• Protection - from pH, salinity, temperature, etc

• Compartmentalization - separating functions

Fluid Mosaic Model

• Fluid: not rigid, molecules are free to move. Pieces of membrane can be removed then reattached.

• Mosaic: composed of many diff molecules:

  • Phospholipids: arranged in a bi-layer due amphiphilic nature, may have attached carbs that function in the region: glyco-lipid

  • Cholesterol: create space between phospholipids and increase fluidity

  • Proteins: Add function. On surface or trans-membrane, may have attached: glyco-proteins

Membrane Proteins:

• Transport: move materials across the membrane

• Enzyme: catalyze a reaction at membrane surface

• Signal/Receptor, Triggering signals: sit on exterior until something interesting comes by and lunges at it, causes biochemical cascade → chain of reaction (guards reacting at intruder/passerby)

• Attachment & Recognition/ Anchor: attachment point for cytoskeleton of other cells or recognition of chemical environment, blood recognizers

• Integral: impeded in bi-layer, has hydrophobic region to interact w interior of bi-layer, transmembrane (mostly)

• Peripheral: do not interact w hydrophobic part of bi-layer, held to surface by non-covalent bonds. Ex: microtubules, microfilaments & intermediate filaments.

Other factors affecting fluidity:

• Saturation: composition of lipid molecules in bi-layer

• Temperature

Bacterial infection in the lungs: typical symptom of cystic fibrosis

How thick is the lipid bilayer: 10nm