AV

2.2 Cell Membrane

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