UB HIS 401 - Chapter Six Notes (44 pages)

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Biochemistry and Microscopes 10 13 2012 Microscopy 1590 microscope was invented Refined in the 1600s Cell walls first seen by Robert Hooke in 1665 o Looked at dead cells from an oak tree Antoni can Leeuwenhoek o Crafted lenses able to visualize living cells Types of Microscopes o Light Microscope Visible light is passed through the specimen and then through a glass lens The lenses refract bend the light in such a way that the image of a specimen is magnified as it is projected into the eye or a camera Magnify effectively to about 1 000 times the actual size Higher than that details cannot be seen clearly Resolution of 0 2 micrometers to 200 nanometers regardless of magnification Contrast staining to labeling cell components to enhance contrast THREE IMPORTANT PARAMETERS IN MICROSCOPY o Magnification Ratio of an objects image size to its real size o Resolution measure of the clarity of the image The minimum distance two points can be separated and still be distinguished as two points o Contrast Accentuates differences in parts of the samples Electron Microscope EM 1950 o Focuses a beam of electrons through the specimen or onto its surface o Resolution is related to the wave length of the radiation a microscope uses for imaging Electron beams have much shorter wavelengths than visible light Modern electron microscopes have a resolution of 0 002nm Cannot resolve structures smaller than 2nm across Scanning electron microscope SEM o Useful for detailed study of the topography of a specimen o Electron beam scans the surface of them sample Usually coated with a thin film of gold o The beam excited electrons on the surface these secondary electrons are detected by a device that translates the pattern of electrons into an electronic signal to a video screen The result is an image of the specimens surface that appear 3D Transmission Electron Microscope TEM o Used to study internal structure of cells o Transmits electrons through a very thin section of the specimen specimen