The Cell Membrane

Discovery of cells

• The cell theory
  • Development of microscopy
    • Leeuwenhoek constructed simple microscopes
    • Robert Hooke (1665) first report of cells
  • Biogenesis (1840)
    • All living things are composed of cells
    • All cells arise from preexisting cells
  • Working definition: living things are chemical organizations composed of cells and are capable of reproducing themselves

Microscopy

• Three attributes of microscopes make them particularly useful to the cell biologist
  • Magnification: an increase in the apparent size of an object
  • Resolution: the ability to distinguish two adjacent objects
  • Contrast: ability to distinguish one part of a cell from another

Light Microscopy (LM)

• Light is passed through a specimen, bent, captured and refocused by lens
  • Useful magnification limit is 1000x
  • Resolution of human eye is 120mm
    • LM (compound scope) is 0.2mm
  • Contrast is as important as magnification
    • LM requires staining which can be lethal for the cell
    • Nomarski optics use differential light defraction patterns to view living cell

Dissecting Light Microscope

• Use to view the surface of biological tissues
  • View living and non-living tissues
  • Lower power of magnification

Transmission Electron Microscopy (TEM)

• Use an electron beam rather than light to image the object
  • Resolution is 0.0002mm
  • Requires material to be fixed and stained in specific manner
    • View only dead tissues which have been sectioned to ultra-thin slices (600A or 60nm)
    • Typical red blood cell (RBC) is 6000nm
• Scanning Electron Microscopy (SEM)
• Uses electron defraction patterns to view the surfaces of objects
  • resolution is 0.01mm
  • Requires that the biological materials be coated with heavy metal stains
    • Gold plating is the general procedure

Scanning Tunneling Microscope

• Developed from the SEM
  • Uses a very fine electron emitting tip that moves back and forth over a metal coated surface.
  • Recording the constant adjustment in tip height to maintain a constant current, a computer can translate the distances into a surface